657d0687e9
The "revised" timestamps were outdated and are not updated as the docs are updated, so better remove them. Update times can be inferred from VCS.
1340 lines
50 KiB
HTML
1340 lines
50 KiB
HTML
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<title>Filesystem Tutorial</title>
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<td width="277">
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<a href="../../../index.htm">
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<img src="../../../boost.png" alt="boost.png (6897 bytes)" align="middle" width="300" height="86" border="0"></a></td>
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<td align="middle">
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<font size="7">Filesystem Tutorial</font>
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</td>
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</tr>
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</table>
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<table border="0" cellpadding="5" cellspacing="0" style="border-collapse: collapse"
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bordercolor="#111111" bgcolor="#D7EEFF" width="100%">
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<tr>
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<td><a href="index.htm">Home</a>
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<a href="tutorial.html">Tutorial</a>
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<a href="reference.html">Reference</a>
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<a href="faq.htm">FAQ</a>
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<a href="release_history.html">Releases</a>
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<a href="portability_guide.htm">Portability</a>
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<a href="v4.html">V4</a>
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<a href="v3.html">V3 Intro</a>
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<a href="v3_design.html">V3 Design</a>
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<a href="deprecated.html">Deprecated</a>
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<a href="issue_reporting.html">Bug Reports </a>
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</td>
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</table>
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<p>
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<a href="#Introduction">Introduction</a><br>
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<a href="#Preliminaries">Preliminaries</a><br>
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<a href="#Reporting-size">Reporting the size of a file - (tut1.cpp)</a><br>
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<a href="#Using-status-queries">Using status queries to determine file existence and type - (tut2.cpp)</a><br>
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<a href="#Directory-iteration">Directory iteration plus catching
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exceptions - (tut3.cpp)</a><br>
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<a href="#Using-path-decomposition">Using path decomposition, plus sorting results - (tut4.cpp)</a><br>
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<a href="#Class-path-Constructors">Class path: Constructors, including
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Unicode - (tut5.cpp)</a><br>
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<a href="#Class-path-formats">Class path: Generic format vs. Native format</a><br>
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<a href="#Class path-iterators-etc">Class path: Iterators, observers, composition, decomposition, and query - (path_info.cpp)</a><br>
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<a href="#Error-reporting">Error reporting</a><br>
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</p>
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<h2><a name="Introduction">Introduction</a></h2>
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<p>This tutorial develops a little command line program to list information
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about files and directories - essentially a much simplified version of the POSIX <code>ls</code> or Windows <code>dir</code>
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commands. We'll start with the simplest possible version and progress to more
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complex functionality. Along the way we'll digress to cover topics you'll need
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to know about to understand Boost.Filesystem.</p>
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<p>Source code for each of the tutorial programs is available, and you
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are encouraged to compile, test, and experiment with it. To conserve space, we won't
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always show boilerplate code here, but the provided source is complete and
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ready to build.</p>
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<h2><a name="Preliminaries">Preliminaries</a></h2>
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<p>Install the Boost distribution if you haven't already done so. See the
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<a href="http://www.boost.org/more/getting_started/index.html">Boost Getting
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Started</a> docs.</p>
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<p>This tutorial assumes you are going to compile and test the examples using
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the provided scripts. That's highly recommended.</p>
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<blockquote>
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<p><b>If you are planning to compile and test the examples but not use the
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scripts, make sure your build setup knows where to
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locate or build the Boost library binaries.</b></p>
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</blockquote>
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<p>Fire up your command line interpreter, and type the following commands:</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Ubuntu Linux </b></i></td>
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</tr>
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<tr>
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<td>
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<pre>$ cd <i><b>boost-root</b></i>/libs/filesystem/example/test
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$ ./setup.sh
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Copying example programs...
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$ ./build.sh
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Compiling example programs...
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$ ./tut1
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Usage: tut1 path</pre>
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</td>
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</tr>
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</table>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Microsoft Windows</b></i></td>
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</tr>
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<tr>
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<td>
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<pre>>cd <i><b>boost-root</b></i>\libs\filesystem\example\test
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>setup
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Copying example programs...
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>build
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Compiling example programs...
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>tut1
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Usage: tut1 path</pre>
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</td>
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</tr>
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</table>
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<p>If the <code>tut1</code> command outputs "<code>Usage: tut1 path</code>", all
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is well. A set of tutorial example programs has been copied (by <code>setup</code>) to
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<i><b><code>boost-root</code></b></i><code>/libs/filesystem/example/test</code>
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and then built. You are encouraged to modify and experiment with them as the
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tutorial progresses. Just invoke the <code>build</code> script again to rebuild,
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or invoke <code>b2</code> directly.</p>
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<p>If something didn't work right, here are some troubleshooting suggestions:</p>
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<ul>
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<li>If the <code>b2</code> program executable isn't being found, check your path environmental variable
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or see
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<a href="http://www.boost.org/more/getting_started/windows.html">Boost
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Getting Started</a>.<br>
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</li>
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<li>Look at <code>b2.log</code> to try to spot an indication of the
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problem.</li>
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</ul>
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<h2><a name="Reporting-size">Reporting the size of a file</a> - (<a href="../example/tut1.cpp">tut1.cpp</a>)</h2>
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<p>Let's get started. Our first example program, <a href="../example/tut1.cpp">tut1.cpp</a>,
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reports the size of a file:</p>
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<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td>
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<pre><!-- include file "../example/tut1.cpp" -->#include <iostream>
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#include <boost/filesystem.hpp>
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using namespace boost::filesystem;
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int main(int argc, char* argv[])
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{
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if (argc < 2)
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{
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std::cout << "Usage: tut1 path\n";
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return 1;
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}
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std::cout << argv[1] << " " << file_size(argv[1]) << '\n';
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return 0;
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}<!-- end include file --></pre>
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</td>
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</tr>
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</table>
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<p>The Boost.Filesystem <code><a href="reference.html#file_size">file_size</a></code>
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function returns a <code>uintmax_t</code>
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containing the size of the file named by the argument. The declaration looks
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like this:</p>
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<blockquote>
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<pre><code>uintmax_t file_size(const path& p);</code> </pre>
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</blockquote>
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<p>For now, all you need to know is that <code>class path</code> has constructors that take
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<code>const char *</code> and other string types. (If you can't wait to
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find out more, skip ahead to the <a href="#Class-path-Constructors">class path</a> section of
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the tutorial.)</p>
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<p>Please take a minute to try out <code>tut1</code> on your system, using a
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file that is known to exist, such as <code>tut1.cpp</code>. Here is what the
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results look like on two different operating systems:</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Ubuntu Linux </b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>$ ./tut1 tut1.cpp
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tut1.cpp 569</pre>
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<pre>$ ls -l tut1.cpp
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-rw-rw-r-- 1 beman beman 569 Jul 26 12:04 tut1.cpp</pre>
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</td>
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</tr>
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</table>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Microsoft Windows</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>>tut1 tut1.cpp
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tut1.cpp 592
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>dir tut1.cpp
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...
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07/26/2015 07:20 AM 592 tut1.cpp
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...</pre>
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</td>
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</tr>
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</table>
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<p>So far, so good. The reported Linux and Windows sizes are different because
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the Linux tests used <code>"\n"</code> line endings, while the Windows tests
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used <code>"\r\n"</code> line endings. The sizes reported may differ
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from the above if changes have been made to <code>tut1.cpp</code>.</p>
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<p>Now try again, but give a path that doesn't exist:</p>
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<table border="1" cellpadding="5" cellspacing="0"
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style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Ubuntu Linux </b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>$ ./tut1 foo
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terminate called after throwing an instance of 'boost::filesystem::filesystem_error'
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what(): boost::filesystem::file_size: No such file or directory: "foo"
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Aborted (core dumped)</pre>
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</td>
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</tr>
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</table>
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<table border="1" cellpadding="5" cellspacing="0"
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style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Microsoft Windows</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>>tut1 foo</pre>
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<p><b><i>An exception is thrown;<br>
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the exact form of the response depends on
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Windows system options.</i></b></td>
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</tr>
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</table>
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<p>What happens?
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There's no file named <code>foo</code> in the current directory, so by default an
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exception is thrown. See <a href="#Error-reporting">Error reporting</a> to learn
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about error reporting via error codes rather than exceptions.</p>
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<p>Try this:</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Ubuntu Linux </b></i></td>
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</tr>
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<tr>
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<td>
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<pre>$ ./tut1 .
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terminate called after throwing an instance of 'boost::filesystem::filesystem_error'
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what(): boost::filesystem::file_size: Operation not permitted: "."
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Aborted (core dumped)</pre>
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</td>
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</tr>
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</table>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Microsoft Windows</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>>tut1 .</pre>
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<p><b><i>An exception is thrown;<br>
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the exact form of the response depends on Windows system options.</i></b></td>
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</tr>
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</table>
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<p>The current directory exists, but <code>file_size()</code> works on regular
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files, not directories, so again an exception is thrown.</p>
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<p>We'll deal with those situations in <code>tut2.cpp</code>.</p>
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<h2><a name="Using-status-queries">Using status queries to determine file existence and type</a> - (<a href="../example/tut2.cpp">tut2.cpp</a>)</h2>
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<p>Boost.Filesystem includes status query functions such as <code>
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<a href="reference.html#exists-path">exists</a></code>,
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<code><a href="reference.html#is_directory-path">is_directory</a></code>, and <code>
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<a href="reference.html#is_regular_file-path">is_regular_file</a></code>. These return
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<code>bool</code>'s, and will return <code>true</code> if the condition
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described by their name is met. Otherwise they return <code>false</code>,
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including when any element
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of the path argument can't be found.</p>
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<p><a href="../example/tut2.cpp">tut2.cpp</a> uses several of the status query functions to cope with non-existent
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files and with different kinds of files:</p>
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<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td>
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<pre><!-- include file "../example/tut2.cpp" -->#include <iostream>
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#include <boost/filesystem.hpp>
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using namespace std;
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using namespace boost::filesystem;
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int main(int argc, char* argv[])
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{
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if (argc < 2)
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{
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cout << "Usage: tut2 path\n";
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return 1;
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}
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path p(argv[1]); // avoid repeated path construction below
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if (exists(p)) // does path p actually exist?
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{
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if (is_regular_file(p)) // is path p a regular file?
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cout << p << " size is " << file_size(p) << '\n';
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else if (is_directory(p)) // is path p a directory?
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cout << p << " is a directory\n";
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else
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cout << p << " exists, but is not a regular file or directory\n";
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}
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else
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cout << p << " does not exist\n";
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return 0;
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}<!-- end include file --></pre>
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</td>
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</tr>
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</table>
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<p>Give it a try:</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Ubuntu Linux </b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>$ ./tut2 tut2.cpp
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"tut2.cpp" size is 997
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$ ./tut2 foo
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"foo" does not exist
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$ ./tut2 .
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"." is a directory</pre>
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</td>
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</tr>
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</table>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Microsoft Windows</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>>tut2 tut2.cpp
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tut2.cpp size is 1039
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>tut2 foo
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"foo" does not exist
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>tut2 .
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"." is a directory</pre>
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</td>
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</tr>
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</table>
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<p>Although tut2 works OK in these tests, the output is less than satisfactory
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for a directory. We'd typically like to see a list of the directory's contents. In <code>tut3.cpp</code>
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we will see how to iterate over directories.</p>
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<p>But first, let's try one more test:</p>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Ubuntu Linux </b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>$ ls /home/jane/foo
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ls: cannot access /home/jane/foo: No such file or directory
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$ ./tut2 /home/jane/foo
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terminate called after throwing an instance of 'boost::
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filesystem::filesystem_error>'
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what(): boost::filesystem::status: Permission denied:
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"/home/jane/foo"
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Aborted</pre>
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</td>
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</tr>
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</table>
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<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
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<tr>
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<td align="center"><i><b>Microsoft Windows</b></i></td>
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</tr>
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<tr>
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<td valign="top">
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<pre>>dir e:\
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The device is not ready.
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>tut2 e:\</pre>
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<p dir="ltr"><b><i>An exception is thrown;<br>
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the exact form of the response depends on
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Windows system options.</i></b></td>
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</tr>
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</table>
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<p>On the Linux system, the test was being run from an account that did not have
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permission to access <code>/home/jane/foo</code>. On the Windows system, <code>
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e:</code> was a Compact Disc reader/writer that was not ready. End users
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shouldn't have to interpret cryptic exceptions reports, so as we move on to <code>tut3.cpp</code>
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we will increase the robustness of the code, too.</p>
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<h2><a name="Directory-iteration">Directory iteration</a> plus catching
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exceptions - (<a href="../example/tut3.cpp">tut3.cpp</a>)</h2>
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<p>Boost.Filesystem's <code><a href="reference.html#directory_iterator">
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directory_iterator</a></code> class is just what we need here. It follows the
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general pattern of the standard library's <code>istream_iterator</code>. Constructed from
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a path, it iterates over the contents of the directory. A default constructed <code>directory_iterator</code>
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acts as the end iterator.</p>
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<p>The value type of <code>directory_iterator</code> is <code>
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<a href="reference.html#directory_entry">directory_entry</a></code>. A <code>
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directory_entry</code> object contains <code>path</code> and <code><a href="reference.html#file_status">file_status</a></code>
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information. A <code>
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directory_entry</code> object
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can be used directly, but can also be passed to <code>path</code> arguments in function calls.</p>
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<p>The other need is increased robustness in the face of the many kinds of
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errors that can affect file system operations. We could do that at the level of
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each call to a Boost.Filesystem function (see <a href="#Error-reporting">Error
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reporting</a>), but for simplicity <a href="../example/tut3.cpp">tut3.cpp</a>
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uses an overall try/catch block.</p>
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|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/tut3.cpp" -->#include <iostream>
|
|
#include <boost/filesystem.hpp>
|
|
using std::cout;
|
|
using namespace boost::filesystem;
|
|
|
|
int main(int argc, char* argv[])
|
|
{
|
|
if (argc < 2)
|
|
{
|
|
cout << "Usage: tut3 path\n";
|
|
return 1;
|
|
}
|
|
|
|
path p (argv[1]);
|
|
|
|
try
|
|
{
|
|
if (exists(p))
|
|
{
|
|
if (is_regular_file(p))
|
|
cout << p << " size is " << file_size(p) << '\n';
|
|
|
|
else if (is_directory(p))
|
|
{
|
|
cout << p << " is a directory containing:\n";
|
|
|
|
for (directory_entry& x : directory_iterator(p))
|
|
cout << " " << x.path() << '\n';
|
|
}
|
|
else
|
|
cout << p << " exists, but is not a regular file or directory\n";
|
|
}
|
|
else
|
|
cout << p << " does not exist\n";
|
|
}
|
|
|
|
catch (const filesystem_error& ex)
|
|
{
|
|
cout << ex.what() << '\n';
|
|
}
|
|
|
|
return 0;
|
|
}<!-- end include file --></pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>Give <code>tut3</code> a try, passing it a path to a directory as a command line argument.
|
|
Here is a run on a checkout of the Boost Git develop branch, followed by a repeat
|
|
of the test cases that caused exceptions on Linux and Windows:</p>
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Ubuntu Linux </b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">
|
|
<pre>$ ./tut3 ~/boost/develop
|
|
"/home/beman/boost/develop" is a directory containing:
|
|
"/home/beman/boost/develop/rst.css"
|
|
"/home/beman/boost/develop/boost"
|
|
"/home/beman/boost/develop/boost.png"
|
|
"/home/beman/boost/develop/libs"
|
|
"/home/beman/boost/develop/doc"
|
|
"/home/beman/boost/develop/project-config.jam.2"
|
|
"/home/beman/boost/develop/.gitmodules"
|
|
"/home/beman/boost/develop/boostcpp.py"
|
|
"/home/beman/boost/develop/.travis.yml"
|
|
"/home/beman/boost/develop/.gitattributes"
|
|
"/home/beman/boost/develop/index.htm"
|
|
"/home/beman/boost/develop/index.html"
|
|
"/home/beman/boost/develop/bjam"
|
|
"/home/beman/boost/develop/project-config.jam.1"
|
|
"/home/beman/boost/develop/LICENSE_1_0.txt"
|
|
"/home/beman/boost/develop/.git"
|
|
"/home/beman/boost/develop/tools"
|
|
"/home/beman/boost/develop/stage"
|
|
"/home/beman/boost/develop/boostcpp.jam"
|
|
"/home/beman/boost/develop/Jamroot"
|
|
"/home/beman/boost/develop/.gitignore"
|
|
"/home/beman/boost/develop/INSTALL"
|
|
"/home/beman/boost/develop/more"
|
|
"/home/beman/boost/develop/bin.v2"
|
|
"/home/beman/boost/develop/project-config.jam"
|
|
"/home/beman/boost/develop/boost-build.jam"
|
|
"/home/beman/boost/develop/bootstrap.bat"
|
|
"/home/beman/boost/develop/bootstrap.sh"
|
|
"/home/beman/boost/develop/status"
|
|
"/home/beman/boost/develop/boost.css"</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Microsoft Windows</b></i></td>
|
|
</tr>
|
|
<tr>
|
|
|
|
<td valign="top">
|
|
<pre>>tut3 \boost\develop
|
|
"\boost\develop" is a directory containing:
|
|
"\boost\develop\.git"
|
|
"\boost\develop\.gitattributes"
|
|
"\boost\develop\.gitignore"
|
|
"\boost\develop\.gitmodules"
|
|
"\boost\develop\.travis.yml"
|
|
"\boost\develop\bin.v2"
|
|
"\boost\develop\boost"
|
|
"\boost\develop\boost-build.jam"
|
|
"\boost\develop\boost.css"
|
|
"\boost\develop\boost.png"
|
|
"\boost\develop\boostcpp.jam"
|
|
"\boost\develop\boostcpp.py"
|
|
"\boost\develop\bootstrap.bat"
|
|
"\boost\develop\bootstrap.sh"
|
|
"\boost\develop\doc"
|
|
"\boost\develop\index.htm"
|
|
"\boost\develop\index.html"
|
|
"\boost\develop\INSTALL"
|
|
"\boost\develop\Jamroot"
|
|
"\boost\develop\libs"
|
|
"\boost\develop\LICENSE_1_0.txt"
|
|
"\boost\develop\more"
|
|
"\boost\develop\project-config.jam"
|
|
"\boost\develop\rst.css"
|
|
"\boost\develop\stage"
|
|
"\boost\develop\status"
|
|
"\boost\develop\tools"</pre>
|
|
<pre>>tut3 e:\
|
|
boost::filesystem::status: The device is not ready: "e:\"</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>Not bad, but we can make further improvements:</p>
|
|
|
|
<ul>
|
|
<li>The listing would be much easier to read if only the filename was
|
|
displayed, rather than the full path.<br>
|
|
</li>
|
|
<li>The Linux listing isn't sorted. That's because the ordering of
|
|
directory iteration is unspecified. Ordering depends on the underlying
|
|
operating system API and file system specifics. So we need to sort the
|
|
results ourselves. </li>
|
|
</ul>
|
|
|
|
<p>The next sections show how those changes play out, so read on!</p>
|
|
|
|
<h2><a name="Using-path-decomposition">Using path decomposition, plus sorting results</a> - (<a href="../example/tut4.cpp">tut4.cpp</a>)</h2>
|
|
|
|
<p>For directories, <a href="../example/tut4.cpp">tut4.cpp</a> builds a <code>
|
|
std::vector</code> of all the entries and then sorts it before writing to <code>
|
|
cout</code>.</p>
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/tut4.cpp" -->#include <iostream>
|
|
#include <vector>
|
|
#include <algorithm>
|
|
#include <boost/filesystem.hpp>
|
|
using std::cout;
|
|
using namespace boost::filesystem;
|
|
|
|
int main(int argc, char* argv[])
|
|
{
|
|
if (argc < 2)
|
|
{
|
|
cout << "Usage: tut4 path\n";
|
|
return 1;
|
|
}
|
|
|
|
path p (argv[1]);
|
|
|
|
try
|
|
{
|
|
if (exists(p))
|
|
{
|
|
if (is_regular_file(p))
|
|
cout << p << " size is " << file_size(p) << '\n';
|
|
|
|
else if (is_directory(p))
|
|
{
|
|
cout << p << " is a directory containing:\n";
|
|
|
|
std::vector<path> v;
|
|
|
|
for (auto&& x : directory_iterator(p))
|
|
v.push_back(x.path());
|
|
|
|
std::sort(v.begin(), v.end());
|
|
|
|
for (auto&& x : v)
|
|
cout << " " << x.filename() << '\n';
|
|
}
|
|
else
|
|
cout << p << " exists, but is not a regular file or directory\n";
|
|
}
|
|
else
|
|
cout << p << " does not exist\n";
|
|
}
|
|
|
|
catch (const filesystem_error& ex)
|
|
{
|
|
cout << ex.what() << '\n';
|
|
}
|
|
|
|
return 0;
|
|
}<!-- end include file --></pre>
|
|
</blockquote>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>The only difference between <code>tut3.cpp</code> and <code>tut4.cpp</code> is
|
|
what happens for directories. We changed:</p>
|
|
<blockquote>
|
|
<pre>for (const directory_entry& x : directory_iterator(p))
|
|
cout << " " << x.path() << '\n';</pre>
|
|
</blockquote>
|
|
<p>to:</p>
|
|
<blockquote>
|
|
<pre>std::vector<path> v;
|
|
|
|
for (auto&& x : directory_iterator(p))
|
|
v.push_back(x.path());
|
|
|
|
std::sort(v.begin(), v.end());
|
|
|
|
for (auto&& x : v)
|
|
cout << " " << x.filename() << '\n';
|
|
</pre>
|
|
</blockquote>
|
|
<p> <code>
|
|
<a href="reference.html#path-filename">filename()</a></code> is one of
|
|
several class <code>path</code> decomposition functions. It extracts the
|
|
filename portion
|
|
from a path (<font face="Courier New">i.e. </font><code>"index.html"</code><font face="Courier New">
|
|
from </font><code>"/home/beman/boost/trunk/index.html"</code>). These decomposition functions are
|
|
more fully explored in the <a href="#Class path-iterators-etc">Path iterators, observers,
|
|
composition, decomposition and query</a> portion of this tutorial.</p>
|
|
<p>The above was written as two lines of code for clarity. It could have
|
|
been written more concisely as:</p>
|
|
<blockquote>
|
|
<pre>v.push_back(it->path().filename()); // we only care about the filename</pre>
|
|
</blockquote>
|
|
<p>Here is the output from a test of <code><a href="../example/tut4.cpp">tut4.cpp</a></code>:</p>
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Ubuntu Linux </b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<pre>$ ./tut4 v</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Microsoft Windows</b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<pre>$ ./tut4 ~/boost/develop
|
|
"/home/beman/boost/develop" is a directory containing:
|
|
.git
|
|
.gitattributes
|
|
.gitignore
|
|
.gitmodules
|
|
.travis.yml
|
|
INSTALL
|
|
Jamroot
|
|
LICENSE_1_0.txt
|
|
bin.v2
|
|
boost
|
|
boost-build.jam
|
|
boost.css
|
|
boost.png
|
|
boostcpp.jam
|
|
boostcpp.py
|
|
bootstrap.bat
|
|
bootstrap.sh
|
|
doc
|
|
index.htm
|
|
index.html
|
|
libs
|
|
more
|
|
project-config.jam
|
|
project-config.jam.1
|
|
project-config.jam.2
|
|
rst.css
|
|
stage
|
|
status
|
|
tools</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>That completes the main portion of this tutorial. If you haven't already
|
|
worked through the <a href="#Class-path-Constructors">Class path</a> sections of this tutorial, dig into them now.
|
|
The <a href="#Error-reporting">Error reporting</a> section may also be of
|
|
interest, although it can be skipped unless you are deeply concerned about
|
|
error handling issues.</p>
|
|
|
|
<h2><a name="Class-path-Constructors">Class path: Constructors</a>,
|
|
including Unicode - (<a href="../example/tut5.cpp">tut5.cpp</a>)</h2>
|
|
|
|
<p>Traditional C interfaces pass paths as <code>const char*</code> arguments.
|
|
C++ interfaces may add <code>const std::string&</code> overloads, but adding
|
|
overloads becomes untenable if wide characters, containers, and iterator ranges
|
|
need to be supported.</p>
|
|
<p>Passing paths as <code>const path&</code> arguments is far simpler, yet far
|
|
more flexible because class <code>path</code> itself is far more flexible:</p>
|
|
<ol>
|
|
<li>Class <code>path</code> supports multiple character types and encodings, including Unicode, to
|
|
ease internationalization.</li>
|
|
<li>Class <code>path</code> supports multiple source types, such as iterators for null terminated
|
|
sequences, iterator ranges, containers (including <code>std::basic_string</code>),
|
|
and <code><a href="reference.html#Class-directory_entry">directory_entry</a></code>'s,
|
|
so functions taking paths don't need to provide several overloads.</li>
|
|
<li>Class <code>path</code> supports both native and generic pathname formats, so programs can be
|
|
portable between operating systems yet use native formats where desirable.</li>
|
|
<li>Class <code>path</code> supplies a full set of iterators, observers, composition,
|
|
decomposition, and query functions, making pathname manipulations easy,
|
|
convenient, reliable, and portable.</li>
|
|
</ol>
|
|
<p>Here is how (1) and (2) work. Class path constructors,
|
|
assignments, and appends have member templates for sources. For example, here
|
|
are the constructors that take sources:</p>
|
|
|
|
<blockquote>
|
|
<pre>template <class <a href="reference.html#Source">Source</a>>
|
|
path(Source const& source);</pre>
|
|
<pre>template <class InputIterator>
|
|
path(InputIterator begin, InputIterator end);</pre>
|
|
</blockquote>
|
|
<p>Let's look at a little program that shows how comfortable class <code>path</code> is with
|
|
both narrow and wide characters in C-style strings, C++ strings, and via C++
|
|
iterators:</p>
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/tut5.cpp" -->#include <boost/filesystem/fstream.hpp>
|
|
#include <string>
|
|
#include <list>
|
|
namespace fs = boost::filesystem;
|
|
|
|
int main()
|
|
{
|
|
// \u263A is "Unicode WHITE SMILING FACE = have a nice day!"
|
|
std::string narrow_string ("smile2");
|
|
std::wstring wide_string (L"smile2\u263A");
|
|
std::list<char> narrow_list;
|
|
narrow_list.push_back('s');
|
|
narrow_list.push_back('m');
|
|
narrow_list.push_back('i');
|
|
narrow_list.push_back('l');
|
|
narrow_list.push_back('e');
|
|
narrow_list.push_back('3');
|
|
std::list<wchar_t> wide_list;
|
|
wide_list.push_back(L's');
|
|
wide_list.push_back(L'm');
|
|
wide_list.push_back(L'i');
|
|
wide_list.push_back(L'l');
|
|
wide_list.push_back(L'e');
|
|
wide_list.push_back(L'3');
|
|
wide_list.push_back(L'\u263A');
|
|
|
|
{ fs::ofstream f("smile"); }
|
|
{ fs::ofstream f(L"smile\u263A"); }
|
|
{ fs::ofstream f(narrow_string); }
|
|
{ fs::ofstream f(wide_string); }
|
|
{ fs::ofstream f(narrow_list); }
|
|
{ fs::ofstream f(wide_list); }
|
|
narrow_list.pop_back();
|
|
narrow_list.push_back('4');
|
|
wide_list.pop_back();
|
|
wide_list.pop_back();
|
|
wide_list.push_back(L'4');
|
|
wide_list.push_back(L'\u263A');
|
|
{ fs::ofstream f(fs::path(narrow_list.begin(), narrow_list.end())); }
|
|
{ fs::ofstream f(fs::path(wide_list.begin(), wide_list.end())); }
|
|
|
|
return 0;
|
|
}<!-- end include file --></pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>Testing <code>tut5</code>:</p>
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Ubuntu Linux </b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">
|
|
<pre>$ ./tut5
|
|
|
|
$ ls smile*
|
|
smile smile☺ smile2 smile2☺ smile3 smile3☺ smile4 smile4☺</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Microsoft Windows</b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td valign="top">
|
|
<pre>>tut5
|
|
|
|
>dir /b smile*
|
|
smile
|
|
smile2
|
|
smile2☺
|
|
smile3
|
|
smile3☺
|
|
smile4
|
|
smile4☺
|
|
smile☺</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>The exact appearance of the smiling face will depend on the font,
|
|
font size, and other settings for your command line window. The above tests were
|
|
run with out-of-the-box Ubuntu 14.04 and Windows 7, US Edition. If you don't get
|
|
the above results, take a look at the <code><i>boost-root</i>/libs/filesystem/example/test</code>
|
|
directory with your system's GUI file browser, such as Linux Nautilus, Mac OS X
|
|
Finder, or Windows Explorer. These tend to be more comfortable with
|
|
international character sets than command line interpreters.</p>
|
|
|
|
<p>Class <code>path</code> takes care of whatever character type or encoding
|
|
conversions are required by the particular operating system. Thus as <code>
|
|
tut5</code> demonstrates, it's no problem to pass a wide character string to a
|
|
Boost.Filesystem operational function even if the underlying operating system
|
|
uses narrow characters, and visa versa. And the same applies to user supplied
|
|
functions that take <code>const path&</code> arguments.</p>
|
|
|
|
<p>Class <code>path</code> also provides path syntax that is portable across operating systems,
|
|
element iterators, and observer, composition, decomposition, and query
|
|
functions to manipulate the elements of a path. The next section of this
|
|
tutorial deals with path syntax.</p>
|
|
|
|
<h2><a name="Class-path-formats">Class path: Generic format vs. Native format</a></h2>
|
|
|
|
<p>Class <code>path</code> deals with two different pathname
|
|
formats - generic format and native format. For POSIX-like
|
|
file systems, these formats are the same. But for users of Windows and
|
|
other non-POSIX file systems, the distinction is important. Even
|
|
programmers writing for POSIX-like systems need to understand the distinction if
|
|
they want their code to be portable to non-POSIX systems.</p>
|
|
|
|
<p>The <b>generic format</b> is the familiar <code>/my_directory/my_file.txt</code> format used by POSIX-like
|
|
operating systems such as the Unix variants, Linux, and Mac OS X. Windows also
|
|
recognizes the generic format, and it is the basis for the familiar Internet URL
|
|
format. The directory
|
|
separator character is always one or more slash characters.</p>
|
|
|
|
<p>The <b>native format</b> is the format as defined by the particular
|
|
operating system. For Windows, either the slash or the backslash can be used as
|
|
the directory separator character, so <code>/my_directory\my_file.txt</code>
|
|
would work fine. Of course, if you write that in a C++ string literal, it
|
|
becomes <code>"/my_directory\\my_file.txt"</code>.</p>
|
|
|
|
<p>If a drive specifier or a backslash appears
|
|
in a pathname on a Windows system, it is always treated as the native format.</p>
|
|
|
|
<p>Class <code>path</code> has observer functions that allow you to
|
|
obtain the string representation of a path object in either the native format
|
|
or the generic format. See the <a href="#Class path-iterators-etc">next section</a>
|
|
for how that plays out.</p>
|
|
|
|
<p>The distinction between generic format and native format is important when
|
|
communicating with native C-style API's and with users. Both tend to expect
|
|
paths in the native format and may be confused by the generic format. The generic
|
|
format is great, however, for writing portable programs that work regardless
|
|
of operating system.</p>
|
|
|
|
<p>The next section covers class <code>path</code> observers, composition,
|
|
decomposition, query, and iteration over the elements of a path.</p>
|
|
|
|
<h2><a name="Class path-iterators-etc">Class path: Iterators, observers, composition, decomposition, and query</a>
|
|
- (<a href="../example/path_info.cpp">path_info.cpp</a>)</h2>
|
|
|
|
<p>The <code><a href="../example/path_info.cpp">path_info.cpp</a></code> program is handy for learning how class <code>path</code>
|
|
iterators,
|
|
observers, composition, decomposition, and query functions work on your system.
|
|
It is one of the programs built by the <code>build.sh</code> and <code>build.bat</code>
|
|
scripts:</p>
|
|
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/path_info.cpp" -->#include <iostream>
|
|
#include <boost/filesystem.hpp>
|
|
using namespace std;
|
|
using namespace boost::filesystem;
|
|
|
|
const char * say_what(bool b) { return b ? "true" : "false"; }
|
|
|
|
int main(int argc, char* argv[])
|
|
{
|
|
if (argc < 2)
|
|
{
|
|
cout << "Usage: path_info path-element [path-element...]\n"
|
|
"Composes a path via operator/= from one or more path-element arguments\n"
|
|
"Example: path_info foo/bar baz\n"
|
|
# ifdef BOOST_POSIX_API
|
|
" would report info about the composed path foo/bar/baz\n";
|
|
# else // BOOST_WINDOWS_API
|
|
" would report info about the composed path foo/bar\\baz\n";
|
|
# endif
|
|
return 1;
|
|
}
|
|
|
|
path p;
|
|
for (; argc > 1; --argc, ++argv)
|
|
p /= argv[1]; // compose path p from the command line arguments
|
|
|
|
cout << "\ncomposed path:\n";
|
|
cout << " operator<<()---------: " << p << "\n";
|
|
cout << " make_preferred()-----: " << p.make_preferred() << "\n";
|
|
|
|
cout << "\nelements:\n";
|
|
for (auto element : p)
|
|
cout << " " << element << '\n';
|
|
|
|
cout << "\nobservers, native format:" << endl;
|
|
# ifdef BOOST_POSIX_API
|
|
cout << " native()-------------: " << p.native() << endl;
|
|
cout << " c_str()--------------: " << p.c_str() << endl;
|
|
# else // BOOST_WINDOWS_API
|
|
wcout << L" native()-------------: " << p.native() << endl;
|
|
wcout << L" c_str()--------------: " << p.c_str() << endl;
|
|
# endif
|
|
cout << " string()-------------: " << p.string() << endl;
|
|
wcout << L" wstring()------------: " << p.wstring() << endl;
|
|
|
|
cout << "\nobservers, generic format:\n";
|
|
cout << " generic_string()-----: " << p.generic_string() << endl;
|
|
wcout << L" generic_wstring()----: " << p.generic_wstring() << endl;
|
|
|
|
cout << "\ndecomposition:\n";
|
|
cout << " root_name()----------: " << p.root_name() << '\n';
|
|
cout << " root_directory()-----: " << p.root_directory() << '\n';
|
|
cout << " root_path()----------: " << p.root_path() << '\n';
|
|
cout << " relative_path()------: " << p.relative_path() << '\n';
|
|
cout << " parent_path()--------: " << p.parent_path() << '\n';
|
|
cout << " filename()-----------: " << p.filename() << '\n';
|
|
cout << " stem()---------------: " << p.stem() << '\n';
|
|
cout << " extension()----------: " << p.extension() << '\n';
|
|
|
|
cout << "\nquery:\n";
|
|
cout << " empty()--------------: " << say_what(p.empty()) << '\n';
|
|
cout << " is_absolute()--------: " << say_what(p.is_absolute()) << '\n';
|
|
cout << " has_root_name()------: " << say_what(p.has_root_name()) << '\n';
|
|
cout << " has_root_directory()-: " << say_what(p.has_root_directory()) << '\n';
|
|
cout << " has_root_path()------: " << say_what(p.has_root_path()) << '\n';
|
|
cout << " has_relative_path()--: " << say_what(p.has_relative_path()) << '\n';
|
|
cout << " has_parent_path()----: " << say_what(p.has_parent_path()) << '\n';
|
|
cout << " has_filename()-------: " << say_what(p.has_filename()) << '\n';
|
|
cout << " has_stem()-----------: " << say_what(p.has_stem()) << '\n';
|
|
cout << " has_extension()------: " << say_what(p.has_extension()) << '\n';
|
|
|
|
return 0;
|
|
}<!-- end include file --></pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
<p>Run the examples below on your system, and try some different path arguments
|
|
as we go along. Here is the invocation we will talk about in detail:</p>
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Ubuntu Linux </b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<pre>$ ./path_info /foo bar baa.txt
|
|
|
|
composed path:
|
|
operator<<()---------: "/foo/bar/baa.txt"
|
|
make_preferred()-----: "/foo/bar/baa.txt"
|
|
|
|
elements:
|
|
"/"
|
|
"foo"
|
|
"bar"
|
|
"baa.txt"
|
|
|
|
observers, native format:
|
|
native()-------------: /foo/bar/baa.txt
|
|
c_str()--------------: /foo/bar/baa.txt
|
|
string()-------------: /foo/bar/baa.txt
|
|
wstring()------------: /foo/bar/baa.txt
|
|
|
|
observers, generic format:
|
|
generic_string()-----: /foo/bar/baa.txt
|
|
generic_wstring()----: /foo/bar/baa.txt
|
|
|
|
decomposition:
|
|
root_name()----------: ""
|
|
root_directory()-----: "/"
|
|
root_path()----------: "/"
|
|
relative_path()------: "foo/bar/baa.txt"
|
|
parent_path()--------: "/foo/bar"
|
|
filename()-----------: "baa.txt"
|
|
stem()---------------: "baa"
|
|
extension()----------: ".txt"
|
|
|
|
query:
|
|
empty()--------------: false
|
|
is_absolute()--------: true
|
|
has_root_name()------: false
|
|
has_root_directory()-: true
|
|
has_root_path()------: true
|
|
has_relative_path()--: true
|
|
has_parent_path()----: true
|
|
has_filename()-------: true
|
|
has_stem()-----------: true
|
|
has_extension()------: true</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
|
|
<table border="1" cellpadding="5" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td align="center"><i><b>Microsoft Windows</b></i></td>
|
|
</tr>
|
|
<tr>
|
|
<td>
|
|
<pre>>path_info \foo bar baa.txt
|
|
|
|
composed path:
|
|
operator<<()---------: "\foo\bar\baa.txt"
|
|
make_preferred()-----: "\foo\bar\baa.txt"
|
|
|
|
elements:
|
|
"/"
|
|
"foo"
|
|
"bar"
|
|
"baa.txt"
|
|
|
|
observers, native format:
|
|
native()-------------: \foo\bar\baa.txt
|
|
c_str()--------------: \foo\bar\baa.txt
|
|
string()-------------: \foo\bar\baa.txt
|
|
wstring()------------: \foo\bar\baa.txt
|
|
|
|
observers, generic format:
|
|
generic_string()-----: /foo/bar/baa.txt
|
|
generic_wstring()----: /foo/bar/baa.txt
|
|
|
|
decomposition:
|
|
root_name()----------: ""
|
|
root_directory()-----: "\"
|
|
root_path()----------: "\"
|
|
relative_path()------: "foo\bar\baa.txt"
|
|
parent_path()--------: "\foo\bar"
|
|
filename()-----------: "baa.txt"
|
|
stem()---------------: "baa"
|
|
extension()----------: ".txt"
|
|
|
|
query:
|
|
empty()--------------: false
|
|
is_absolute()--------: false
|
|
has_root_name()------: false
|
|
has_root_directory()-: true
|
|
has_root_path()------: true
|
|
has_relative_path()--: true
|
|
has_parent_path()----: true
|
|
has_filename()-------: true
|
|
has_stem()-----------: true
|
|
has_extension()------: true</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>We will go through the above code in detail to gain a better
|
|
understanding of what is going on.</p>
|
|
|
|
<p dir="ltr">A common need is to compose a path from its constituent
|
|
directories. Class <code>path</code> uses <code>/</code> and <code>/=</code> operators to
|
|
append elements. That's a reminder
|
|
that these operations append the operating system's preferred directory
|
|
separator if needed. The preferred
|
|
directory separator is a slash on POSIX-like systems, and a backslash on
|
|
Windows-like systems.</p>
|
|
|
|
<p dir="ltr">That's what this code does before displaying the resulting <code>
|
|
path p</code> using the <code>class path</code> stream inserter: </p>
|
|
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/path_info.cpp" --> path p;
|
|
for (; argc > 1; --argc, ++argv)
|
|
p /= argv[1]; // compose path p from the command line arguments
|
|
|
|
cout << "\ncomposed path:\n";
|
|
cout << " operator<<()---------: " << p << "\n";
|
|
cout << " make_preferred()-----: " << p.make_preferred() << "\n";</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
<p>One abstraction for thinking about a path is as a sequence of elements, where
|
|
the elements are directory and file names. To support this abstraction, class
|
|
<code>path</code> provides STL-like iterators and also <code>begin()</code>
|
|
and <code>end()</code> functions.</p>
|
|
|
|
<p>Here is the code that produced the list of elements in the above output listing:</p>
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre>cout << "\nelements:\n";
|
|
for (auto element : p)
|
|
cout << " " << element << '\n';</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
<p>Let's look at class path observer functions:</p>
|
|
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/path_info.cpp" --> cout << "\nobservers, native format:" << endl;
|
|
# ifdef BOOST_POSIX_API
|
|
cout << " native()-------------: " << p.native() << endl;
|
|
cout << " c_str()--------------: " << p.c_str() << endl;
|
|
# else // BOOST_WINDOWS_API
|
|
wcout << L" native()-------------: " << p.native() << endl;
|
|
wcout << L" c_str()--------------: " << p.c_str() << endl;
|
|
# endif
|
|
cout << " string()-------------: " << p.string() << endl;
|
|
wcout << L" wstring()------------: " << p.wstring() << endl;
|
|
|
|
cout << "\nobservers, generic format:\n";
|
|
cout << " generic_string()-----: " << p.generic_string() << endl;
|
|
wcout << L" generic_wstring()----: " << p.generic_wstring() << endl;</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
<p>Native format observers should be used when interacting with the
|
|
operating system or with users; that's what they expect.</p>
|
|
|
|
<p>Generic format observers should be used when the results need to be
|
|
portable and uniform regardless of the operating system.</p>
|
|
|
|
<p><code>path</code> objects always hold pathnames in the native
|
|
format, but otherwise leave them unchanged from their source. The
|
|
<a href="reference.html#preferred">preferred()</a> function will convert to the
|
|
preferred form, if the native format has several forms. Thus on Windows, it will
|
|
convert slashes to backslashes.</p>
|
|
|
|
<p>Moving on to decomposition:</p>
|
|
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/path_info.cpp" --> cout << "\ndecomposition:\n";
|
|
cout << " root_name()----------: " << p.root_name() << '\n';
|
|
cout << " root_directory()-----: " << p.root_directory() << '\n';
|
|
cout << " root_path()----------: " << p.root_path() << '\n';
|
|
cout << " relative_path()------: " << p.relative_path() << '\n';
|
|
cout << " parent_path()--------: " << p.parent_path() << '\n';
|
|
cout << " filename()-----------: " << p.filename() << '\n';
|
|
cout << " stem()---------------: " << p.stem() << '\n';
|
|
cout << " extension()----------: " << p.extension() << '\n';</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
<p> And, finally, query functions:</p>
|
|
|
|
|
|
<table border="1" cellpadding="3" cellspacing="0" style="border-collapse: collapse" bordercolor="#111111" bgcolor="#D7EEFF">
|
|
<tr>
|
|
<td>
|
|
<pre><!-- include file "../example/path_info.cpp" --> cout << "\nquery:\n";
|
|
cout << " empty()--------------: " << say_what(p.empty()) << '\n';
|
|
cout << " is_absolute()--------: " << say_what(p.is_absolute()) << '\n';
|
|
cout << " has_root_name()------: " << say_what(p.has_root_name()) << '\n';
|
|
cout << " has_root_directory()-: " << say_what(p.has_root_directory()) << '\n';
|
|
cout << " has_root_path()------: " << say_what(p.has_root_path()) << '\n';
|
|
cout << " has_relative_path()--: " << say_what(p.has_relative_path()) << '\n';
|
|
cout << " has_parent_path()----: " << say_what(p.has_parent_path()) << '\n';
|
|
cout << " has_filename()-------: " << say_what(p.has_filename()) << '\n';
|
|
cout << " has_stem()-----------: " << say_what(p.has_stem()) << '\n';
|
|
cout << " has_extension()------: " << say_what(p.has_extension()) << '\n';</pre>
|
|
</td>
|
|
</tr>
|
|
</table>
|
|
|
|
|
|
<p>These are pretty self-evident, but do note the difference in the
|
|
result of <code>is_absolute()</code> between Linux and Windows. Because there is
|
|
no root name (i.e. drive specifier or network name), a lone slash (or backslash)
|
|
is a relative path on Windows but an absolute path on POSIX-like operating
|
|
systems. </p>
|
|
|
|
<h2><a name="Error-reporting">Error reporting</a></h2>
|
|
|
|
<p>The Boost.Filesystem <code>file_size</code> function, like many of the
|
|
operational functions, has two overloads:</p>
|
|
|
|
<blockquote>
|
|
<pre>uintmax_t <a name="file_size">file_size</a>(const path& p);
|
|
uintmax_t <a name="file_size2">file_size</a>(const path& p, system::error_code& ec);</pre>
|
|
</blockquote>
|
|
<p>The only significant difference between the two is how they report errors.</p>
|
|
<p>The
|
|
first signature will throw exceptions to report errors. A <code>
|
|
<a href="reference.html#Class-filesystem_error">filesystem_error</a></code> exception will be thrown
|
|
on an
|
|
operational error. <code>filesystem_error</code> is derived from <code>std::runtime_error</code>.
|
|
It has a
|
|
member function to obtain the <code>
|
|
<a href="../../system/doc/reference.html#Class-error_code">error_code</a></code> reported by the source
|
|
of the error. It also has member functions to obtain the path or paths that caused
|
|
the error.</p>
|
|
|
|
<blockquote>
|
|
|
|
<p><b>Motivation for the second signature:</b> Throwing exceptions on errors was the entire error reporting story for the earliest versions of
|
|
Boost.Filesystem, and indeed throwing exceptions on errors works very well for
|
|
many applications. But user reports trickled in that some code became so
|
|
littered with try and catch blocks as to be unreadable and unmaintainable. In
|
|
some applications I/O errors aren't exceptional, and that's the use case for
|
|
the second signature.</p>
|
|
|
|
</blockquote>
|
|
|
|
<p>Functions with a <code>system::error_code&</code> argument set that
|
|
argument to report operational error status, and so do not throw exceptions when I/O
|
|
related errors occur. For a full explanation, see
|
|
<a href="reference.html#Error-reporting">Error reporting</a> in the reference
|
|
documentation. </p>
|
|
|
|
<hr>
|
|
<p>© Copyright Beman Dawes 2010, 2015</p>
|
|
<p>Distributed under the Boost Software License, Version 1.0. See
|
|
<a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/LICENSE_1_0.txt</a></p>
|
|
|
|
</body>
|
|
|
|
</html>
|