103 lines
3.6 KiB
Plaintext
103 lines
3.6 KiB
Plaintext
[/
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Copyright 2006-2007 John Maddock.
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at
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http://www.boost.org/LICENSE_1_0.txt).
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]
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[section:boost_format_syntax Boost-Extended Format String Syntax]
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Boost-Extended format strings treat all characters as literals except for
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'$', '\\', '(', ')', '?', and ':'.
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[h4 Grouping]
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The characters '(' and ')' perform lexical grouping, so use \\( and \\) if you
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want a to output literal parenthesis.
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[h4 Conditionals]
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The character '?' begins a conditional expression, the general form is:
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?Ntrue-expression:false-expression
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where N is decimal digit.
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If sub-expression N was matched, then true-expression is evaluated and sent to
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output, otherwise false-expression is evaluated and sent to output.
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You will normally need to surround a conditional-expression with parenthesis in
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order to prevent ambiguities.
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For example, the format string "(?1foo:bar)" will replace each match found with "foo" if
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the sub-expression $1 was matched, and with "bar" otherwise.
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For sub-expressions with an index greater than 9, or for access to named sub-expressions use:
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?{INDEX}true-expression:false-expression
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or
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?{NAME}true-expression:false-expression
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[h4 Placeholder Sequences]
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Placeholder sequences specify that some part of what matched the regular expression
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should be sent to output as follows:
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[table
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[[Placeholder][Meaning]]
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[[$&][Outputs what matched the whole expression.]]
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[[$MATCH][As $&]]
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[[${^MATCH}][As $&]]
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[[$\`][Outputs the text between the end of the last match found (or the
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start of the text if no previous match was found), and the start
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of the current match.]]
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[[$PREMATCH][As $\`]]
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[[${^PREMATCH}][As $\`]]
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[[$'][Outputs all the text following the end of the current match.]]
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[[$POSTMATCH][As $']]
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[[${^POSTMATCH}][As $']]
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[[$+][Outputs what matched the last marked sub-expression in the regular expression.]]
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[[$LAST_PAREN_MATCH][As $+]]
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[[$LAST_SUBMATCH_RESULT][Outputs what matched the last sub-expression to be actually matched.]]
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[[$^N][As $LAST_SUBMATCH_RESULT]]
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[[$$][Outputs a literal '$']]
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[[$n][Outputs what matched the n'th sub-expression.]]
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[[${n}][Outputs what matched the n'th sub-expression.]]
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[[$+{NAME}][Outputs whatever matched the sub-expression named "NAME".]]
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]
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Any $-placeholder sequence not listed above, results in '$' being treated as a literal.
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[h4 Escape Sequences]
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An escape character followed by any character x, outputs that character unless
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x is one of the escape sequences shown below.
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[table
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[[Escape][Meaning]]
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[[\\a][Outputs the bell character: '\\a'.]]
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[[\\e][Outputs the ANSI escape character (code point 27).]]
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[[\\f][Outputs a form feed character: '\\f']]
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[[\\n][Outputs a newline character: '\\n'.]]
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[[\\r][Outputs a carriage return character: '\\r'.]]
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[[\\t][Outputs a tab character: '\\t'.]]
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[[\\v][Outputs a vertical tab character: '\\v'.]]
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[[\\xDD][Outputs the character whose hexadecimal code point is 0xDD]]
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[[\\x{DDDD}][Outputs the character whose hexadecimal code point is 0xDDDDD]]
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[[\\cX][Outputs the ANSI escape sequence "escape-X".]]
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[[\\D][If D is a decimal digit in the range 1-9, then outputs the text that matched sub-expression D.]]
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[[\\l][Causes the next character to be outputted, to be output in lower case.]]
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[[\\u][Causes the next character to be outputted, to be output in upper case.]]
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[[\\L][Causes all subsequent characters to be output in lower case, until a \\E is found.]]
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[[\\U][Causes all subsequent characters to be output in upper case, until a \\E is found.]]
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[[\\E][Terminates a \\L or \\U sequence.]]
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]
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[endsect]
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