|
|
Boost.RegexBoost-Extended Format String Syntax |
|
Boost-Extended format strings treat all characters as literals except for '$', '\', '(', ')', '?', ':' and '\'.
The characters '(' and ')' perform lexical grouping, use \( and \) if you want a to output literal parenthesis.
The character '?' begins a conditional expression, the general form is:
?Ntrue-expression:false-expression
where N is decimal digit.
If sub-expression N was matched, then true-expression is evaluated and sent to output, otherwise false-expression is evaluated and sent to output.
You will normally need to surround a conditional-expression with parenthesis in order to prevent ambiguities.
Placeholder sequences specify that some part of what matched the regular expression should be sent to output as follows:
| Placeholder | Meaning |
| $& | Outputs what matched the whole expression. |
| $` | Outputs the text between the end of the last match found (or the start of the text if no previous match was found), and the start of the current match. |
| $' | Outputs all the text following the end of the current match. |
| $$ | Outputs a literal '$' |
| $n | Outputs what matched the n'th sub-expression. |
Any $-placeholder sequence not listed above, results in '$' being treated as a literal.
An escape character followed by any character x, outputs that character unless x is one of the escape sequences shown below.
| Escape | Meaning |
| \a | Outputs the bell character: '\a'. |
| \e | Outputs the ANSI escape character (code point 27). |
| \f | Outputs a form feed character: '\f' |
| \n | Outputs a newline character: '\n'. |
| \r | Outputs a carriage return character: '\r'. |
| \t | Outputs a tab character: '\t'. |
| \v | Outputs a vertical tab character: '\v'. |
| \xDD | Outputs the character whose hexadecimal code point is 0xDD |
| \x{DDDD} | Outputs the character whose hexadecimal code point is 0xDDDDD |
| \cX | Outputs the ANSI escape sequence "escape-X". |
| \D | If D is a decimal digit in the range 1-9, then outputs the text that matched sub-expression D. |
| \l | Causes the next character to be outputted, to be output in lower case. |
| \u | Causes the next character to be outputted, to be output in upper case. |
| \L | Causes all subsequent characters to be output in lower case, until a \E is found. |
| \U | Causes all subsequent characters to be output in upper case, until a \E is found. |
| \E | Terminates a \L or \U sequence. |
Revised 24 Nov 2004
© Copyright John Maddock 2004
Use, modification and distribution are subject to the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
