1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
|
[/
Copyright 2006-2007 John Maddock.
Distributed under 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).
]
[section:boost_format_syntax Boost-Extended Format String Syntax]
Boost-Extended format strings treat all characters as literals except for
'$', '\\', '(', ')', '?', and ':'.
[h4 Grouping]
The characters '(' and ')' perform lexical grouping, so use \\( and \\) if you
want a to output literal parenthesis.
[h4 Conditionals]
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.
For example, the format string "(?1foo:bar)" will replace each match found with "foo" if
the sub-expression $1 was matched, and with "bar" otherwise.
[h4 Placeholder Sequences]
Placeholder sequences specify that some part of what matched the regular expression
should be sent to output as follows:
[table
[[Placeholder][Meaning]]
[[$&][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.
[h4 Escape Sequences]
An escape character followed by any character x, outputs that character unless
x is one of the escape sequences shown below.
[table
[[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.]]
]
[endsect]
|
