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在c++中，有三种正则可以选择使用，C ++regex，C regex，boost regex ，如果在windows下开发c++，默认不支持后面两种正则，如果想快速应用，显然C++ regex 比较方便使用。文章将讨论C++ regex 正则表达式的使用。
C++ regex函数有3个：regex_match、 regex_search 、regex_replace
regex_match
regex_match是正则表达式匹配的函数，下面以例子说明。如果想系统的了解，参考
[cpp]
| 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 | #include <iostream> #include <regex> #include <string> int main( void ){ if (std::regex_match( "subject" ,std::regex( "(sub).(.*)" ))){ std::cout << "string literal matched\n" ; } std::string s( "subject" ); std::regex e( "(sub)(.*)" ); if (std::regex_match(s,e)){ std::cout << "string literal matched\n" ; } std::cmatch cm; std::regex_match( "subject" ,cm,e); std::cout << "string literal with" << cm.size() << "matches\n" ; std::smatch sm; std::regex_match(s,sm,e); std::cout << "string object with" << sm.size() << " matcheds\n" ; std::regex_match(s.cbegin(),s.cend(),sm,e); std::cout << "range with" << sm.size() << " matched\n" ; std::regex_match( "subject" ,cm,e,std::regex_constants::match_default); std::cout << "the matches were:" ; for (unsigned i = 0;i<sm.size();++i){ std::cout << "[" << sm.str() << "]" ; } std::cout << '\n' ; for (unsigned i = 0;i<sm.size();++i){ std::cout << "[" << sm[i] << "]" ; } } |
输出如下：
[plain]
string literal matched
string literal with3matches
string object with3 matcheds
range with3 matched
the matches were:[subject][subject][subject]
[subject][sub][ject]
regex_search
regex_match是另外一个正则表达式匹配的函数，下面是regex_search的例子。regex_search和regex_match的主要区别是：regex_match是全词匹配，而regex_search是搜索其中匹配的字符串。如果想系统了解，请参考
[cpp]
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | // regex_search example #include <iostream> #include <regex> #include <string> int main(){ std::string s ( "this subject has a submarine as a subsequence" ); std::smatch m; std::regex e ( "\\b(sub)([^ ]*)" ); // matches words beginning by "sub" std::cout << "Target sequence: " << s << std::endl; std::cout << "Regular expression: /\\b(sub)([^ ]*)/" << std::endl; std::cout << "The following matches and submatches were found:" << std::endl; while (std::regex_search (s,m,e)) { for ( auto x=m.begin();x!=m.end();x++) std::cout << x->str() << " " ; std::cout << "--> ([^ ]*) match " << m.format( "$2" ) <<std::endl; s = m.suffix().str(); } } |
输出如下：
[plain]
Target sequence: this subject has a submarine as a subsequence
Regular expression: /\b(sub)([^ ]*)/
The following matches and submatches were found:
subject sub ject --> ([^ ]*) match ject
submarine sub marine --> ([^ ]*) match marine
subsequence sub sequence --> ([^ ]*) match sequence
[cpp]
regex_replace
regex_replace是替换正则表达式匹配内容的函数，下面是regex_replace的例子。如果想系统了解，请参考
[cpp]
| 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 | #include <regex> #include <iostream> int main() { char buf[20]; const char *first = "axayaz" ; const char *last = first + strlen (first); std::regex rx( "a" ); std::string fmt( "A" ); std::regex_constants::match_flag_type fonly = std::regex_constants::format_first_only; *std::regex_replace(&buf[0], first, last, rx, fmt) = '\0' ; std::cout << &buf[0] << std::endl; *std::regex_replace(&buf[0], first, last, rx, fmt, fonly) = '\0' ; std::cout << &buf[0] << std::endl; std::string str( "adaeaf" ); std::cout << std::regex_replace(str, rx, fmt) << std::endl; std::cout << std::regex_replace(str, rx, fmt, fonly) << std::endl; return 0; } |
输出如下：
[plain]
AxAyAz
Axayaz
AdAeAf
Adaeaf
C++ regex正则表达式的规则和其他编程语言差不多，如下：
特殊字符（用于匹配很难形容的字符）:
| characters | description | matches |
|---|---|---|
| . | not newline | any character except line terminators (LF, CR, LS, PS). |
| \t | tab (HT) | a horizontal tab character (same as \u0009). |
| \n | newline (LF) | a newline (line feed) character (same as \u000A). |
| \v | vertical tab (VT) | a vertical tab character (same as \u000B). |
| \f | form feed (FF) | a form feed character (same as \u000C). |
| \r | carriage return (CR) | a carriage return character (same as \u000D). |
| \cletter | control code | a control code character whose code unit value is the same as the remainder of dividing the code unit value of letter by 32. For example: \ca is the same as \u0001, \cb the same as \u0002, and so on... |
| \xhh | ASCII character | a character whose code unit value has an hex value equivalent to the two hex digits hh. For example: \x4c is the same as L, or \x23 the same as #. |
| \uhhhh | unicode character | a character whose code unit value has an hex value equivalent to the four hex digitshhhh. |
| \0 | null | a null character (same as \u0000). |
| \int | backreference | the result of the submatch whose opening parenthesis is the int-th (int shall begin by a digit other than 0). See groups below for more info. |
| \d | digit | a decimal digit character |
| \D | not digit | any character that is not a decimal digit character |
| \s | whitespace | a whitespace character |
| \S | not whitespace | any character that is not a whitespace character |
| \w | word | an alphanumeric or underscore character |
| \W | not word | any character that is not an alphanumeric or underscore character |
| \character | character | the character character as it is, without interpreting its special meaning within a regex expression. Any character can be escaped except those which form any of the special character sequences above. Needed for: ^ $ \ . * + ? ( ) [ ] { } | |
| [class] | character class | the target character is part of the class |
| [^class] | negated character class | the target character is not part of the class |
注意了，在C++反斜杠字符（\）会被转义
[cpp]
std::regex e1 ("\\d"); // \d -> 匹配数字字符
std::regex e2 ("\\\\"); // \\ -> 匹配反斜杠字符
数量：
| characters | times | effects |
|---|---|---|
| * | 0 or more | The preceding atom is matched 0 or more times. |
| + | 1 or more | The preceding atom is matched 1 or more times. |
| ? | 0 or 1 | The preceding atom is optional (matched either 0 times or once). |
| { int} | int | The preceding atom is matched exactly int times. |
| { int,} | int or more | The preceding atom is matched int or more times. |
| { min,max} | between min and max | The preceding atom is matched at least min times, but not more than max. |
注意了，模式 "(a+).*" 匹配 "aardvark" 将匹配到 aa，模式 "(a+?).*" 匹配 "aardvark" 将匹配到 a
组（用以匹配连续的多个字符）:
| characters | description | effects |
|---|---|---|
| (subpattern) | Group | Creates a backreference. |
| (?:subpattern) | Passive group | Does not create a backreference. |
注意了，第一种将创建一个反向引用，用于提取匹配到的内容，第二种则没有，相对来说性能方面也没这部分的开销
| characters | description | condition for match |
|---|---|---|
| ^ | Beginning of line | Either it is the beginning of the target sequence, or follows a line terminator. |
| $ | End of line | Either it is the end of the target sequence, or precedes a line terminator. |
| | | Separator | Separates two alternative patterns or subpatterns.. |
单个字符
[abc] 匹配 a, b 或 c.
[^xyz] 匹配任何非 x, y, z的字符范围
[a-z] 匹配任何小写字母 (a, b, c, ..., z). [abc1-5] 匹配 a, b , c, 或 1 到 5 的数字.c++ regex还有一种类POSIX的写法
| class | description | equivalent (with regex_traits, default locale) |
|---|---|---|
| [:alnum:] | alpha-numerical character | isalnum |
| [:alpha:] | alphabetic character | isalpha |
| [:blank:] | blank character | isblank |
| [:cntrl:] | control character | iscntrl |
| [:digit:] | decimal digit character | isdigit |
| [:graph:] | character with graphical representation | isgraph |
| [:lower:] | lowercase letter | islower |
| [:print:] | printable character | isprint |
| [:punct:] | punctuation mark character | ispunct |
| [:space:] | whitespace character | isspace |
| [:upper:] | uppercase letter | isupper |
| [:xdigit:] | hexadecimal digit character | isxdigit |
| [:d:] | decimal digit character | isdigit |
| [:w:] | word character | isalnum |
| [:s:] | whitespace character | isspace |
本文转自神ge 51CTO博客，原文链接:http://blog.51cto.com/12218412/1872058