原文 2014-02-09 19:32:01 发表于 CSDN，这里对以前写的文章做下收录。
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regex_match
// regex_match example
#include <iostream>
#include <string>
#include <regex>
int main (){
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 object matched\n";
if ( std::regex_match ( s.begin(), s.end(), e ) )
std::cout << "range matched\n";
std::cmatch cm; // same as std::match_results<const char*> cm;
std::regex_match ("subject",cm,e);
std::cout << "string literal with " << cm.size() << " matches\n";
std::smatch sm; // same as std::match_results<string::const_iterator> sm;
std::regex_match (s,sm,e);
std::cout << "string object with " << sm.size() << " matches\n";
std::regex_match ( s.cbegin(), s.cend(), sm, e);
std::cout << "range with " << sm.size() << " matches\n";
// using explicit flags:
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[i] << "] ";
}
std::cout << std::endl;
return 0;
}
输出如下：
string literal matched
string object matched
range matched
string literal with 3 matches
string object with 3 matches
range with 3 matches
the matches were: [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regex_search
// 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：
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
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regex_replace
// regex_replace example
#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：
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
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 |
参考：
http://www.cplusplus.com/reference/regex/