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说明: 如果以前懂正则, 那么regex就只是了解语法, 和cpp的差异;
头文件
#include regex参考链接
https://en.cppreference.com/w/cpp/regex
几大要素
被匹配串: 字符串, 三种指定方式 – 迭代器, \0结尾的字符串, std::string;匹配正则: std::basic…正则表达式库
说明: 如果以前懂正则, 那么regex就只是了解语法, 和cpp的差异;
头文件
#include regex参考链接
https://en.cppreference.com/w/cpp/regex
几大要素
被匹配串: 字符串, 三种指定方式 – 迭代器, \0结尾的字符串, std::string;匹配正则: std::basic_regex类型, std::regex则是std::basic_regexchar的别名;匹配结果: std::match_results;替换表达式: 字符串, 决定如何对匹配内容进行替换;
正则和结果
正则表达式类: std::basic_regex
匹配结果类: std::match_results
匹配结果组: ()生成的组std::sub_match, 继承自std::pair, 存储一对迭代器, 而不是string; std::match_results::begin使用;
关联算法
regex_match: 正则匹配整个字符串;
regex_search: 正则匹配子串;
regex_replace: 将匹配内容按照指定规则进行替换;
迭代器
regex_iterator: 规则搜索所有匹配串;
regex_token_iterator: 迭代所有组;
异常
regex_error: 正则表达式非法
选项
syntax_option_type: 使用正则版本, 是否区分大小写之类;
match_flag_type: 匹配行为控制
正则表达式
类的声明
templateclass CharT,class Traits std::regex_traitsCharTclass basic_regex;CharT数据类型;
typedef
std::regex std::basic_regexchar
std::wregex std::basic_regexwchar_t常用的regex就是别名;
构造
构造函数
// 默认构造
basic_regex(); // (1) (since C11)// 使用 \0 结尾的字符串作为正则表达式, f 表示使用正则方案, egrep, extended, ecmascript 等
explicit basic_regex(const CharT *s,flag_type f std::regex_constants::ECMAScript); // (2) (since C11)// 使用字符串 s 的前 n 个作为正则, (aa)bcd, 4 即 (aa) 作为正则
basic_regex(const CharT *s, std::size_t count,flag_type f std::regex_constants::ECMAScript); // (3) (since C11)// 拷贝其他正则;
basic_regex(const basic_regex other); // (4) (since C11)// 右值运算, 清空 other 正则;
basic_regex(basic_regex other) noexcept; // (5) (since C11)// basic_string类型, 并萃取其基本类型; 常用 std::string 即 std::basic_stringchar
template class ST, class SA
explicit basic_regex(const std::basic_stringCharT, ST, SA str,flag_type f std::regex_constants::ECMAScript); // (6) (since C11)// 使用迭代器进行初始化;
template class ForwardIt
basic_regex(ForwardIt first, ForwardIt last,flag_type f std::regex_constants::ECMAScript); // (7) (since C11)// 使用列表进行初始化; {a, b, c}; 这种;
basic_regex(std::initializer_listCharT init,flag_type f std::regex_constants::ECMAScript); //(8) (since C11)异常: 构造函数可能抛出异常
1. 可能异常, 和实现有关
2. std::regex_error 如果正则非法就会抛出;
3. std::regex_error 如果正则非法就会抛出;
4. 可能异常, 和实现有关
5. 可能异常, 和实现有关
6. std::regex_error 如果正则非法就会抛出;
7. std::regex_error 如果正则非法就会抛出;
8. std::regex_error 如果正则非法就会抛出;正则完全匹配
被匹配串是否完全匹配整个正则表达式
构造
函数原型: 返回值是否匹配, (链表 指针 std::sring) * (返回结果 不返回结果) 6 种, 1 delte 类型;
// BidirIt 双向链表;
// [first, last) 指定搜索串;
// m 获取搜索结果
// e 正则表达式对象
// flags 匹配额外补充
template class BidirIt,class Alloc, class CharT, class Traits
bool regex_match(BidirIt first, BidirIt last,std::match_resultsBidirIt, Alloc m,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(1) (since C11)// 和 (1) 类似, 但是不要结果
template class BidirIt,class CharT, class Traits
bool regex_match(BidirIt first, BidirIt last,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(2) (since C11)// 字符串指定匹配串, 输出结果到 m
template class CharT, class Alloc, class Traits
bool regex_match(const CharT *str,std::match_resultsconst CharT *, Alloc m,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(3) (since C11)// std::string 类型, 输出结果到 m
template class STraits, class SAlloc,class Alloc, class CharT, class Traits
bool regex_match(const std::basic_stringCharT, STraits, SAlloc s,std::match_resultstypename std::basic_stringCharT, STraits, SAlloc::const_iterator,Alloc m,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(4) (since C11)// 字符串指定匹配串, 不输出结果;
template class CharT, class Traits
bool regex_match(const CharT *str,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); // (5) (since C11)// std::string 指定匹配串, 不输出结果;
template class STraits, class SAlloc,class CharT, class Traits
bool regex_match(const std::basic_stringCharT, STraits, SAlloc s,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(6) (since C11)// 临时的 string 对象不支持; 即右值;
template class STraits, class SAlloc,class Alloc, class CharT, class Traits
bool regex_match(const std::basic_stringCharT, STraits, SAlloc ,std::match_resultstypename std::basic_stringCharT, STraits, SAlloc::const_iterator,Alloc ,const std::basic_regexCharT, Traits ,std::regex_constants::match_flag_type flags std::regex_constants::match_default) delete; //(7) (since C11)返回值
函数返回值
true匹配, false不匹配
std::match_results: 执行后不管成功与否都会修改;
# If the match does not exist:
m.ready() true
m.empty() true
m.size() 0
# If the match exists:
m.ready() true
m.empty() false
m.size() number of marked subexpressions plus 1, that is, 1 e.mark_count()# 用迭代器表示匹配部分前的结果; 比字符串或std::string更灵活;
m.prefix().first first
m.prefix().second first
m.prefix().matched false (the match prefix is empty)# 匹配的后面字符串
m.suffix().first last
m.suffix().second last
m.suffix().matched false (the match suffix is empty)# 0 表示整个串
m[0].first first
m[0].second last
m[0].matched true (the entire sequence is matched)# n 0 则表示第 n 个组;
m[n].first the start of the sequence that matched marked sub-expression n, or last if the subexpression did not participate in the match
m[n].second the end of the sequence that matched marked sub-expression n, or last if the subexpression did not participate in the match
m[n].matched true if sub-expression n participated in the match, false otherwise# 具体可了解 match_results 类, 重载了 operator , 可以直接输出;正则搜索
声明
// BidirIt 双向链表
// 使用 frist, last 提供的字符串, e 的正则, m 输出结果
templateclass BidirIt,class Alloc, class CharT, class Traits bool
regex_search(BidirIt first, BidirIt last,std::match_resultsBidirIt, Alloc m,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(1) (since C11)// 同一, 使用字符串指定;
template class CharT, class Alloc, class Traits
bool regex_search(const CharT *str,std::match_resultsconst CharT *, Alloc m,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(2) (since C11)// 同上使用 std::string 指定字符串
template class STraits, class SAlloc,class Alloc, class CharT, class Traits
bool regex_search(const std::basic_stringCharT, STraits, SAlloc s,std::match_resultstypename std::basic_stringCharT, STraits, SAlloc::const_iterator,Alloc m,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(3) (since C11)// 同一, 但不输出结果
template class BidirIt,class CharT, class Traits
bool regex_search(BidirIt first, BidirIt last,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(4) (since C11)// 同二, 但不输出结果
template class CharT, class Traits
bool regex_search(const CharT *str,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(5) (since C11)
template class STraits, class SAlloc,class CharT, class Traits// 同三, 但不输出结果
bool regex_search(const std::basic_stringCharT, STraits, SAlloc s,const std::basic_regexCharT, Traits e,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(6) (since C11)// 同三, 不支持右值;
template class STraits, class SAlloc,class Alloc, class CharT, class Traits
bool regex_search(const std::basic_stringCharT, STraits, SAlloc ,std::match_resultstypename std::basic_stringCharT, STraits, SAlloc::const_iterator,Alloc ,const std::basic_regexCharT, Traits ,std::regex_constants::match_flag_type flags std::regex_constants::match_default) delete; //(7) (since C11)
返回结果: m
If the match does not exist:
m.ready() true
m.empty() true
m.size() 0
If the match exists:
m.ready() true
m.empty() false
m.size() number of marked subexpressions plus 1, that is, 1 e.mark_count()
m.prefix().first first
m.prefix().second m[0].first
m.prefix().matched m.prefix().first ! m.prefix().second
m.suffix().first m[0].second
m.suffix().second last
m.suffix().matched m.suffix().first ! m.suffix().second
m[0].first the start of the matching sequence
m[0].second the end of the matching sequence
m[0].matched true
m[n].first the start of the sequence that matched marked sub-expression n, or last if the subexpression did not participate in the match
m[n].second the end of the sequence that matched marked sub-expression n, or last if the subexpression did not participate in the match
m[n].matched true if sub-expression n participated in the match, false otherwise正则替换
声明
// OutputIt 输出迭代器, 并输出首地址;
// BidirIt 双向链表
// 使用 frist, last 提供的字符串, re 的正则
// fmt 使用 std::string 指定
template class OutputIt, class BidirIt,class Traits, class CharT,class STraits, class SAlloc
OutputIt regex_replace(OutputIt out, BidirIt first, BidirIt last,const std::basic_regexCharT, Traits re,const std::basic_stringCharT, STraits, SAlloc fmt,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(1) (since C11)// 同上 fmt 用 字符串指定;
template class OutputIt, class BidirIt,class Traits, class CharT
OutputIt regex_replace(OutputIt out, BidirIt first, BidirIt last,const std::basic_regexCharT, Traits re,const CharT *fmt,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(2) (since C11)// 同一: 输出结果为字符串而不是迭代器;
// fmt 用 std::string 指定;
template class Traits, class CharT,class STraits, class SAlloc,class FTraits, class FAlloc
std::basic_stringCharT, STraits, SAlloc
regex_replace(const std::basic_stringCharT, STraits, SAlloc s,const std::basic_regexCharT, Traits re,const std::basic_stringCharT, FTraits, FAlloc fmt,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(3) (since C11)// 同上, fmt 用字符串指定;
template class Traits, class CharT,class STraits, class SAlloc
std::basic_stringCharT, STraits, SAlloc
regex_replace(const std::basic_stringCharT, STraits, SAlloc s,const std::basic_regexCharT, Traits re,const CharT *fmt,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(4) (since C11)// s 用 字符串指定, 输出为 basic_string, fmt 为 std::basic_string
template class Traits, class CharT,class STraits, class SAlloc
std::basic_stringCharT
regex_replace(const CharT *s,const std::basic_regexCharT, Traits re,const std::basic_stringCharT, STraits, SAlloc fmt,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(5) (since C11)// 同上, fmt用 字符串指定;
template class Traits, class CharT
std::basic_stringCharT
regex_replace(const CharT *s,const std::basic_regexCharT, Traits re,const CharT *fmt,std::regex_constants::match_flag_type flags std::regex_constants::match_default); //(6) (since C11)差异点:
替换主串: 迭代器, std::basic_string, CharT 型;fmt格式: std::basic_string, CharT;
fmt
说明
$ or $0 is used to insert the whole regex match.
#include regex
#include iostreamint main () {std::cout std::regex_replace(hello, im xiaoli, std::regex(.), $0!!) std::endl;
}$ g test.cpp ./a.out
hello, im xiaoli!!$1, $2, … up to $9 is used to insert the text matched by the first nine capturing groups.
#include regex
#include iostreamint main () {std::cout std::regex_replace(hello, im xiaoli, std::regex((hello, im )(\\w)), $1 xiaowang) std::endl;
}$ g test.cpp ./a.out
hello, im xiaowang$ (back-tick) is used to insert the string that is left of the match.
#include regex
#include iostreamint main () {std::cout std::regex_replace(hello, im xiaoli, std::regex(), \n$\n) std::endl;
}即正则表达式匹配串(不包含匹配字符串本身)左边的内容;
$ hello, i$ g test.cpp ./a.out
hello, i
hello, i
m xiaoli$’ (quote) is used to insert the string that is right of the match.
#include regex
#include iostreamint main () {std::cout std::regex_replace(hello, im xiaoli, std::regex(), \n$\n) std::endl;
}同样的道理, 是去除匹配串后的右边串;
$ g test.cpp ./a.out
hello, i
m xiaoli
m xiaoliIf number of capturing group is less than the requested, then that will be replaced by nothing.
参考链接
https://www.geeksforgeeks.org/regex_replace-in-cpp-replace-the-match-of-a-string-using-regex_replace/
regex_iterator
和regex_search一样; 只是match_results变为iter;
只输出匹配
案例
#include iostream
#include iterator
#include regex
#include stringint main()
{const std::string s Quick brown fox.;std::regex words_regex([^\\s]);auto words_begin std::sregex_iterator(s.begin(), s.end(), words_regex);auto words_end std::sregex_iterator();std::cout Found std::distance(words_begin, words_end) words:\n;for (std::sregex_iterator i words_begin; i ! words_end; i){std::smatch match *i;std::string match_str match.str();std::cout match_str \n;}
}Found 3 words:
Quick
brown
fox.regex_token_iterator
说明: 只获取组
案例
#include algorithm
#include fstream
#include iostream
#include iterator
#include regexint main()
{// Tokenization (non-matched fragments)// Note that regex is matched only two times; when the third value is obtained// the iterator is a suffix iterator.const std::string text Quick brown fox.;const std::regex ws_re(\\s); // whitespacestd::copy(std::sregex_token_iterator(text.begin(), text.end(), ws_re, -1),std::sregex_token_iterator(),std::ostream_iteratorstd::string(std::cout, \n));std::cout \n;// Iterating the first submatchesconst std::string html R(pa hrefhttp://google.comgoogle/a )R( a HREF http://cppreference.comcppreference/a\n/p);const std::regex url_re(R!!(\s*A\s[^]*href\s*\s*([^]*))!!, std::regex::icase);std::copy(std::sregex_token_iterator(html.begin(), html.end(), url_re, 1),std::sregex_token_iterator(),std::ostream_iteratorstd::string(std::cout, \n));
}Quick
brown
fox.http://google.com
http://cppreference.com
