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std::basic_regex<CharT,Traits>:: mark_count

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std::basic_regex
unsigned mark_count ( ) const ;
(自 C++11 起)

返回正则表达式中已标记子表达式（也称为捕获组）的数量。

目录

参数

(无)

返回值

正则表达式内标记的子表达式数量。

异常

可能抛出实现定义的异常。

示例

运行此代码 
#include <iostream>
#include <regex>
int main()
{    
    std::regex r1{"abcde"};
    std::cout << "r1 has " << r1.mark_count() << " subexpressions" << '\n';
    // 预期：0
    std::regex r2{"ab(c)de"};
    std::cout << "r2 has " << r2.mark_count() << " subexpressions" << '\n';
    // 预期：1
    std::regex r3{"a(bc)d(e)"}; 
    std::cout << "r3 has " << r3.mark_count() << " subexpressions" << '\n';
    // 预期：2
    // 嵌套子表达式
    std::regex r4{"abc(de(fg))"};
    std::cout << "r4 has " << r4.mark_count() << " subexpressions" << '\n';
    // 预期：2
    // 转义括号
    std::regex r5{"a(bc\\(\\)de)"};
    std::cout << "r5 has " << r5.mark_count() << " subexpressions" << '\n';
    // 预期：1
    // 使用 nosubs 标志
    std::regex r6{"ab(c)de", std::regex_constants::nosubs};
    std::cout << "r6 has " << r6.mark_count() << " subexpressions" << '\n';
    // 预期：0
}

输出： 

r1 has 0 subexpressions
r2 has 1 subexpressions
r3 has 2 subexpressions
r4 has 2 subexpressions
r5 has 1 subexpressions
r6 has 0 subexpressions