c ++ regex使用regex_search()提取所有子字符串

Question

我是c ++正则表达式的新手.我有一个字符串"{1,2,3}",我想提取数字1 2 3.我认为我应该使用regex_search但它失败了.

#include<iostream>
#include<regex>
#include<string>
using namespace std;
int main()
{
        string s1("{1,2,3}");
        string s2("{}");
        smatch sm;
        regex e(R"(\d+)");
        cout << s1 << endl;
        if (regex_search(s1,sm,e)){
                cout << "size: " << sm.size() << endl;
                for (int i = 0 ; i < sm.size(); ++i){
                        cout << "the " << i+1 << "th match" <<": "<< sm[i] <<  endl;
                }
        }
}

结果:

{1,2,3}
size: 1
the 1th match: 1

Answer 1

std :: regex_search仅在找到第一个匹配后返回.

什么性病:: SMATCH给你的是所有在正则表达式匹配的组.您的正则表达式只包含一个组,因此std :: smatch只包含一个项目.

如果要查找所有匹配项,则需要使用std :: sregex_iterator.

int main()
{
    std::string s1("{1,2,3}");
    std::regex e(R"(\d+)");

    std::cout << s1 << std::endl;

    std::sregex_iterator iter(s1.begin(), s1.end(), e);
    std::sregex_iterator end;

    while(iter != end)
    {
        std::cout << "size: " << iter->size() << std::endl;

        for(unsigned i = 0; i < iter->size(); ++i)
        {
            std::cout << "the " << i + 1 << "th match" << ": " << (*iter)[i] << std::endl;
        }
        ++iter;
    }
}

输出:

{1,2,3}
size: 1
the 1th match: 1
size: 1
the 1th match: 2
size: 1
the 1th match: 3

该end迭代器是由设计建造默认值,以便它等于iter时iter已经用完了比赛.注意我在循环的底部++iter.这将iter继续下一场比赛.当没有更多匹配时,iter具有与默认构造相同的值end.

显示子匹配(捕获组)的另一个示例:

int main()
{
    std::string s1("{1,2,3}{4,5,6}{7,8,9}");
    std::regex e(R"~((\d+),(\d+),(\d+))~");

    std::cout << s1 << std::endl;

    std::sregex_iterator iter(s1.begin(), s1.end(), e);
    std::sregex_iterator end;

    while(iter != end)
    {
        std::cout << "size: " << iter->size() << std::endl;

        std::cout << "expression match #" << 0 << ": " << (*iter)[0] << std::endl;
        for(unsigned i = 1; i < iter->size(); ++i)
        {
            std::cout << "capture submatch #" << i << ": " << (*iter)[i] << std::endl;
        }
        ++iter;
    }
}

输出:

{1,2,3}{4,5,6}{7,8,9}
size: 4
expression match #0: 1,2,3
capture submatch #1: 1
capture submatch #2: 2
capture submatch #3: 3
size: 4
expression match #0: 4,5,6
capture submatch #1: 4
capture submatch #2: 5
capture submatch #3: 6
size: 4
expression match #0: 7,8,9
capture submatch #1: 7
capture submatch #2: 8
capture submatch #3: 9