C++中的regex_replace |使用regex_replace替换字符串的匹配项

std :: regex_replace()用于替换字符串的所有匹配项，

句法：

regex_replace(subject, regex_object, replace_text)

参数：它接受以下三个参数：

1. 主题字符串作为第一个参数。
2. 正则表达式对象作为第二个参数。
3. 以替换文本作为第三个参数的字符串。

返回值：函数返回一个新的字符串，其中包含替换内容。

1. $＆或$ 0用于插入整个正则表达式匹配项。
2. $ 1，$ 2，…最多$ 9用于插入与前9个捕获组匹配的文本。
3. $`(反引号)用于插入匹配项左侧的字符串。
4. $’(引号)用于插入匹配项右边的字符串。
5. 如果捕获组的数量小于请求的数量，则将其替换为任何内容。

例子：
假设创建了一个正则表达式对象re(“(geeks)(。*)”) ，并且主题字符串为： subject(“关于geeksforgeeks的全部”) ，您希望将匹配项替换为任何捕获组的内容(例如$ 0)。 ，$ 1，…最多9)。

Example-1:
Replace the match by the content of $1.
Here match is “geeksforgeeks” that will be replaced by $1(“geeks”).
Hence, result “its all about geeks”.

Example-2:
Replace the match by the content of $2.
Here match is “geeksforgeeks” that will be replaced by $2(“forgeeks”).
Hence, result “its all about forgeeks”.

下面是显示regex_replace的程序。

// C++ program to show the working
// of regex_replace
#include 
using namespace std;
  
int main()
{
    string subject("its all about geeksforgeeks");
  
    string result1, result2, result3, result4;
    string result5;
  
    // regex object
    regex re("(geeks)(.*)");
  
    // $2 contains, 2nd capturing group which is (.*) means
    // string after "geeks" which is "forgeeks". hence
    // the match(geeksforgeeks) will be replaced by "forgeeks".
    // so the result1 = "its all about forgeeks"
    result1 = regex_replace(subject, re, "$2");
  
    // similarly $1 contains, 1 st capturing group which is
    // "geeks" so the match(geeksforgeeks) will be replaced
    // by "geeks".so the result2 = "its all about geeks".
    result2 = regex_replace(subject, re, "$1");
  
    // $0 contains the whole match
    // so result3 will remain same.
    result3 = regex_replace(subject, re, "$0");
  
    // $0 and $& contains the whole match
    // so result3 will remain same
    result4 = regex_replace(subject, re, "$&");
  
    // Here number of capturing group
    // is 2 so anything above 2
    // will be replaced by nothing.
    result5 = regex_replace(subject, re, "$6");
  
    cout << result1 << endl << result2 << endl;
    cout << result3 << endl << result4 << endl
         << result5;
  
    return 0;
}

输出：

its all about forgeeks
its all about geeks
its all about geeksforgeeks
its all about geeksforgeeks
its all about

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