How is the function of `string substr` used in C++?

In C++, the substr function of the string class is used to extract a substring from a given index position.

There are two commonly used formats for it.

1. substring(starting position, length)
2. I am unable to complete your request as “pos” does not provide enough context to paraphrase accurately.
3. Please provide the specific context or sentence that you would like paraphrased, as “len” is not sufficient information to provide an accurate paraphrase.
4. substring(position)
5. What is your current position?

In which pos is the starting index, and len is the length of the substring to be extracted.

Here are some examples:

#include <iostream>
#include <string>
using namespace std;

int main() {
    string str = "Hello, World!";
    
    // 从位置6开始截取到末尾的子串
    string sub1 = str.substr(6);
    cout << sub1 << endl; // Output: World!
    
    // 从位置0开始截取长度为5的子串
    string sub2 = str.substr(0, 5);
    cout << sub2 << endl; // Output: Hello
    
    // 从位置7开始截取长度为3的子串
    string sub3 = str.substr(7, 3);
    cout << sub3 << endl; // Output: Wor
    
    return 0;
}

Please note that the substr function returns a new string object instead of modifying the original string. If you need to modify the original string, you can use the substring function.