如何检查C++ std :: string是否以某个字符串开头,并将子字符串转换为int？

#include<iostream>
#include<string>
#include <stdexcept>

int main() {
    std::string main_str = "12345";
    std::string prefix_str = "12";

    if (main_str.find(prefix_str) == 0) {
        std::cout << "The main string starts with the prefix string."<< std::endl;
        try {
            int result = std::stoi(main_str.substr(prefix_str.length()));
            std::cout << "The converted integer is: "<< result<< std::endl;
        } catch (std::invalid_argument &e) {
            std::cout << "Invalid argument: " << e.what()<< std::endl;
        } catch (std::out_of_range &e) {
            std::cout << "Out of range: " << e.what()<< std::endl;
        }
    } else {
        std::cout << "The main string does not start with the prefix string."<< std::endl;
    }

    return 0;
}