Строки и скобки в C++

#include <iostream>
#include <string>
 
int main(){
    std::string instr, outstr;
    std::cout << "Enter some text with one open and one close bracket:" << std::endl;
    std::getline(std::cin, instr);
    size_t start_pos = instr.find_first_of('(');
    if ( start_pos == std::string::npos ){
        std::cerr << "No open bracket!" << std::endl;
        return 1;
    }
    size_t end_pos = instr.find_last_of(')');
    if ( end_pos == std::string::npos ){
        std::cerr << "No close bracket!" << std::endl;
        return 1;
    }
    if ( start_pos > end_pos ){
        std::cerr << "Close bracket befor open bracked!" << std::endl;
        return 1;
    }
    if ( end_pos - start_pos < 2 ){
        std::cerr << "No symbols between brackets!" << std::endl;
        return 1;
    }
    outstr = instr.substr(start_pos + 1, end_pos - start_pos - 1);
    std::cout << "Inside brackets: " << outstr << std::endl;
 
    return 0;
}