Well, I can see some logical issues with your code.
Can you try this code and confirm wether it is working or not.

#include <iostream>
#include <string>
#include <stdexcept> // Include this for std::invalid_argument and std::out_of_range

int main() {
    std::string str = "12345"; // This could be any numeric string.

    int num = 0; // The converted integer will be stored here.

    try {
        num = std::stoi(str);
        std::cout << "Converted integer: " << num << std::endl;
    } catch (const std::invalid_argument& e) {
        std::cerr << "Invalid argument: " << e.what() << std::endl;
    } catch (const std::out_of_range& e) {
        std::cerr << "Out of range: " << e.what() << std::endl;
    }

    return 0;
}

Thanks

I’m not a senior C++ developer, so I have no idea about the best way, but this should work:

#include <iostream>
#include <string>
#include <cctype>

int main() {
  std::string str = "123";
  // str[0] - gets the first character
  // isdigit(character) - checks if character is a digit
  // stoi throws invalid_argument exception
  // if string does not start with a digit
  if (isdigit(str[0])) {
    /*
    stoi means "String TO Integer"
    you can easily change it to for example:
      * stof ("String TO Float"),
      * stol ("String TO Long")
      * and so on …
    */
    int num = std::stoi(str);
    std::cout << "[DONE] Converted integer: " << num << std::endl;
  } else {
    std::cout << "[ERROR] Invalid input string: " << str << std::endl;
  }

  return 0;
}

Helpful resources

1. Reference : string : stoi
2. Reference : cctype : isdigit

For me looks good. I have tested it on my MX Linux distribution.

It’s interesting how much the code says about it’s author. In my case 7 years in Elixir gives result …

1. Even if somehow I remember somewhat about try/catch I was still looking for a “better” solution, so I have added one extra dependency for a single isdigit call.

2. std:err of course! When I saw your code I have reminded it immediately.

3. stdexcept is interesting. Maybe I have used it, but I don’t remember it much especially e.what() call. I guess that I haven’t used multiple catch blocks before in C++.

4. out_of_range error handling is simple, but also brilliant idea. I’m not surprised that I wasn’t thinking about such edge case since in Elixir we have just Integer for all well … integers (no small or big ones).

5. I only wonder why you define num variable outside of try block having in mind it’s only usage is within it, but that’s definitely not the most important thing.

So much to learn in such a small code, thanks!

Adding additional links below to the documentation pages:

1. Reference : stdexcept : invalid_argument
2. Reference : stdexcept : out_of_range