C++ String to Integer Conversion

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1

I’m working on a C++ program where I need to convert a string containing a numeric value into an integer. I want to ensure that this conversion is handled correctly and safely, especially when dealing with potential exceptions or invalid input.

Here’s a simplified example of what I’m trying to do:

#include <iostream>
#include <string>

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

    // How can I safely convert the string 'str' to an integer?

    int num = ???; // The converted integer should be stored here.

    std::cout << "Converted integer: " << num << std::endl;

    return 0;
}

In this code, I have a string str containing a numeric value. I want to convert this string into an integer variable num . However, I want to handle potential issues gracefully, such as cases where the string is not a valid integer. Could you offer a C++ code sample illustrating the proper and secure approach to convert a string to an integer while managing any potential exceptions or errors? I appreciate you helping me. I attempted to visit multiple sites like Scaler to locate the answer, but I was unable to do so. Thank you.

2

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
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3

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

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4

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. :sweat_smile:

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

  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++. :bulb:

  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). :+1:

  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. :thinking:

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

Adding additional links below to the documentation pages:

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