Thread: determining if an integer is a legal integer

  1. #1
    Registered User
    Join Date
    Oct 2005

    determining if an integer is a legal integer

    I have a very simple question that I have not been able to find the answer to anywhere. How do you determine if an integer is a legal integer value? Thanks.

  2. #2
    Registered User
    Join Date
    Sep 2001
    Well it depends on what exactly you're doing. If you try to assign the string "Hello World!" to an int, you'll get a compiler error. If you read in a character, and want to know if an integer was entered, you could check the data using the isdigit() funcion in <cctype>.

  3. #3
    Registered User
    Join Date
    Jan 2005
    Your question is vague, but there was just a thread about this:

    Here is the final version of my code that works on a string input and handles negative numbers, overflow, octal and hex input, etc.
    #include <sstream>
    #include <string>
    bool is_int(const std::string& s)
        int i;
        std::istringstream istr(s);
        if (!(istr >> i))
            return false;
        return istr.rdbuf()->in_avail() == 0;

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