Thread: 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.

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>.

Your question is vague, but there was just a thread about this:

http://cboard.cprogramming.com/showthread.php?t=70234

Here is the final version of my code that works on a string input and handles negative numbers, overflow, octal and hex input, etc.

Code:

#include <sstream>
#include <string>

bool is_int(const std::string& s)
{
    int i;
    std::istringstream istr(s);
    istr.unsetf(std::ios::dec);
    if (!(istr >> i))
        return false;

    return istr.rdbuf()->in_avail() == 0;
}