How to determine if a string is a number with C++?

Question

I\'ve had quite a bit of trouble trying to write a function that checks if a string is a number. For a game I am writing I just need to check if a line from the file I am r

Answer 1

Why reinvent the wheel? The C standard library (available in C++ as well) has a function that does exactly this:

char* p;
long converted = strtol(s, &p, 10);
if (*p) {
    // conversion failed because the input wasn't a number
}
else {
    // use converted
}

If you want to handle fractions or scientific notation, go with strtod instead (you'll get a double result).

If you want to allow hexadecimal and octal constants in C/C++ style ("0xABC"), then make the last parameter 0 instead.

Your function then can be written as

bool isParam(string line)
{
    char* p;
    strtol(line.c_str(), &p, 10);
    return *p == 0;
}