test string for integer

[grcunning]

whats the best way to test a string to see if it is an integer?
I can loop through a string and use isdigit(), but that doesn't work if it is a negative number
I tried using atoi, but i get weird results
if I send it the string "1" it returns the integer 1
if I send it the string "-123" it returns the integer -123

but if i send it "123c4", it returns 123. i need that to return an error
if I send it "crft" or any string that doesn't start with a digit, it returns 0.

I just need to check a string, see if it contains an integer, and if so, assign it to an integer var, and if not, dont try to convert, but do some other stuff.

[PanGalactic]

Here is the absolute best way to do it in C++:

#include <boost/lexical_cast.hpp>

bool use_int(const std::string& s)
{
    try {
        int var = boost::lexical_cast<int>(s);
        // do stuff with var
    } catch (boost::bad_lexical_cast&) {
        // do other stuff because s is not an int
        return false;
    }
    return true;
}

boost::lexical_cast uses std::stringstream under the covers to do the conversions.