How to detect if atof or _wtof failes?

Question

How to detect if atof or _wtof failes to convert the string to double? But not by trying to check if the result is different form 0.0 because my input can be 0.0. Thanks!

Answer 1

Don't use atof. Instead, use strtod, from <cstdlib>, and also check errno from <cerrno>:

// assume: "char * mystr" is a null-terminated string

char * e;
errno = 0;
double x = std::strtod(mystring, &e);

if (*e != '\0' ||  // error, we didn't consume the entire string
    errno != 0 )   // error, overflow or underflow
{
    // fail
}

The pointer e points one past the last consumed character. You can also check e == mystr to see if any characters got consumed.

There's also std::wcstod for working with wchar_t-strings, from <cwstring>.

In C++11 you also have std::to_string/std::to_wstring, from <string>, but I believe that throws an exception if the conversion fails, which may not be a desirable failure mode when dealing with external data.