C++ IsFloat function

Question

Does anybody know of a convenient means of determining if a string value \"qualifies\" as a floating-point number?

bool IsFloat( string MyString )
{
   ... e         


        

Answer 1

I always liked strtof since it lets you specify an end pointer.

bool isFloat(const std::string& str)
{
    char* ptr;
    strtof(str.c_str(), &ptr);
    return (*ptr) == '\0';
}

This works because the end pointer points to the character where the parse started to fail, therefore if it points to a nul-terminator, then the whole string was parsed as a float.

I'm surprised no one mentioned this method in the 10 years this question has been around, I suppose because it is more of a C-Style way of doing it. However, it is still perfectly valid in C++, and more elegant than any stream solutions. Also, it works with "+inf" "-inf" and so on, and ignores leading whitespace.

EDIT

Don't be caught out by empty strings, otherwise the end pointer will be on the nul-termination (and therefore return true). The above code should be:

bool isFloat(const std::string& str)
{
    if (str.empty())
        return false;

    char* ptr;
    strtof(str.c_str(), &ptr);
    return (*ptr) == '\0';
}