Question

I’m very new to C++, boost etc.

I would like to know if there is already a function in boost or STL I can use to determine if a string is numeric.

Numeric strings may look like:
100

or

100.52

I know there are tons of examples how to write such a function but I would like to know if there is already a function I can use for this.

I’m looking for a pure C++-solution, not C.

[UPDATE:
I’m already using lexical_cast to convert my strings, I’m just wondering if there is a method like is_numeric I can use for this…]

Answer 1

No, there’s not a ready-made way to do this directly.

You could use boost::lexical_cast<double>(your_string) or std::stod(your_string) and if it throws an exception then your string is not a double.

C++11:

    bool is_a_number = false;
    try
    {
        std::stod(your_string);
        is_a_number = true;
    }
    catch(const std::exception &)
    {
        // if it throws, it's not a number.
    }

Boost:

    bool is_a_number = false;
    try
    {
        lexical_cast<double>(your_string);
        is_a_number = true;
    }
    catch(bad_lexical_cast &)
    {
        // if it throws, it's not a number.
    }