Is there a TryParse equivalent in C++ (gcc)?

Question

Is there a equivalent of TryParse in C++(gcc) ?

I would like to parse a string which may contain (+31321) and store it as long. I know phone numbers are stored as st

Answer 1

The trouble with strtoul() and family there is no real way to test for failure.
If it fails to parse then it returns 0 without setting errno (which is only set on overflow).

boost lexical cast

#include 


int main()
{
    try
    {
        long x = boost::lexical_cast("+1234");
        std::cout << "X is " << x << "\n";
    }
    catch(...)
    {
        std::cout << "Failed\n";
    }
}

Doing it using streams

int main()
{
    try
    {
        std::stringstream stream("+1234");
        long x;
        char test;

        if ((!(stream >> x)) || (stream >> test))
        {
            // You should test that the stream into x worked.
            // You should also test that there is nothing left in the stream
            //    Above: if (stream >> test) is good then there was content left after the long
            //           This is an indication that the value you were parsing is not a number.
            throw std::runtime_error("Failed");
        }
        std::cout << "X is " << x << "\n";
    }
    catch(...)
    {
        std::cout << "Failed\n";
    }
}

Using scanf:

int main()
{
    try
    {
        char integer[] = "+1234";
        long x;
        int  len;

        if (sscanf(integer, "%ld%n", &x, &len) != 1 || (len != strlen(integer)))
        {
            // Check the scanf worked.
            // Also check the scanf() read everything from the string.
            // If there was anything left it indicates a failure.
            throw std::runtime_error("Failed");
        }
        std::cout << "X is " << x << "\n";
    }
    catch(...)
    {
        std::cout << "Failed\n";
    }
}