Question

I use the boost lexical_cast library for parsing text data into numeric values quite often. In several situations however, I only need to check if values are numeric; I don’t actually need or use the conversion.

So, I was thinking about writing a simple function to test if a string is a double:

template<typename T> 
bool is_double(const T& s)
{
  try 
  {
    boost::lexical_cast<double>(s); 
    return true;
  }
  catch (...) 
  {
    return false;
  }
}

My question is, are there any optimizing compilers that would drop out the lexical_cast here since I never actually use the value?

Is there a better technique to use the lexical_cast library to perform input checking?

Answer 1

Since the cast might throw an an exception, a compiler that would just drop that cast would be seriously broken. You can assume that all major compilers will handle this correctly.

Trying to to do the lexical_cast might not be optimal from a performance point of view, but unless you check millions of values this way it won’t be anything to worry about.