Question

I’m writing a Ruby C Extension where I’m using math.h. It’s being compiled on both OSX and Windows. Under Windows I use nmake that comes with Visual Studio Express C++ 2010.

I found that VS didn’t include the round() function in their math.h. So I added this to compensate:

static inline double round( double value )
{    
  return floor( value + 0.5 );
}

That off course caused an error when compiling under OSX as round() there is defined. (The actual error I think was that I’d declared mine static after it’s already been declared a non-static version.

Regardless, I’d like to avoid redefining the function if it does exist.

At the moment I have this conditional:

#ifdef _WIN32
static inline double round( double value )
{    
  return floor( value + 0.5 );
}
#endif

That worked in my scenario – but it seem a bit generic. I mean, what if I compile with a different compiler under Windows?

So my question is, can I detect if a function is already defined, and then avoid defining it myself?

Or, can I detect specifically the compiler nmake use – cl I think it is?

I’m thinking I’d ideally be able to detect if the function is already defined, as it seem like the most robust method.

Answer 1

I found that Ruby’s mkmf utility has a method have_func that one can use to check for the existence of functions: http://apidock.com/ruby/Object/have_func

I added have_func( 'round', 'math.h' ) to my extconf.rb file which then gave me a HAVE_ROUND preprocessor constant.

Then I could safely define round() myself it it didn’t exist:

#ifndef HAVE_ROUND
static inline double round( double value )
{    
  return floor( value + 0.5 );
}
#endif

Worked perfectly! 🙂