Inlining Question

Leslie Sanford

I want to define a set of constants without using macros. I'd like to determine whether these constants are floats or doubles at compile time. So I'm using templates. In my header file, I have this:

template<bool DoublePrecision>
struct Constants
{
typedef double SampleType;

static const double pi;
static const double piDoubled;
static const double SampleRateDefault;
static const double DenormalOffset;

};

template<>
struct Constants<false>
{
typedef float SampleType;

static const float pi;
static const float piDoubled;
static const float SampleRateDefault;
static const float DenormalOffset;

};

In my implementation file, I have this:

#include "Constants.h"

const double Constants<true>::pi = 3.14159265358979;
const double Constants<true>::piDoubled = Constants<true>::pi * 2.0;
const double Constants<true>::SampleRateDefault = 44100.0;
const double Constants<true>::DenormalOffset = 1.0E-25;

const float Constants<false>::pi = 3.141593f;
const float Constants<false>::piDoubled = 6.283185f;
const float Constants<false>::SampleRateDefault = 44100.0f;
const float Constants<false>::DenormalOffset = 1.0E-25f;

All of this compiles fine. My question is whether the values definined here will ultimately be inlined by the compiler where they are used. They are definined in one compilation unit but will be used in other compilation units. Will this prevent them from being inlined? In other words, will this ultimately be less efficient than using macros?

vikas amin

From design point of view Templates are better then macros ,

Vikas Amin UNITED STATES STEEL CORPORATION

My First Article on CP" Virtual Serial Port "[^]

modified on Thursday, July 24, 2008 5:33 PM

not_in_use

As far as I understand it they won't be inlined, just like regular constants. I have pretty much the same problem right now, except that I don't need to switch types. In this thread I posted my current idea for a workaround (using operator overloading and inline functions), maybe that could help you. It's a hack, but in theory it should work. As for your templating idea, if you don't need both float and double versions at the same time, you could just use typedefs like so:

// .h file
typedef double myFpType; // Changing this to float changes the type of all constants

const myFpType pi;
...

// .cpp file
const myFpType pi = myFpType( 3.14159265358979 );
...

or using my workaround idea from the link above:

typedef double myFpType;

// In .h file
INLINE_CONST( myFpType, pi, myFpType( 3.14159265358979 ) );

But maybe someone knows a better solution that could help us both out. Hope that helps, Peter