inline function declaration

[Hunter2]

Hi, just a quick question. I'm running MSVC, and in my code, I have a header called CGeom.h:

#ifndef (...)
#define (...)

inline float degreesToRadians(float degrees);

#endif

In CGeom.cpp, I have the function definition for degreesToRadians:

inline float degreesToRadians(float degrees)
{
     //do something
     return (result);
}

When I compiled this with the debug settings, it worked fine; under Release build, I got a unresolved external symbol for degreesToRadians. The problem went away when I just merged the definition and prototype(?) together in the header, instead of having them separate.

Can anybody tell me why this happens?

[MrWizard]

inline functions in C++ have internal linkage. You need to put the definition in the declaration in the .h file. A common way to do this is by putting all of your class declarations in the header and then at the end of the header putting #include "math.inl" and have all of your inline code in there. This isn't standard or anything but a lot of people do it. Hope this clears it up.

[Hunter2]

Thanks MrWizard, my confusion is no more

[Wledge]

Originally posted by MrWizard
inline functions in C++ have internal linkage.

No,
7.1.2 Function Specifiers,Footnote 79

The inline keyword has no effect on the linkage of a function.

So they have the linkage they'd if inline was not specified. Linkage is always defined, the three choices are internal, external, or no linkage. An inline function with no explicit linkage spec has external linkage.

[Hunter2]

Oh, great. So what's the problem then?

[MrWizard]

Well the new C++ standard says it has no effect. The old C++ standard says it has internal linkage. Guess which standard the old compilers go by.