I was reading opengl es book and in the source code i found this Macro
/// // Macros // #define ESUTIL_API #define ESCALLBACK later in the implementation file .c
void ESUTIL_API esInitContext ( ESContext *esContext ) { if ( esContext != NULL ) { memset( esContext, 0, sizeof( ESContext) ); } } from what I understand macros, they just replace what is defined by the macro.. although i don't understand what it is the point in this case.
Thanks.
This kind of macro is used to change the calling convention that is used by the compiler:
#define ESUTIL_API // nothing, use the standard calling convention or
#define ESUTIL_API __fastcall // use the fastcall calling convention The call type calling convention has usually to be put in a function definition between the return type and the function identifier name.
In this case is just a placeholder, in case one would ever need to add any decorations to the function declaration, more specifically, stuff like __declspec(dllexport), calling conventions or inlining requirements.
In this case ESUTIL_API macro can be replaced by the calling convention specification.
There may be some other place (or condition) where that macro is defined differently - for example a -D option to a compiler, or another block of code that is triggered by some other #defines. In that case you have to define at least an empty macro so that you can safely use it in a declaration like that and if the macro happens to be re-defined to a non-empty value - it will be used as such.
