Figure out function parameter count at compile time

Question

I have a C library (with C headers) which exists in two different versions.

One of them has a function that looks like this:

int test(char * a, char * b, char * c, bool d, int e); 

And the other version looks like this:

int test(char * a, char * b, char * c, bool d) 

(for which e is not given as function parameter but it's hard-coded in the function itself).

The library or its headers do not define / include any way to check for the library version so I can't just use an #if or #ifdef to check for a version number.

Is there any way I can write a C program that can be compiled with both versions of this library, depending on which one is installed when the program is compiled? That way contributors that want to compile my program are free to use either version of the library and the tool would be able to be compiled with either.

So, to clarify, I'm looking for something like this (or similar):

#if HAS_ARGUMENT_COUNT(test, 5)     test("a", "b", "c", true, 20); #elif HAS_ARGUMENT_COUNT(test, 4)     test("a", "b", "c", true); #else     #error "wrong argument count" #endif 

Is there any way to do that in C? I was unable to figure out a way.

The library would be libogc ( https://github.com/devkitPro/libogc ) which changed its definition of if_config a while ago, and I'd like to make my program work with both the old and the new version. I was unable to find any version identifier in the library. At the moment I'm using a modified version of GCC 8.3.

Answer 1

This should be done at the configure stage, using an Autoconf (or CMake, or whatever) test step -- basically, attempting to compile a small program which uses the five-parameter signature, and seeing if it compiles successfully -- to determine which version of the library is in use. That can be used to set a preprocessor macro which you can use in an #if block in your code.