Multi-platform library design. Best practices [closed]

Question

What are the best practices to design functions that have different platform-specific implementations?

For example, I have a function that structurally looks like this in a library module (it is exported):

void foo()
{
#ifdef PLATFORM_WINDOWS
  // windows-specific implementation
#elif PLATFORM_LINUX
  // linux-specific implementation
#elif PLATFORM_SOLARIS
  // solaris-specific implementation
#endif
}

Each section can (and does atm) contain a lot of code, which makes it difficult to read and so on.

What is the proper way to do things like this?

Answer 1

If the implementations are completely different, it may be a good idea to not use preprocessor conditions, but have separate .c files for each platform. Each would contain different, platform-specific implementations of the same functions declared in a shared header file. The correct file would then be selected by the build system.

For example in GLFW, there is x11_window.c and win32_window.c, and both implement the same functions, like _glfwPlatformGetWindowSize().