Question

I’ve got a very large application built using Visual Studio 2008 which is designed to run on Windows XP. The code consists of one solution file which contains six separate projects. My job is to port this application to run on Linux. I have not done anything like this before.

I discovered yesterday that my company wishes for this code to still compile on Windows once I’m done with it. My first idea for accomplishing this is to use a preprocessor statement such as:

#define COMPILE_FOR_LINUX

Then, I could tell the compiler which files to include in the headers using preprocessor blocks like these:

#ifdef COMPILE_FOR_LINUX
// include required Linux headers here and skip Windows header includes
#else
// include required Windows headers here and skip Linux header includes
#endif

After including the appropriate files, I could encapsulate all the platform dependent code with blocks like these:

#ifdef COMPILE_FOR_LINUX
// compile Linux specific code used here.
#else
// compile Windows specific code used here.
#endif

In order to make it as easy as possible for somebody to compile the application for their preferred platform, I’d like to have COMPILE_FOR_LINUX specified in just one place. However, I’m not sure how to accomplish this.

One idea I had was to create an empty header file, and then have every single file in the solution include this header file as specified in the Visual Studio solution file include path. For Linux, I’d have another version of the header file which defines COMPILE_FOR_LINUX, and then have the makefile point to this version instead of the empty one. However, I’m sure this is a very crude solution, and I’m unsure if it will even work.

Could anybody suggest a more elegant method for defining something globally or creating a variable in such a way that every file in the solution can see it?

Answer 1

It depends on the compiler you’re using, but for gcc you can specify preprocessor directives from the command line, so you’ll just need to add COMPILE_FOR_LINUX in your makefile.

g++ -DCOMPILE_FOR_LINUX .....

For windows, if using MSVS, you can change the Preprocessor directives tab in the project properties (actually, you don’t need to, since COMPILE_FOR_LINUX isn’t defined, but you can add a COMPILE_FOR_WINDOWS for consistency).