C++ cross platform code

Unfortunately, non of our developers ever wrote any code in any other platform than Windows! Therefore, I have to give them a "code like this" or "not code like this" list, so the code will stay cross platform.

any guidance?

One way of increasing portability is to use the same compiler, GCC, on both platforms. If you also use the same compiler version, you will probably avoid most, if not all C++ language and Standard Library incompatibilities. You can also use the same build tools, such as GNU make, which means the build process is the same on both platforms.

As for platform incompatibilities - check that their code does not contain includes like:

#include <windows.h>
#include <unistd.h>
#include <sys/almost_anything.h>

unless this is done via conditional compilation.

Make sure that you have automated build processes on all platforms, and write unit and automated functional tests. If possible run automated nightly builds and tests. It's much more important when you are writing cross platform libraries.

I would do the opposite of one of the other answers (Not that i think it's wrong, just a different approach) and if you can choose your platforms make them as different as possible. For example make one 32 bit MCVC and the other 64 bit gcc on unix. If you can have automated tests and builds then this will show up portability issues quickly.

If possible have some developers working on one platform and some on another rather than finishing the code on one platform and then "porting" it to the other. That way they'll learn very quickly what not to do when their co workers come over to complain they broke something.

Technically things to watch out for are