8.7 Writing codes fragments which are specific to DJGPP

Q: I must put a DJGPP-specific code fragment into my program. What symbol should I use in the #ifdef directive to make it only visible under DJGPP?

A: Use __DJGPP__, like this:

    #ifdef __DJGPP__
    ... DJGPP-specific code ...
    #else
    ... not seen under DJGPP ...
    #endif

__DJGPP__ has the value of the DJGPP major revision number, so you can write code fragments which have different behavior under different versions of DJGPP:

    #ifdef __DJGPP__
    #if __DJGPP__ > 2
    .... will work only in DJGPP v3.x and later ...
    #else
    .... get here for DJGPP v2.x ...
    #endif
    #else
    .... get here in DJGPP v1.x or non-DJGPP environment
    #endif

If you need to distinguish between minor DJGPP revision numbers, use the symbol __DJGPP_MINOR__. For example:

    #if defined(__DJGPP__) && __DJGPP__ == 2 && __DJGPP_MINOR__ == 1
    .... will work only in DJGPP v2.01 ....
    #endif

Another DJGPP-specific pre-processor symbol which DJGPP defines is __GO32__; but it is only provided for compatibility with previous versions of DJGPP (v1.x) and its use should be discouraged.