Conditional compiling Foundation

One fundamental strength of the preprocessor is the ability to compile source code differently depending on defined symbolic constants and their values. Based on whether or not a constant is defined, different parts of a source code file are compiled using #ifdef or #ifndef. To compare values the more complex #if can be used.

This is a sample how to use #ifdef.

#define GERMAN_LANGUAGE 

PROCEDURE Main() 

  #ifdef GERMAN_LANGUAGE 
     ? "Das ist die deutsche Version" 
  #else 
     ? "This is the English version" 
  #endif 

RETURN 

Conditional compilation is done using the directives #ifdef, #ifndef, #else and #endif, which provide branching for the preprocessor. When the directives #ifdef and #ifndef are used, the preprocessor tests whether a symbolic constant is defined. Depending on the existence of the #define constant, the preprocessor translates various parts of the source code. In the example, the program can be compiled in two different language versions based on whether the GERMAN_LANGUAGE constant is defined. The section of the source code that is not appropriate is removed and does not exist in the preprocessed code received by the compiler.

This is a sample how to use #if. The .prg file is compiled by calling xpp /dTARGET_VER=0 test.prg.

#define VERSION_MIN 1 

PROCEDURE Main() 

  #if TARGET_VER < VERSION_MIN 
     ? "You need to upgrade to version" + str(VERSION_MIN) 
  #endif 

RETURN