#ifdef Compile a section of code if an identifier is defined ------------------------------------------------------------------------------ Syntax #ifdef <identifier> <statements>... [#else] <statements>... #endif Arguments <identifier> is the name of a definition whose existence is being verified. Description #ifdef...#endif lets you perform a conditional compilation. It does this by identifying a section of source code to be compiled if the specified <identifier> is defined. The <identifier> can be defined using either the #define directive or the /D compiler option which lets you define an identifier or manifest constant from the compiler command line. The #else directive specifies the code to compile if <identifier> is undefined. The #endif terminates the conditional compilation block. Conditional compilation is particularly useful when maintaining many different versions of the same program. For example, the demo code and full system code could be included in the same program file and controlled by a single #define statement. Examples . This code fragment is a general skeleton for conditional compilation with #ifdef: #define DEMO . . <statements> . #ifdef DEMO <demo specific statements> #endif . This example controls conditional compilation with an identifier defined on the compiler command line with the /D option. In DOS: C>CLIPPER Myfile /DDEBUG In the program (.prg) file: #ifdef DEBUG Assert(<some condition>) #endif . This example defines a manifest constant to one value if it does not exist and redefines it to another if it exists: #ifdef M_MARGIN #undef M_MARGIN #define M_MARGIN 15 #else #define M_MARGIN 10 #endif
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