These are used to direct the compiler to compile/or not compile the lines that follow
#ifdef NULL #define NL 10 #define SP 32 #endif
In the preceding case, the definition of NL and SP will only occur if NULL has been defined prior to the compiler encountering the #ifdef NULL statement. The scope of a definition may be limited by
This renders the identification of NULL invalid from that point onwards in the source file.
ęCopyright B Brown. 1984-1999. All rights reserved.