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C - Conditional Compilation2

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Conditional Compilation ...

  • e.g, 1

To make sure that the contents of file hdr.h are included only once, the contents of the file are surrounded with a condition like this

#if  !defined(HDR)
#define   HDR
// contents of hdr.h go here
#endif
  • e.g, 2
#ifdef identifier   is equ  #if defined    identifier
#ifndef             is equ  #if !defined identifier