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Tip of the Day
Home » Tip Bank » C++
Language: C++
Expertise: Beginner
Apr 24, 2000

WEBINAR:

On-Demand

Application Security Testing: An Integral Part of DevOps


Undoing a Macro

If you happen to define an object or a function or a constant whose name collides with a macro located elsewhere in a third-party header file, as in:

 
  // file defs.h 
  //...many declaration
  #define PI 3.14

  // your program:
  #include "defs.h"
  const double PI = 3.14159265358; // error, 'PI' redefined

you can use the #undef preprocessor directive to cancel a previously-defined macro:

 
  #include "defs.h"
  #undef PI  // from now on, ignore the PI macro
  const double PI = 3.14159265358979 // OK
Danny Kalev
 
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