C++ LANGUAGE #DEFINE PREPROCESSOR

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C++ LANGUAGE #DEFINE PREPROCESSOR

The #define Preprocessor 


The #define preprocessor directive creates symbolic 
constants. The symbolic constant is called a macro and 
the general form of the directive is: 

#define macro-name replacement-text  

When this line appears in a file, all subsequent occurrences 
of macro in that file will be replaced by replacement-text 
before the program is compiled. For example: 

#include <iostream> 
using namespace std; 
 
#define PI 3.14159 
 
int main () 
{ 
  
    cout << "Value of PI :" << PI << endl;  
 
    return 0; 
} 
35. PREPROCESSOR 
test.p. Now, if you check test.p, it will have lots of information 
and at the bottom, you will find the value replaced as follows: 

$gcc -E test.cpp > test.p 
 
... 
int main () 
{ 
  
    cout << "Value of PI :" << 3.14159 << endl;  
 
    return 0; 
}