Compiler Warning (level 4) C4668

 

For the latest documentation on Visual Studio 2017, see Visual Studio 2017 Documentation.

For the latest documentation on Visual Studio 2017, see Compiler Warning (level 4) C4668 on docs.microsoft.com. 'symbol' is not defined as a preprocessor macro, replacing with '0' for 'directives'

A symbol that was not defined was used with a preprocessor directive. The symbol will evaluate to false. To define a symbol, you can use either the #define directive or /D compiler option.

This warning is off by default. See Compiler Warnings That Are Off by Default for more information.

The following sample generates C4668:

// C4668.cpp  
// compile with: /W4  
#include <stdio.h>  
  
#pragma warning (default : 4668)   // turn warning on  
  
int main()   
{  
    #if q   // C4668, q is not defined  
        printf_s("defined");  
    #else  
        printf_s("undefined");  
    #endif  
}  

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