Compiler Error C2009

The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.

The latest version of this topic can be found at Compiler Error C2009.

reuse of macro formal 'identifier'

The formal parameter list of a macro definition uses the identifier more than once. Identifiers in the macro's parameter list must be unique.

The following sample generates C2009:

// C2009.cpp  
#include <stdio.h>  
  
#define macro1(a,a) (a*a)   // C2009  
  
int main()   
{  
    printf_s("%d\n", macro1(2));  
}  

Possible resolution:

// C2009b.cpp  
#include <stdio.h>  
  
#define macro2(a)   (a*a)   
#define macro3(a,b) (a*b)  
  
int main()   
{  
    printf_s("%d\n", macro2(2));  
    printf_s("%d\n", macro3(2,4));  
}