C1009: Invalid redeclaration

[ERROR]

Classes, structures and unions may be declared only once. Function redeclarations must have the same parameters and return values as the original declaration. In C++, data objects cannot be redeclared (except with the extern specifier).

  struct A {

  

    int i;

  

  };

  

  struct A { // error

  

    int i;

  

  };

  

Avoid redeclaration, e.g. guarding include files with ifndef.