c中的重新定义错误

Question

I have to include "windows.h".The problem is redefinition, In windows.h:

_gdi_entry WINGDIAPI BOOL  WINAPI Polygon(__in HDC hdc, __in_ecount(cpt)
                                            CONST POINT *apt, __in int cpt);

Part of my code is(comes from other include):

typedef struct Polygon
{
    U8 numElements;
    PolygonPoints element[15];    
}Polygon;

I can't change the definition in my code. I am including windows.h for ShellExecute(). Tried to undef:

#ifdef Polygon 
#undef Polygon
#endif

Didn't help..

EDIT: Solved the problem with rodrigo's answer.

Answer 1

The #undef Polygon won't work because Polygon() is a real function, not a macro. In Windows, that trick mostly works for functions that takes at least one string argument, because of the Unicode vs ANSI stuff.

If you only want the ShellExecute() function you can omit all the GDI functions by defining NOGDI before including Windows.h :

#define NOGDI
#include <windows.h>

Alternatively you can add the NOGDI macro to the preprocessor project options of your IDE.

Answer 2

Separate the inclusion of windows.h and the definition of struct Polygon into two different files.

The file that includes windows.h will define a function that takes string parameters (and other non-struct Polygon parameter) and calls ShellExecute . The function is exported.

The file that defines struct Polygon must not include windows.h, but can convert the struct data to a string format and call the exported function defined in the other file.

Answer 3

Say hello to namespace collision. First things first, the best way to completely avoid this kind of problem is to prefix all your own identifiers with something unambiguous. For example if your project is called "foobar turboencabulator" a viable prefix would be fbtec… . You should do that unconditionally, because you'll never know which identifiers the OS and/or runtime environment may introduce in the future. The C language standard provisions a few namespaces (reserved prefixes for identifiers) for future expansion, but that's for C and not OSs and runtimes.

You were already given answers how to split up compilation units. But there's another possibility in your case and I strongly suggest you consider it. Your struct/typedef definition is

typedef struct Polygon
{
    U8 numElements;
    PolygonPoints element[15];    
}Polygon;

You tagged your question C so I suggest you embrace that fact: I suggest you drop the typedef . If you wrote just

struct Polygon
{
    U8 numElements;
    PolygonPoints element[15];    
};

without the typedef, then Polygon will exist in only the struct tag namespace, which is a different namespace than the one function identifiers reside in. So it will no longer collide with the Polygon function of Windows.

The downside to this is, that you'll have to change all variable and parameter definitions to refer to the struct namespace, ie Polygon a becomes struct Polygon a . OTOH it's idiomatic in C to be explicit about the struct namespace.