#include causes error

Question

When I include gdiplus.h in a program that compiles well the first(there are many) error I get is:

c:\program files (x86)\microsoft sdks\windows\v7.0a\include\GdiplusImaging.h(77): error C2504: 'IUnknown' : base class undefined

Part of GdiplusImaging.h:

IImageBytes : public IUnknown  <<< error!
{
public:
     ...

Why it is so? Where is this IUnknown class? And why it's not in GdiplusImaging.h?

My system is Windows7 x64. VisualStudio 2010.

Including part:

#include <windows.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib, "gdiplus.lib")

If reinstalling the sdk doesn't solve the problem, try setting "Show Includes" (under C/C++ -> advanced) to `Yes`, and recompile. You'll see the order of includes in the output window. Could make things clearer. — Eran, Sep 05 '11 at 08:53
thanks for the tip, simple including of Unknwn.h saved my soul — Sergey, Sep 05 '11 at 09:31

score 35 · Accepted Answer · answered Sep 05 '11 at 11:17

35

These are the standard includes for using GDI+:

#include <windows.h>
#include <objidl.h>
#include <gdiplus.h>
using namespace Gdiplus;
#pragma comment (lib,"Gdiplus.lib")

answered Sep 05 '11 at 11:17

SChepurin

I used this exact block, but still had issues with min/max macros being undefined in gdiplustype.h file (that is included internally by gdiplus.h). Following thread helped -http://stackoverflow.com/questions/4913922/possible-problems-with-nominmax-on-visual-c – Aditya Kumar Pandey Jun 15 '15 at 13:48
This doesn't work under VS2017 if you try to build it for platform toolset as `Visual Studio 2017 - Windows XP (v141_xp)`. Here's [more info](https://stackoverflow.com/questions/57014731/gdi-library-causes-error-c2760-syntax-error-unexpected-token-identifier-e). Did anyone figure out how to build these GDI+ libraries? – c00000fd Jul 13 '19 at 17:29

score 7 · Answer 2 · edited Jul 04 '21 at 03:53

7

You should try to add windows.h and Unknwn.h header before gdiplus.h

#include <Unknwn.h>
#include <windows.h>
#include <gdiplus.h>

edited Jul 04 '21 at 03:53

evandrix

answered Sep 05 '11 at 08:37

Cedekasme

Have you try to force adding the `Unknwn.h` header before calling `gdiplus.h` ? – Cedekasme Sep 05 '11 at 08:47
I wonder WHY not to include it in gdi headers?? It helped! thanks. Add it to the answer. – Sergey Sep 05 '11 at 09:29

2 Answers2