IImage和链接错误

//========================================================================
//TITLE:
// IImage和链接错误
//AUTHOR:
// norains
//DATE:
// Tuesday 14-August-2007
//Environment:
// EVC4.0 + Windows CE 5.0 Standard SDK
//========================================================================

IImage组件是在wince5.0新加入的,它可以调用公共接口来显示多种图片格式(jpg,png,gif,bmp),并且还可以扩展用以支持更多图片.但也许是因为新加入的原因,尚存在不少问题,其中编译的error link 2005就令人非常头痛.

首先让我们先来看看一个能够编译通过的最简单IImage的用法:

//////////////////////////////////////////////////////////////////////
//TempApp.cpp:Definestheentrypointfortheapplication.
//
//////////////////////////////////////////////////////////////////////

#include"stdafx.h"
#include"initguid.h"
#include"imaging.h"

#pragmacomment(lib,"Ole32.lib")

voidOpen()
{

IImage*pImage;
IImagingFactory*pImagingFactory;

HRESULThr;

if(FAILED(hr=CoInitializeEx(NULL,COINIT_MULTITHREADED)))
{
gotoEND;
}

if(FAILED(hr=CoCreateInstance(CLSID_ImagingFactory,NULL,CLSCTX_INPROC_SERVER,IID_IImagingFactory,(void**)&pImagingFactory)))
{
gotoEND;
}

if(FAILED(hr=pImagingFactory->CreateImageFromFile(TEXT("测试.bmp"),&pImage)))
{
gotoEND;
}


END:
if(pImage!=NULL)
{
pImage->Release();
pImage=NULL;
}

if(pImagingFactory!=NULL)
{
pImagingFactory->Release();
pImagingFactory=NULL;
}

CoUninitialize();

}



intWINAPIWinMain(HINSTANCEhInstance,
HINSTANCEhPrevInstance,
LPTSTRlpCmdLine,
intnCmdShow)
{
//TODO:Placecodehere.

Open();
return0;
}

在这个文件中,我们需要注意两点

1.头文件的包含次序.
#include "initguid.h"一定要在#include "imaging.h"之前.如果不包含"initguid.h"或在#include "imaging.h"之后含,则编译时会出现错误:
TempApp.obj : error LNK2001: unresolved external symbol CLSID_ImagingFactory
TempApp.obj : error LNK2001: unresolved external symbol IID_IImagingFactory

2."Ole32.lib"需要pragma
如果"Ole32.lib"没有pragma的话,那么编译的时候将会出现如下错误:
TempApp.obj : error LNK2019: unresolved external symbol __imp_CoUninitialize referenced in function "void __cdecl Open(void)" (?Open@@YAXXZ)
TempApp.obj : error LNK2019: unresolved external symbol __imp_CoCreateInstance referenced in function "void __cdecl Open(void)" (?Open@@YAXXZ)
TempApp.obj : error LNK2019: unresolved external symbol __imp_CoInitializeEx referenced in function "void __cdecl Open(void)" (?Open@@YAXXZ)
MIPSIIDbg/TempApp.exe : fatal error LNK1120: 3 unresolved externals




如果将IImage组件用类的形式封装,那么在头文件的包含顺序就更有讲究.

这个是一个完整的能通过编译的例子:

//////////////////////////////////////////////////////////////////////
//TempApp.cpp:Definestheentrypointfortheapplication.
//
//////////////////////////////////////////////////////////////////////

#include"stdafx.h"
#include"imgtest.h"




intWINAPIWinMain(HINSTANCEhInstance,
HINSTANCEhPrevInstance,
LPTSTRlpCmdLine,
intnCmdShow)
{
//TODO:Placecodehere.

CImgTestimgTest;
imgTest.Open();
return0;
}

//////////////////////////////////////////////////////////////////////
//ImgTest.h:interfacefortheCImgTestclass.
//
//////////////////////////////////////////////////////////////////////

#ifndefIMGTEST_H
#defineIMGTEST_H

#include"imaging.h"

classCImgTest
{
public:
voidOpen();
CImgTest();
virtual~CImgTest();

protected:
IImage*pImage;
IImagingFactory*pImagingFactory;
};

#endif//#ifndefIMGTEST_H

//////////////////////////////////////////////////////////////////////
//ImgTest.cpp:implementationoftheCImgTestclass.
//
//////////////////////////////////////////////////////////////////////

#include"stdafx.h"
#include"initguid.h"
#include"ImgTest.h"


#pragmacomment(lib,"Ole32.lib")


CImgTest::CImgTest()
{

}

CImgTest::~CImgTest()
{

}

voidCImgTest::Open()
{


HRESULThr;

if(FAILED(hr=CoInitializeEx(NULL,COINIT_MULTITHREADED)))
{
gotoEND;
}

if(FAILED(hr=CoCreateInstance(CLSID_ImagingFactory,NULL,CLSCTX_INPROC_SERVER,IID_IImagingFactory,(void**)&pImagingFactory)))
{
gotoEND;
}

if(FAILED(hr=pImagingFactory->CreateImageFromFile(TEXT("测试.bmp"),&pImage)))
{
gotoEND;
}


END:
if(pImage!=NULL)
{
pImage->Release();
pImage=NULL;
}

if(pImagingFactory!=NULL)
{
pImagingFactory->Release();
pImagingFactory=NULL;
}

CoUninitialize();
}

CImgTest是将IImage COM封装的一个类,在这里例子里我们尤为要注意的是#include "initguid.h"的位置:位于"ImgTest.cpp"中,并且在"ImgTest.h"之前.看到这里,可能有的朋友会觉得奇怪,直接将#include "initguid.h"写在"ImgTest.h"中不行么?答案是否定的.

我们可以更改头文件的包含,做个测试.

更改后的头文件如下:

//////////////////////////////////////////////////////////////////////
//ImgTest.h:interfacefortheCImgTestclass.
//
//////////////////////////////////////////////////////////////////////

#ifndefIMGTEST_H
#defineIMGTEST_H

#include"ImgTest.h"
#include"imaging.h"

classCImgTest
{
public:
voidOpen();
CImgTest();
virtual~CImgTest();

protected:
IImage*pImage;
IImagingFactory*pImagingFactory;
};

#endif//#ifndefIMGTEST_H

编译时将出现错误:
ImgTest.obj : error LNK2005: ENCODER_SAVE_FLAG already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_CHROMINANCE_TABLE already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_LUMINANCE_TABLE already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_TRANSFORMATION already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_ROTATION already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_QUALITY already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_RENDERMETHOD already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_VERSION already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_SCANMETHOD already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_COLORDEPTH already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ENCODER_COMPRESSION already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: DECODER_USEICC already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: DECODER_ICONRES already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: DECODER_OUTPUTCHANNEL already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: DECODER_TRANSRANGE already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: DECODER_TRANSCOLOR already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FMTID_JpegAppHeaders already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FMTID_ImageInformation already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FRAMEDIM_PAGE already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FRAMEDIM_RESOLUTION already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FRAMEDIM_TIME already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IImageBytes already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IBasicBitmapOps already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IImageSink already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IImageEncoder already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IImageDecoder already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IBitmapImage already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IImage already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: CLSID_ImagingFactory already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IID_IImagingFactory already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_ICO already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_FLASHPIX already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_PHOTOCD already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_EXIF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_TIFF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_GIF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_PNG already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_JPEG already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_WMF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_EMF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_BMP already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_MEMORYBMP already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: IMGFMT_UNDEFINED already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: CodecIImageBytes already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderSaveFlag already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderChrominanceTable already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderLuminanceTable already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderTransformation already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderQuality already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderRenderMethod already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderVersion already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderScanMethod already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderColorDepth already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: EncoderCompression already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FormatIDJpegAppHeaders already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FormatIDImageInformation already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FrameDimensionPage already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FrameDimensionResolution already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: FrameDimensionTime already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatIcon already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatEXIF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatTIFF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatGIF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatPNG already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatJPEG already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatWMF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatEMF already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatBMP already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatMemoryBMP already defined in ImageIntroduce.obj
ImgTest.obj : error LNK2005: ImageFormatUndefined already defined in ImageIntroduce.obj


那么在"ImgTest.cpp"中将#include "initguid.h"放置 #include "ImgTest.h"之后也不行么?答案依然是否定的.如果放在之后,则编译时会出现如下错误:
ImgTest.obj : error LNK2001: unresolved external symbol CLSID_ImagingFactory
ImgTest.obj : error LNK2001: unresolved external symbol IID_IImagingFactory
MIPSIIDbg/ImageIntroduce.exe : fatal error LNK1120: 2 unresolved externals


IImage的使用很简单也很方便,唯一需要注意的仅仅是#include "initguid.h"语句的位置而已,而这点却又往往让我们忽略,从而造就一些莫名其妙的链接错误.