std :: map是否需要初始化？

Question

I have a singleton, that is an image manager. When I try to load an image, I call singleton in this way:

utils::CImageBuff* img4 = utils::CImageManager::getInstance()->loadFromFile("uswg.png");

And, into loadFromFile method, I store the image into a map:

m_imageMap[imageHashID].setHeight(ilGetInteger(IL_IMAGE_HEIGHT));
m_imageMap[imageHashID].setWitdh(ilGetInteger(IL_IMAGE_WIDTH));
m_imageMap[imageHashID].setBpp(ilGetInteger(IL_IMAGE_BPP));
....

The problem is that I get a mem access error. Is like if m_imageMap is NULL o wrong initialized, because excepttion is thrown in the first sentence. But as I said, is a singleton so the map must me initialized. I'm developing in VC++ 2008. It could be a wrong compilation/ .obj file?

This was working well yesterday

Some advice?

Edit: The declaration of m_imageMap is very simple:

typedef std::map<unsigned int,utils::CImageBuff> t_imageMap;

As additional information, the exception generated is into the line 1643 of the file output.c.

Edit Well, I'm very dissapointed with this case. I've changed the code so now the class no longer is a singleton. Now only m_imageMap is static to make all loaded images visible from any place. But still fails in the same way. The error is an access violation . Moreover, if I change all the method code by this code by this:

utils::CImageBuff im;
m_imageMap[1] = im;    // fails here
return &im; 

still fails. It is like the map is null or locked in any way, or even bad initialized, but I don't know. Could you helpme?

If you need some more code, I'll paste, but crashing with this three lines simplifies the problem, I think.

Edit: Finally solved Finally I've changed from

std::map<unsigned int,utils::CImageBuff>

to

std::map<unsigned int,utils::CImageBuff*>

And now it works. Now I simply need to think a method to delete the contents of an static std::map of pointers.

Many thanks to all

Answer 1

I'm assuming that m_imageMap is a regular member variable of a class and you are calling this from a member function of that class.

If that is the case, then you are likely calling that member function on a zombie, null otherwise invalid pointer. Is the line of code with m_imageMap in it the first use of a member variable in that function? That's a pretty common giveaway.

The easy way to debug this problem is to look at it in the debugger. As long as this error happens in a debug build, VC++ will happily catch the access violation exception and break right there at that instant. Look at the value of the "this" pointer in the local variables watch window. Is it null or 0xcdcdcdcd ?

Answer 2

std::map does not require initialization- other than that provided by the appropriate constructor. As long as you called a constructor (the default one is fine too), then the map is properly initialized. The Singleton is a truly terrible pattern with many, many horrific problems, and you should excise such demons from your code, but none of them normally include this. You will need to post another question with the Singleton code in it to get help with the actual problem at hand.