未解决的外部

我有一个未解决的外部符号错误，这让我发疯了。简而言之，我有一个用于SDL_Surfaces的包装类（"DgSurface"）和一个用于加载和存储DgSurfaces的类（"DgSurfaceList"）。尝试在我的项目中包含 DgSurfaceList 文件时会出现链接问题。以下是我的课程：

头文件 "DgSurface.h" 包含 DgSurface 类声明：

    #ifndef DGSURFACE_H
    #define DGSURFACE_H
    #include "SDL.h"
    #include <string>
    class DgSurface
    {
    public:
        //Constructor/destructor
        DgSurface(std::string N, SDL_Surface* I): image(I), name(N) {}
        DgSurface() {name = ""; image = NULL;}
        ~DgSurface();
        //Copy operations
        DgSurface(const DgSurface&);
        DgSurface& operator= (const DgSurface&);
        //Data members
        std::string name;       //The name of the image
        SDL_Surface* image;     //The image
    };
    #endif

cpp 文件 "DgSurface.cpp" 包含 DgSurface 定义：

#include "DgSurface.h"
#include "SDL.h"
//--------------------------------------------------------------------------------
//        Constructor
//--------------------------------------------------------------------------------
DgSurface::DgSurface(const DgSurface& other)
{
    //Copy name
    name = other.name;
    //Create new SDL_Surface 
    image = SDL_ConvertSurface(other.image, other.image->format, 0);
}

//--------------------------------------------------------------------------------
//        Destructor
//--------------------------------------------------------------------------------
DgSurface::~DgSurface()
{
    SDL_FreeSurface(image);
}

//--------------------------------------------------------------------------------
//        Assignment operator
//--------------------------------------------------------------------------------
DgSurface& DgSurface::operator= (const DgSurface& other)
{
    // if same object
    if ( this == &other )
        return *this;
    //Copy name
    name = other.name;
    //Create new SDL_Surface 
    image = SDL_ConvertSurface(other.image, other.image->format, 0);
    return *this;
}

这个类似乎工作正常，并且按预期执行（但是，一如既往，我对反馈:)持开放态度。

"DgSurfaceList.h" 包含 DgSurfaceList 类声明：

#ifndef DGSURFACELIST_H
#define DGSURFACELIST_H
#include "SDL.h"
#include <list>
#include <string>
#include "DgSurface.h"

class DgSurfaceList
{
    public:
        //Constructors/destructor
        DgSurfaceList() {}
        ~DgSurfaceList() {}
        //Functions
        bool AddImage(std::string location, std::string name);
        //Return Functions
        SDL_Surface* GetImage(std::string S) const;
    private:
        //Data members
        std::list<DgSurface> imlist;    //The list of DgSurfaces
        //Functions
        SDL_Surface* LoadImage( std::string filename );
};

#endif

最后"DgSurfaceList.cpp"包含DgSurfaceList定义：

#include "SDL.h"
#include "SDL_image.h"
#include <list>
#include <string>
#include "DgSurface.h"
#include "DgSurfaceList.h"

//--------------------------------------------------------------------------------
//      Load an image from file
//--------------------------------------------------------------------------------
SDL_Surface* DgSurfaceList::LoadImage( std::string filename )
{
    //Loads an image from file, returns SDL_surface*
    ...
}   //End:DgSurfaceList::LoadImage()

//--------------------------------------------------------------------------------
//      Add a DgSurface to the list
//--------------------------------------------------------------------------------
bool DgSurfaceList::AddImage(std::string location, std::string name) 
{
    //Load the image
    DgSurface temp(name,LoadImage(location));
    //If there was an error in loading the image
    if( temp.image == NULL )
        return false;
    //If everything loaded fine, place a copy into imlist
    imlist.push_back(temp);
    return true;
}   //End: DgSurfaceList::AddImage();

//--------------------------------------------------------------------------------
//      Searches imlist for an image, returns a pointer to a SDL_Surface
//--------------------------------------------------------------------------------
SDL_Surface* DgSurfaceList::GetImage(std::string S) const
{
    std::list<DgSurface>::const_iterator i;
    //Search imlist for DgSurface of the same name
    for (i = imlist.begin(); i != imlist.end(); i++)
    {
        if (S.compare((*i).name) == 0)
            return (*i).image;
    }
    //Return Null if name not found
    return NULL;
}   //End:DgSurfaceList::GetImage()

现在，如果我注释掉 cpp 文件中的 DgSurfaceList：：GetImage（） 定义，DgSurfaceList 似乎工作正常并且可以正确存储图像。更具体地说，仅当我在上述函数中包含 for 循环时，才会出现链接错误。会是什么？

其他信息：

错误：

unresolved external symbol __imp___CrtDbgReportW referenced in function "public: class 
DgSurface const & __thiscall std::_List_const_iterator<class std::_List_val<class 
DgSurface,class std::allocator<class DgSurface> > >::operator*(void)const "

编码环境：视觉C++快递2010