无法从'SDL_Surface'转换为'SDL_Surface MainMenu::*'

情况：我试图在MainMenu类中有一个load_image方法，这样在我的主类中，我可以在主菜单中调用load_image方法。

问题：在load_image方法中，我得到错误：

错误C2440:"return"：无法从"SDL_Surface"转换为'SDL_Surface主菜单：：*'

这发生在第47行，红色下划线为"optimizedImage"。

这是头文件：

#ifndef MAINMENU_H
#define MAINMENU_H
#include <iostream>
#include <string>
#include "SDL.h"
#include "SDL_image.h"
using namespace std;
class MainMenu
{
    private:
        string menuOption[3];
        string background;
        string img1;
        string img2;
        string img3;
        SDL_Surface *screen;
        SDL_Surface *bkgrnd;
        SDL_Surface *item;
public:
    MainMenu(SDL_Surface *screen, string bgImg, string optionImg1, string optionImg2, string optionImg3) 
        : background(bgImg), img1(optionImg1), img2(optionImg2), img3(optionImg3)
    {
    }
    ~MainMenu();
    SDL_Surface  *load_image(string filename);
    void apply_surface(int x, int y, SDL_Surface* source, SDL_Surface* destination);
    bool load_files();
    void Draw();
};
#endif

这是.cpp文件：

#include <iostream>
#include <string>
#include "MainMenu.h"
#include "glut.h"
#include "SDL.h"
#include "SDL_image.h"
MainMenu::~MainMenu()
{
}

SDL_Surface  MainMenu::*load_image(string filename)
{
//Temporary storage for the image tgat loaded
    SDL_Surface* loadedImage = NULL;
    //The optimized image that will be used
    SDL_Surface* optimizedImage = NULL;
    //Load the image
    loadedImage = IMG_Load(filename.c_str());
    //If nothing went wrong in loading the image
    if (loadedImage != NULL)
    {
        //Create an optimized image
        optimizedImage = SDL_DisplayFormat(loadedImage);
        //Free the old image
        SDL_FreeSurface(loadedImage);
        //if the image was optimized just fine
        if (optimizedImage != NULL)
        {
            //Map the color key
            Uint32 colorkey = SDL_MapRGB( optimizedImage->format,0,0xFF,0xFF);
            //Set all pixels of color R 0, G 0xFF, B 0xFF to be transparent
            SDL_SetColorKey(optimizedImage, SDL_SRCCOLORKEY, colorkey);
        }
        return optimizedImage;
    }
    return optimizedImage;
}
void MainMenu::apply_surface(int x, int y, SDL_Surface* source, SDL_Surface* destination)
{
    SDL_Rect offset;
    //Give the offsets to the rectangle
    offset.x = x;
    offset.y = y;
    SDL_BlitSurface(source, NULL, destination, &offset);
}
bool MainMenu::load_files()
{
    //Load images
    item = load_image(img1);
    bkgrnd = load_image(background);
    if (item == NULL || bkgrnd == NULL)
    {
        return false;
    }
    return true;
}
void MainMenu::Draw()
{
    apply_surface(0, 0, bkgrnd, screen);
    apply_surface(320, 0, bkgrnd, screen ); 
    apply_surface(0, 240, bkgrnd, screen ); 
    apply_surface(320, 240, bkgrnd, screen );
    apply_surface(180, 140, item, screen ); 
}