静态初始化 C++

Question

我对 C++ 的有限理解意味着我不知道如何正确执行以下操作：

#include "Platform.h"
#include "Global.h"

SDL_Surface *ms_pSmall (Global::sharedGlobal()->loadImage(RESOURCE_SMALL_PLATFORM) );
SDL_Surface *ms_pMedium(Global::sharedGlobal()->loadImage(RESOURCE_MEDIUM_PLATFORM));
SDL_Surface *ms_pLarge (Global::sharedGlobal()->loadImage(RESOURCE_LARGE_PLATFORM) );

//Initialise platform variables
Platform::Platform()
{   
    int imgSize = rand() % 3;
    switch (imgSize)
    {
        case 2:
            m_pImage = ms_pSmall;
            break;
        case 1:
            m_pImage = ms_pMedium;
            break;
        case 0:
            m_pImage = ms_pLarge;
            break;
    }
}

其中 ms_pSmall 等是静态指针，Global 是具有以下函数声明的单例：

static Global* sharedGlobal();
SDL_Surface* loadImage(const std::string& filename) const;

代码似乎编译正确，但链接器抱怨：

Undefined symbols for architecture i386:"Platform::ms_pMedium", referenced from:
  Platform::Platform() in Platform.o    "Platform::ms_pLarge", referenced from:
  Platform::Platform() in Platform.o    "Platform::ms_pSmall", referenced from:
  Platform::Platform() in Platform.o 
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

[抱歉缩进不佳。]

这里的任何帮助都将不胜感激，我会很乐意展示更多代码，但我认为这就是人们需要了解我正在尝试做什么的全部内容。

提前致谢！

Answer 1

您需要对成员进行限定：

SDL_Surface* Platform::ms_pSmall (Global::sharedGlobal()->loadImage(RESOURCE_SMALL_PLATFORM) );
SDL_Surface* Platform::ms_pMedium(Global::sharedGlobal()->loadImage(RESOURCE_MEDIUM_PLATFORM));
SDL_Surface* Platform::ms_pLarge (Global::sharedGlobal()->loadImage(RESOURCE_LARGE_PLATFORM) );

否则，您只是声明了其他变量，而函数中的静态变量未定义。