小编Fra*_*ank的帖子

我有一个未解决的外部符号错误,这让我疯狂.简而言之,我有一个SDL_Surfaces包装类('DgSurface')和一个加载和存储DgSurfaces('DgSurfaceList')的类.尝试在我的项目中包含DgSurfaceList文件时出现链接问题.这是我的课程:

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);
} …

我可以按如下方式验证函数签名：

template <typename>
struct FnType
{
  static bool const valid = false;
};

struct FnType<void(int)>
{
  static bool const valid = true;
};

void foo(int)
{

}

FnType<decltype(foo)>::valid; //true

如何验证类方法签名？

class Y
{
public:
  void foo(int)
  {

  }
};

FnType<decltype(&Y::foo)>::valid; //false?? 

我想验证Y::foo返回类型和参数类型是否有效。