错误LNK2001:无法解析的外部符号public:静态类 [英] error LNK2001: unresolved external symbol public: static class

问题描述

我无法弄清楚为什么收到此错误.任何人都可以伸出援手. 我需要在头文件中声明VideoCapture Capture，并在Video.cpp中调用它

I cannot figure out why i am recieving this error. Can anyone lend a hand. I need to declare VideoCapture capture in the header file and call it in Video.cpp

Video.h

class Video
{
    public:

    static VideoCapture capture;

    //Default constructor
    Video();

    //Declare a virtual destructor:
    virtual ~Video();

    //Method
    void Start();   

    private:
};

Video.cpp

#include "StdAfx.h"
#include "Video.h"
#include "UserInfo.h"
#include "Common.h"

void Video::Start()
{
  while(1)
  {
    Mat img;

    bool bSuccess = capture.read(img); // read a new frame from video

     if (!bSuccess) //if not success, break loop
    {
                    cout << "End of video" << endl;
                   break;
    }

    imshow("original video", img); //show the frame in "Original Video" window

    if(waitKey(30) == 27) //wait for 'esc' key press for 30 ms. If 'esc' key is pressed, break loop
   {
            cout << "esc key is pressed by user" << endl; 
            break; 
   }
  }
}

任何帮助将不胜感激

推荐答案

在类定义中，static变量仅是声明.您只声明了capture将在某处存在.

In a class definition, static variables are a merely a declaration. You have only declared that capture will exist somewhere.

您需要添加定义.使变量存在.

You need to add the definition. Make the variable exist.

在任何版本的C ++中

您可以在cpp文件中单独定义变量.

You can separately define the variable in your cpp file.

const VideoCapture Video::capture;

在C ++ 17或更高版本中

您可以在标头中声明变量inline以使其成为定义.

You can declare the variable inline in your header to make it a definition.

static inline VideoCapture capture;

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