如何解决错误LNK2019：无法解析的外部符号

Question

这样一个非常小的程序让我疯狂。我总是得到以下错误消息：

Error 1 error LNK2019: unresolved external symbol "public: class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __thiscall ErstesPraktikum::createNameString(class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> >,int)" (?createNameString@ErstesPraktikum@@QAE?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@V23@00H@Z) referenced in function _main Praktikum_gra.obj GRA 
Error 2 fatal error LNK1120: 1 unresolved externals C:\Users\xxx\Documents\Visual Studio 2008\Projects\GRA\Debug\GRA.exe GRA 

这里是我的计划，该计划包含的类ErstesPraktikum和 Praktikum_gra加上相应的头文件。

我只是想用 Praktikum_gra类调用ErstesPraktikum类的方法。我花了几个小时解决这个错误，但没有成功。这是一个编程错误还是配置问题？我最后的希望是，你有人可以给我一个提示...

注：字符串是只是一个包装为的std :: OpenCV中的字符串。

ErstesPraktikum.h

#include <opencv2\core\core.hpp> 

using namespace std; 
using namespace cv; 

class ErstesPraktikum 
{ 
    private: 
     String convertInteger(int); 

    public: 
     String createNameString(String, String, String, int); 
     void readImage(String, Mat *); 
     void extractObjects(int, Mat *, Mat *); 
}; 

ErstesPraktikum.cpp

#include <opencv2\core\core.hpp> 
#include <opencv2\highgui\highgui.hpp> 
#include <opencv2\imgproc\imgproc.hpp> 
#include <fstream> 

using namespace std; 
using namespace cv; 


String convertInteger(int value) 
{ 
    stringstream ss; 
    ss << value; 
    return ss.str(); 
} 

String createNameString(String path, String fileName, String fileExtension, int buildNumber) 
{ 
    String pathString = path.append(fileName); 
    pathString = pathString.append("."); 
    pathString = pathString.append(convertInteger(buildNumber)); 
    pathString = pathString.append("."); 
    pathString = pathString.append(fileExtension); 

    return pathString; 
} 

void readImage(String nameString, Mat * image) 
{ 
    double mn = 0, mx = 0; 
    image = &cv::Mat(cv::Size(512, 512), IPL_DEPTH_8U, 1); 
    unsigned short *data; 
    data = (unsigned short *)image->data; 
    FILE *file; 
    file = fopen(nameString.c_str(), "rb"); 

    fseek(file, 1340, SEEK_SET); 
    fread(data, sizeof(unsigned short)*512*512, 1, file); 
    fclose(file); 


    //cv::cvSmooth(Image,Image); 

    //cv::minMaxLoc(image, &mn, &mx, NULL, NULL, 0); 
    //cv::convertScaleAbs(image, *target, 255/mx, -mn*255/mx); 
} 

void extractObjects(int threshold, Mat * img, Mat * binImg) 
{ 

} 

Praktikum_gra.h

class Praktikum_gra 
{ 
    public: 
     int main(void); 
} 

Praktikum_gra.cpp

#include "ErstesPraktikum.h" 

using namespace std; 
using namespace cv; 

    int main(void) 
    { 
     String path("C:\\Users\\xxx\\xxx\\xxx\\GRA P1\\Head_M\\"); 
     String fileName("vhm"); 
     String fileExtension("dcm"); 
     ErstesPraktikum prak; 

     for(int i = 1001; i <= 1245; i++) 
     { 
      String nameString = prak.createNameString(path, fileName, fileExtension, i); // this line is the cause of the error message, but why ? 
     } 

     return 0; 
    } 

我已经尝试过的一类添加前缀像所有的方法：

String ErstesPraktikum::createNameString(String path, String fileName, String fileExtension, int buildNumber) 
{ 
    // [...] 
} 

但是，这将引发另一条错误消息：

Error 1 error C2653: 'ErstesPraktikum' : is not a class or namespace name c:\users\xxx\documents\visual studio 2008\projects\gra\gra_u1\erstespraktikum.cpp 17 GRA 

Answer 1

你必须

#include "ErstesPraktikum.h" 

in ErstesPrakticum.cpp。 然后，您需要在实现中使用ErstesPrakticum::。

String ErstesPraktikum::createNameString(....) { .... } 

等等。