VisualStudio 2012-两个项目->链接器错误（C ++）

Question

first my simple setup: I've got 2 VS2012 projects. Now I want to use classes from Project B in Project A. I added Project B to A's project dependencie list and imported the headers where necessary. (eg #include"..\\src-pool\\Coords.h";).

So far, so good - no compiler errors. But when I try to build the project, I get some linker errors:

Fehler  1   error LNK2019: Verweis auf nicht aufgelöstes externes Symbol ""public: __thiscall Coords::Coords(double,double)" (??0Coords@@QAE@NN@Z)" in Funktion ""public: void __thiscall TileDownloader::calculateBounds(double *,int)const " (?calculateBounds@TileDownloader@@QBEXPANH@Z)".  C:\Users\username\documents\visual studio 2012\Projects\CPPHA\project\TileDownloader.obj    

I'm sorry, this is the german version of VS. "Verweis auf nicht aufgelöstes externes Symbol" means: Link to not resolved extern symbol.

Any ideas? =)

---

Done this (this is a class I want to export and use in the other project)

Coords.h

#pragma once
#include <iostream>
#ifdef EXPORT_MYCLASS
#define MYCLASSEXPORT __declspec(dllexport)
#else
#define MYCLASSEXPORT __declspec(dllimport)
#endif


class  MYCLASSEXPORT  Coords
{
public:
    Coords(double lat, double lon);
    ~Coords(void);
    double getLon() const;
    void setLon(double val);
    double getLat() const;
    void setLat(double val);

    void printInfos() const;

private:
    double lat, lon;

};

But I get a warning "inconsistent dll export" and the same errors. Sorry, I'm new to C++

---

and I want to use it like this

#include "..\src-pool\Coords.h"

class TileDownloader
{
public:
    TileDownloader(void);
    ~TileDownloader(void);


    void  calculateBounds(double* array, int zoomLevel) const;
    void  downloadTiles() const;

private:
    double maxLat, maxLon, minLat, minLon;

};

Answer 1

There are 3 things that need to happen for the linker to find the a class method:

1. You reference the right dll/project
2. You have an implementation of that method in that dll/project.
3. It's exposed externally with a dll export ( __declspec(dllexport) )

Common practice for declaring an export in a header:

#ifdef EXPORT_MYCLASS
#define MYCLASSEXPORT __declspec(dllexport)
#else
#define MYCLASSEXPORT __declspec(dllimport)
#endif

class MyClass
{
     MYCLASSEXPORT MyClass();
}

Then you can just define that preprocessor argument in the exporting dll's preprocessor definitions.

In Visual studio:
Project properties -> Configuration properties -> C/C++ -> Preprocessor -> Prerpocessor deffinitios