C++ DLL linker error - c++

Question

I want to write a dll for an api of a device. since i am new to dlls i wanted to implement it on a simple text editor and then make one for the api.
I have made header file and cpp file but when i run the code i get error lnk2001 followed by lnk1120 which is unresolved external error.
I really have no idea where did i make a mistake, as far as i see i did it the right way. i was wondering if you guys could help me out. tnx.
here is my header file
// EditFuncsDll.h
#include <cstdio>
#include <vector>
#include <string>
namespace EditFuncs
{
class MyEditFuncs
{
private:
static std::vector<std::string> MyTextBox;
public:
static __declspec(dllexport) void Load(std::string command);
static __declspec(dllexport) void Save(std::string command);
static __declspec(dllexport) int Lines();
static __declspec(dllexport) void Add(std::string command);
static __declspec(dllexport) void Remove(std::string command);
static __declspec(dllexport) void Insert(std::string command);
static __declspec(dllexport) int wc(std::string command);
static __declspec(dllexport) void GetInfo();
};
}
and in my cpp file i just define the functions i declared in header file.
and these are the errors i get
Error 25 error LNK2001: unresolved external symbol "private: static class std::vector,class std::allocator >,class std::allocator,class std::allocator > > > EditFuncs::MyEditFuncs::MyTextBox" (?MyTextBox#MyEditFuncs#EditFuncs##0V?$vector#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std##V?$allocator#V?$basic_string#DU?$char_traits#D#std##V?$allocator#D#2##std###2##std##A) C:\Users\Lucy\Desktop\Erfan\Text_Editor_DLL\Text_Editor_DLL\EditFuncsDll.obj Text_Editor_DLL
and
Error 26 error LNK1120: 1 unresolved externals C:\Users\Lucy\Desktop\Erfan\Text_Editor_DLL\Debug\Text_Editor_DLL.dll Text_Editor_DLL

Answer 1

The head of your cpp should be like this :
#include "EditFuncsDll.h"
#include <iostream>
#include <fstream>
using namespace std;
namespace EditFuncs
{
std::vector<std::string> EditFuncs::MyEditFuncs::MyTextBox;
void MyEditFuncs::Load(string command)
{
string filename; // The name of the file starts at the fifth character of the command and goes to the end
filename = command.substr(5,command.size());
ifstream inFile;
inFile.open(filename);
.
.
.

Answer 2

In your DLL's header file you may want to use a preprocessor macro, that expands to __declspec(dllimport) for DLL clients, and to __declspec(dllexport) for code that is implementing the DLL (i.e. your DLL .cpp files).
// EditFuncsDll.h
#ifdef EDIT_FUNCS_DLL_IMPLEMENTATION
#define EDIT_FUNCS_DLL __declspec(dllexport) // for DLL implementation
#else
#define EDIT_FUNCS_DLL __declspec(dllimport) // for clients
#endif
class EDIT_FUNCS_DLL MyEditFuncs
{
...
};
In your DLL's source .cpp file(s), you can #define EDIT_FUNCS_DLL_IMPLEMENTATION before #including your DLL header:
// EditFuncsDll.cpp
#define EDIT_FUNCS_DLL_IMPLEMENTATION
#include "EditFuncsDll.h"
// ... implementation code