LNK2001: unresolved external symbol VCPP 6.0: unresolved external symbol

LNK2001: unresolved external symbol VCPP 6.0

I have a .cpp file that I found online which calls a CreateThread instance as follows given under the code section as original.cpp

The program runs fine when I compile it as a W32-console application.

I am however trying to change it to a class so I can make use of this functionality in a different program that I want to write.

In my classname.h file, when I comment this function (remove it from the class), I get a list of LNK2001: unresolved external symbol errors.

If I keep it as a member of that class, however, I get the following message everytime I try to call the CreateThread

------------------------------------------------------------------------------
error C2664: 'CreateThread' : cannot convert parameter 3 from 'unsigned long (void *)' to 'unsigned long (__stdcall *)(void *)'
None of the functions with this name in scope match the target type
------------------------------------------------------------------------------

Can somebody please tell me what I'm missing out on???

Thank you

------------------------Original.cpp file---------------------------
DWORD WINAPI Func(LPVOID lpParameter){
...
}
 
int main (...) {
...
SOCKET *sock;
DWORD *dw;
CreateThread(NULL, 0, Func, sock, 0, &dw);
...
}

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------------class.h--------------- class classname { ... public: DWORD WINAPI function(LPVOID lParameter); }; ---------------class.cpp-------------------- DWORD WINAPI function(LPVOID lParameter) { ... ... } void classname::callingFunction() { ... ... SOCKET *sock; DWORD id; CreateThread(NULL, 0, function, sock, 0, &id); ... }

------------class.h--------------- class classname { ... public: DWORD WINAPI calledfunction(LPVOID lParameter); void callingFunction(); ... }; ---------------class.cpp-------------------- DWORD WINAPI classname::calledfunction(LPVOID lParameter) { ... ... } void classname::callingFunction() { ... ... SOCKET *sock; DWORD id; CreateThread(NULL, 0, calledfunction, sock, 0, &id); ... }

If you need a visual, here are your choices. Notice that I also pass "this" to the ThreadProc in callingfunction. This is because function cannot be a non-static method, so it is usually necessary to pass in an instance of the context object. The ThreadProc, "function" in this case, can be nothing more than a cast of the lpParameter to the correct type, classbane in this case, and then a call to the instance method that actually does the work.

// Header file with "function" as a static class member.
class classname
{
public:
    static DWORD WINAPI function(LPVOID lParameter);
    void callingfunction();
};
 
// cpp file with "function as static class member
#include "StdAfx.h"
#include <iostream>
#include "classname.h"
 
DWORD WINAPI classname::function(LPVOID lParameter)
{
    // Your function here
    return 0;
}
 
void classname::callingfunction()
{
    DWORD id = 0;
    ::CreateThread(NULL, 0, function, this, 0, &id);
}
 
 
>>>>>>>>>>>>>> Other option <<<<<<<<<<<<<
// Header with "function" as global
class classname
{
public:
    void callingfunction();
};
 
// cpp file with "function" as global
#include "StdAfx.h"
#include <iostream>
#include "classname.h"
 
DWORD WINAPI function(LPVOID lParameter)
{
    // Your function here
    return 0;
}
 
void classname::callingfunction()
{
    DWORD id = 0;
    ::CreateThread(NULL, 0, function, this, 0, &id);
}

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LNK2001: unresolved external symbol VCPP 6.0

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