asked on

Problem by CreateThread() ...

I am going to write a Multi-Thread program in C++. In my program it looks like:

...
...
BOOL CMyService::InitialThreadAndProcess()
{
DWORD dwThreadId, dwThrdParam = 1;
HANDLE hThread;
hThread = CreateThread(
NULL, // no security attributes
0, // use default stack size
CMyService::ThreadFunc, // thread function
&dwThrdParam, // argument to thread function
0, // use default creation flags
&dwThreadId); // returns the thread identifier

if (hThread == NULL)
printf("ok");

CloseHandle( hThread );
return TRUE;
}

DWORD WINAPI CMyService::ThreadFunc( LPVOID lpParam )
{
MessageBox( NULL, "Test", "Thread created.", MB_OK );

return 0;
}

...
...

And the H-file loks like:
...
...
class CMyService
{
...
...
public:
virtual BOOL InitialThreadAndProcess();
DWORD WINAPI ThreadFunc( LPVOID lpParam ) ;
...
...
};

But as I want to compile the program, it shows an error message:
'CreateThread' : Konvertion of Parameters 3 from 'unsigned long (void*)' to 'unsigned long (_stdcall*)(void*) 'Typ2' impossible.

But if I don't use C++ Class but simply in C, i.e. I put the functions all in one file, then there is no problem. Why?

Paul Maker

because the create thread call expects a certain call type, class members are called with thiscall

this is an easy way round

unsigned long _stdcall my_starter(void* ptr)
{
MyService *s = (MyService*)ptr;
ptr->StartFunction();
}

now call create thread passinf this function as the address and pass the object casted to void* in the paramater argument

chenwei

ASKER

I am a little bit confused. Could you be so kind telling me where can I set your code in my program?

Paul Maker

right, at the top of the file that has the source in for the class in question copy this

unsigned long _stdcall my_starter(void* ptr)
{
CMyService *s = (CMyService*)ptr;
ptr->ThreadFunc();
}

then to start a thread

CreateThread(NULL,0,my_starter,(void*)this,0,&dwThreadId);

chenwei

ASKER

Thanks. But i dosen't work. I did what you told me as follow:

// copy the function my_starter at the top of the file
unsigned long _stdcall my_starter(void* ptr)
{
CMyService *s = (CMyService*)ptr;
ptr->ThreadFunc(); }
...
...
BOOL CMyService::InitialThreadAndProcess()
{
..
CreateThread(NULL,0,my_starter,(void*)this,0,&dwThreadId);
..
}

DWORD WINAPI CMyService::ThreadFunc( LPVOID lpParam )
{
...
...
}

But it shows another error message:
C2227: The left part of '->ThreadFunc' muss point to a class/structure/union.

Paul Maker

the new function must go after the header(s) that declares the class

#include.....

new function

class functions

chenwei

ASKER

Yes, I did so.

ASKER CERTIFIED SOLUTION

Paul Maker

membership

This solution is only available to members.

To access this solution, you must be a member of Experts Exchange.

Start Free Trial

chenwei

ASKER

Thanks. But I have to complete some thing, like:

LPVOID lpParam;

unsigned long _stdcall my_starter(void * ptr)
{
CMyService *s = (CMyService*)ptr;
s->ThreadFunc(lpParam);
return 0;
}

Anyway, you get the points.