Thread is showing inconsistence result - c++

Question

I am creating 5 thread here using ThrdFunc. Here each thread update the listBox.
I was expecting message in this way. Initially come in this way but after some time
Thread1:Adding msg
Thread2:Adding msg
Thread3:Adding msg
But after some time I get message like
Thread0:Adding msg
Thread18967654:Adding msg
Thread18967654:Adding msg
Thread18967654:Adding msg
This is the code:
for (int i = 0;i<6;i++)
{
nThreadNo = i+1;
hWndProducer[i] = CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)ProducerThrdFunc,(void*)&nThreadNo,0,&dwProducerThreadID[i]);
if (hWndProducer[i] == NULL)
{
//ErrorHandler(TEXT("CreateThread"));
ExitProcess(3);
}
}
DWORD WINAPI ThrdFunc ( LPVOID n )
{
int *nThreadNo = (int*)n;
char chThreadNo[3];
memset(chThreadNo,0,3);
while(1)
{
itoa(*nThreadNo,chThreadNo,10);
char* pMsg1 = new char[100];
char* pMsg2 = new char[100];
memset(pMsg1,0,100);
memset(pMsg2,0,100);
strcpy(pMsg1," Thread No:");
strcat(pMsg1,chThreadNo);
strcat(pMsg1," Adding Msg:");
PostMessage(stThreadInfoProd.hWndHandle,UWM_ONUPDATEPRODUCERLIST,(WPARAM)pMsg1,0);
}
return 0;
}

Answer 1

Most likely nThreadNo is allocated on the stack. You're giving each thread a pointer to one of it's elements.
Once the function creating the threads returns, the array is no longer valid, but the thread functions are still pointing to it. The memory the threads are holding pointers to will most likely be overwritten, causing what was originally the thread ID to be overwritten with garbage.
Anything you pass another thread should generally be allocated on heap, either via malloc type functions or new, preferably new since this is C++.
For example, instead of int nThreadNo[6], use int* nThreadNo = new int[6]. However, keep in mind that you will have to delete[] the memory nThreadNo points to when you're done with it.

Answer 2

Well, I can't be sure because you've not given all your code.
However, it looks like nThreadNo is a local variable, defined on the stack of the main thread. You are passing the address of this variable to the threads, but you should be passing the value, or passing some heap allocated memory.
What you are doing is morally equivalent to returning from a function a pointer to a local variable, e.g.
int* foo()
{
int i;
return &i;
}
The simplest way to make your code behave is to make the following changes:
CreateThread(..., (void*)nThreadNo, ...
int nThreadNo = (int)n;

Answer 3

nThreadNo has to be global because you are giving a pointer to it to your new thread.