James Kanze
11/28/2008 7:47:00 PM
uche wrote:
> I am trying to send a pointer to the thread below; however,
> when the thread gets executed, the pointer goes out of scope .
> How do I fix it ?
What is "data"? Is it a data type, or a pointer to a data type?
You seem to use it both ways.
> int mywrite(char* id, int number_of_characters, char char_array)
> {
> HANDLE Producer;
> DWORD ThId;
> //global_char = char_array;
> //create mutual exlusion for producer process to write into the buffer
> //create producer thread and start the function for inserting characters
> //mywriteTh is the entry point of the producer
> ptr =new data;
OK, we have 'data' as a data type, and 'ptr' is, I suppose a
data*.
> ptr->character = char_array;
Again, what is char_array? Where does it come from?
> cout<<ptr->character<<endl;
> ptr->id = id;
> cout<<ptr->id<<endl;
> Producer = (HANDLE) CreateThread (NULL, 0, mywriteTh,
> reinterpret_cast<data> (ptr) , 0, &ThId); // i want to send the
> pointer to this thread
Anytime you need a reinterpret_cast for a function argument, you
should be asking yourself questions. If I understand the
interface description of CreateThread at MSDN (Microsoft seems
to go in a lot for obfuscated typenames), you don't need any
cast at all; just pass the pointer. (I'm guessing here that
LPVOID is a void*; where the L comes from, I don't know.)
> cout<<ptr->id<<endl;
> return 0;
> }
> DWORD WINAPI mywriteTh(data ptr)
And according to the documentation, this function must take a
void* (well, an LPVOID) as well, not a data. (The documentation
shows some __in as well. More obfuscation; I don't think it
means anything.)
> {
> //global_char is available here
> DWORD tId = GetCurrentThreadId();
> data *ptr_data = reinterpret_cast<data *>(ptr); // pointer is goes
> out of scope
Again, a reinterpret_cast is a no-no. You need a static_cast of
the void* to the exact type of the pointer that was converted to
void*, above.
> }
As for "going out of scope", of course the pointer goes out of
scope. But you're passing a copy of it to the thread, and the
memory it points to is still there.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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