Using CreateThread() function

[Cybulski]

I'm trying to call this function requested times. All functions and variables are members of one class, access is public. So, I'm calling like this:

void MultiReader::CreateThreads()
{
	unsigned int nThreadNo;

	for( nThreadNo = 0; nThreadNo < vDirectories.size(); nThreadNo++)
	{
		CreateThread( NULL, 0, &MultiReader::ReaderThread, vDirectories.at(nThreadNo).sDirectoryName, 0, NULL);
	}
}

DWORD WINAPI MultiReader::ReaderThread(LPVOID p_pVoid)
{
	return NULL;
}

And I get this:

error C2664: 'CreateThread' : cannot convert parameter 3 from 'DWORD (__stdcall MultiReader::* )(PVOID)' to 'LPTHREAD_START_ROUTINE'
        There is no context in which this conversion is possible

Can anyone point my error? Suggestion maybe?

[Ancient Dragon]

two problems:
1) ReaderThread must be a static method of the class

2) remove the & &MultiReader::ReaderThread, . Like arrays all you need is the name of the method.

[Cybulski]

Yep, that's it. I tried to figure it out for days. & was there just because compiler suggested me to put it there. That thing is solved, thank you very much.

Now parameter 4: it should be &adress of this string, amirite?

[mitrmkar]

Now parameter 4: it should be &adress of this string, amirite?

Basically a pointer (cast to void *) to anything you want the thread routine to receive via p_pVoid argument.

[Cybulski]

Now I need to do something like this:

CreateThread( NULL, 0, &MultiReader::ReaderThread, (void*)vDirectories.at(nThreadNo), 0, NULL);

While vDirectories is:

struct OPTIONS
	{
		string sDirectoryName;
		vector<string> vExtensions;
		int uOperationId;
	};

	vector<OPTIONS> vDirectories;

But error C2440: 'type cast' : cannot convert from 'DirectoryReader::OPTIONS' to 'void *' All I can cast to (void*) is sDirectoryName.c_str(), even casting integer results in runtime error. Shouldn't be structure fully capable of casting to void type?

[writem]

The call

vDirectories.at(nThreadNo)

will return the reference to the element of the vector. If you will get it address

&vDirectories.at(nThreadNo)

and convert to the void pointer

(void*)&vDirectories.at(nThreadNo)

the call should be accepted by the compiler.

You can convert the passed pointer back in the thread function

DWORD WINAPI MultiReader::ReaderThread(LPVOID p_pVoid)
{
[INDENT]OPTIONS* parameter = (OPTIONS*)p_pVoid;
//use structure by pointer[/INDENT]
}

Also there is a possibility to use the non-static function ReaderThread (needs to include the boost library to your project):

CreateThread( 
[INDENT]NULL, 
0, 
boost::bind(&MultiReader::ReaderThread,this),
(void*)&vDirectories.at(nThreadNo), 
0, 
NULL);[/INDENT]

[Cybulski]

I managed to make compiler accept parameter using &vDirectories.at(nThreadNo) but I missed that litte (void*). Thank you very much, good sir!

Threading almost solved for me.

[Cybulski]

Everything ok with this function now, I mark this thread as solved and continue being problematic in this thread:
http://www.daniweb.com/forums/thread127041.html