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Using CreateThread() function

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Using CreateThread() function

 
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  #1
Jun 12th, 2008
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:
C++ Syntax (Toggle Plain Text) 
  1. void MultiReader::CreateThreads()
  2. {
  3. 	unsigned int nThreadNo;
  4.  
  5. 	for( nThreadNo = 0; nThreadNo < vDirectories.size(); nThreadNo++)
  6. 	{
  7. 		CreateThread( NULL, 0, &MultiReader::ReaderThread, vDirectories.at(nThreadNo).sDirectoryName, 0, NULL);
  8. 	}
  9. }
  10.  
  11. DWORD WINAPI MultiReader::ReaderThread(LPVOID p_pVoid)
  12. {
  13. 	return NULL;
  14. }

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?
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Re: Using CreateThread() function

 
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  #2
Jun 12th, 2008
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.
Don't PM me with questions -- you might get a nasty PM in response. If you have a question then post it in one of the forums.
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Re: Using CreateThread() function

 
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  #3
Jun 12th, 2008
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?
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Re: Using CreateThread() function

 
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  #4
Jun 12th, 2008
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Originally Posted by Cybulski View Post
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.
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Re: Using CreateThread() function

 
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  #5
Jun 12th, 2008
Now I need to do something like this:
C++ Syntax (Toggle Plain Text) 
  1. CreateThread( NULL, 0, &MultiReader::ReaderThread, (void*)vDirectories.at(nThreadNo), 0, NULL);

While vDirectories is:
C++ Syntax (Toggle Plain Text) 
  1. struct OPTIONS
  2. 	{
  3. 		string sDirectoryName;
  4. 		vector<string> vExtensions;
  5. 		int uOperationId;
  6. 	};
  7.  
  8. 	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?
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Re: Using CreateThread() function

 
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  #6
Jun 12th, 2008
The call
C++ Syntax (Toggle Plain Text) 
  1. vDirectories.at(nThreadNo)
will return the reference to the element of the vector. If you will get it address
C++ Syntax (Toggle Plain Text) 
  1. &vDirectories.at(nThreadNo)
and convert to the void pointer
C++ Syntax (Toggle Plain Text) 
  1. (void*)&vDirectories.at(nThreadNo)
the call should be accepted by the compiler.

You can convert the passed pointer back in the thread function
C++ Syntax (Toggle Plain Text) 
  1. DWORD WINAPI MultiReader::ReaderThread(LPVOID p_pVoid)
  2. {<blockquote>OPTIONS* parameter = (OPTIONS*)p_pVoid;
  3. //use structure by pointer</blockquote>}

Also there is a possibility to use the non-static function ReaderThread (needs to include the boost library to your project):
C++ Syntax (Toggle Plain Text) 
  1. CreateThread( <blockquote>NULL, 
  2. 0, 
  3. boost::bind(&MultiReader::ReaderThread,this),
  4. (void*)&vDirectories.at(nThreadNo), 
  5. 0, 
  6. NULL);</blockquote>
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Re: Using CreateThread() function

 
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  #7
Jun 12th, 2008
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.
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Re: Using CreateThread() function

 
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  #8
Jun 13th, 2008
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
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