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thread problem

Posted on 1998-08-14
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Last Modified: 2010-04-01
this is the problem...
i start three threads with the _beginthreadex function
when sending integers values to thread function it works
perfect. But i need to send strings(char *) when i do that
the parameters tend to be the same in all three threads.
wtf is wrong?
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Question by:webrage
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7 Comments
 
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Accepted Solution

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nietod earned 200 total points
ID: 1170281
answer coming.
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LVL 22

Expert Comment

by:nietod
ID: 1170282
you are probably "reusing" the string buffer (that memory stores the string) for each case, right?  Like

char Str[100];

strcpy(Str,"Thread A's message.");
BeginThreadA(Str);
strcpy(Str,"Thread B's message.");
BeginThreadB(B);
strcpy(Str,"Thread C's message.");
BeginThreadC(C);

Something like that?
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LVL 22

Expert Comment

by:nietod
ID: 1170283
What is happening is that the new thread doesn't start right away or doesn't use its parameter (the pointer to the string) right away.  Then you go and alter the string for the next thread.  The the new thread uses the string and finds the new value, not the old one.

Make sense?

What to do about this.  That depends.  One approach would be to dynamically allocate (new) strings to be passed to each thread.  Then each thread would destroy (delete) each string when it was no longer needed.  (The code that allocates the string cannot delete it.  That would be another case of the same problem.)  There may be a better (easier) solution, depending on your circumstances, but that will work.

Let me know if you have questions.
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Author Comment

by:webrage
ID: 1170284


yes maybe i have created a linked list..
the linked list have a char *directory  
but i declare memory for all elements.
i also have startthread function in the linked list

startthread(){
 printf(directory); //here it prints the right value..
 beginthread(directory,thrfunc);
}

thrfunc((void *)ch){
 printf("%s",(char *)ch); //here it doesnt..
}
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Author Comment

by:webrage
ID: 1170285
oh great it now works
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LVL 22

Expert Comment

by:nietod
ID: 1170286
I did not understand your comment about the linked list, etc.   Do I need to or is everything okay now?  If you need more help, try to explain that again.
0
 

Author Comment

by:webrage
ID: 1170287
no it works perfectly now.. I didnt planned to send that message!Sorry..
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