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invalid conversion

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Freaky_Chris Freaky_Chris is offline

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invalid conversion

Oct 16th, 2008

Hi, i'm havnig problem with calling CreateThread. The problem is that it gives me a conversion error from const void* to void*

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
DWORD   dwThreadId;
    HANDLE  myThread; 
 
    myThread = CreateThread( 
            NULL,                   
            0,                       
            MyThreadFunction,      
            "HELLO",           
            0,                      
            &dwThreadId);
DWORD   dwThreadId;
    HANDLE  myThread; 
    
    myThread = CreateThread( 
            NULL,                   
            0,                       
            MyThreadFunction,      
            "HELLO",           
            0,                      
            &dwThreadId);

dwThreadId id is the problem, the function is supose to take a pointer to a DWORD.

Thanks for any help
Cgris

Knowledge is power -- But experience is everything

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Narue

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Re: invalid conversion

Oct 16th, 2008

Post a complete program that exhibits the problem, please. Also post the exact error message rather than summarizing.

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Freaky_Chris Freaky_Chris is offline

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Re: invalid conversion

Oct 16th, 2008

OK, by no means is this safe. It was a meer test to get me started with threads.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <windows.h>
#include <iostream>
 
DWORD WINAPI MyThreadFunction( LPVOID lpParam );
 
int main()
{
    DWORD   dwThreadId;
    HANDLE  myThread; 
 
    myThread = CreateThread( 
            NULL,                   
            0,                       
            MyThreadFunction,      
            "HELLO",           
            0,                      
            &dwThreadId);  
 
    while(1){
             Sleep(3);
             std::cout << "main";
             } 
    std::cin.get();
    return 0;
}
 
DWORD WINAPI MyThreadFunction( LPVOID lpParam ) 
{ 
      std::cout << lpParam;
      while(1){
               Sleep(10);
    std::cout << "thread"; 
    } 
    return 0; 
}
#include <windows.h>
#include <iostream>

DWORD WINAPI MyThreadFunction( LPVOID lpParam );

int main()
{
    DWORD   dwThreadId;
    HANDLE  myThread; 
    
    myThread = CreateThread( 
            NULL,                   
            0,                       
            MyThreadFunction,      
            "HELLO",           
            0,                      
            &dwThreadId);  

    while(1){
             Sleep(3);
             std::cout << "main";
             } 
    std::cin.get();
    return 0;
}

DWORD WINAPI MyThreadFunction( LPVOID lpParam ) 
{ 
      std::cout << lpParam;
      while(1){
               Sleep(10);
    std::cout << "thread"; 
    } 
    return 0; 
}

exact error: 17 invalid conversion from `const void*' to `void*'

Thanks

Last edited by Freaky_Chris; Oct 16th, 2008 at 4:53 pm.

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Narue

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Re: invalid conversion

Oct 16th, 2008

What compiler are you using?

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Re: invalid conversion

Oct 16th, 2008

*cough*
Dev-Cpp

Last edited by Freaky_Chris; Oct 16th, 2008 at 5:02 pm.

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Narue

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Re: invalid conversion

Oct 16th, 2008

I'd be willing to bet that it's the string literal causing you problems. Try this:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <windows.h>
#include <iostream>
 
DWORD WINAPI MyThreadFunction( LPVOID lpParam );
 
int main()
{
  DWORD   dwThreadId;
  HANDLE  myThread;
  char *param = "HELLO";
 
  myThread = CreateThread(
    NULL,
    0,
    MyThreadFunction,
    param,
    0,
    &dwThreadId);
 
  while(1){
    Sleep(3);
    std::cout << "main";
  }
  std::cin.get();
  return 0;
}
 
DWORD WINAPI MyThreadFunction( LPVOID lpParam )
{
  std::cout << lpParam;
  while(1){
    Sleep(10);
    std::cout << "thread";
  }
  return 0;
}
#include <windows.h>
#include <iostream>

DWORD WINAPI MyThreadFunction( LPVOID lpParam );

int main()
{
  DWORD   dwThreadId;
  HANDLE  myThread;
  char *param = "HELLO";

  myThread = CreateThread(
    NULL,
    0,
    MyThreadFunction,
    param,
    0,
    &dwThreadId);

  while(1){
    Sleep(3);
    std::cout << "main";
  }
  std::cin.get();
  return 0;
}

DWORD WINAPI MyThreadFunction( LPVOID lpParam )
{
  std::cout << lpParam;
  while(1){
    Sleep(10);
    std::cout << "thread";
  }
  return 0;
}

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Sci@phy

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Re: invalid conversion

Oct 16th, 2008

•

Originally Posted by Freaky_Chris

*cough*
Dev-Cpp

THIS compiled ok on dev-cpp:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main()
{
    DWORD   dwThreadId;
    HANDLE  myThread; 
    void *ptr=NULL;
 
    myThread = CreateThread( 
            NULL,                   
            0,                       
            MyThreadFunction,      
            ptr,           
            0,                      
            &dwThreadId);  
 
    while(1){
             Sleep(3);
             std::cout << "main";
             } 
    std::cin.get();
    return 0;
}
int main()
{
    DWORD   dwThreadId;
    HANDLE  myThread; 
    void *ptr=NULL;
    
    myThread = CreateThread( 
            NULL,                   
            0,                       
            MyThreadFunction,      
            ptr,           
            0,                      
            &dwThreadId);  

    while(1){
             Sleep(3);
             std::cout << "main";
             } 
    std::cin.get();
    return 0;
}

notice the void* ptr; I suspect problem is in your "HELLO", not in dwThreadId

[edit]And Narue's code compiles on Dev

[/edit]

Last edited by Sci@phy; Oct 16th, 2008 at 5:08 pm.

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Re: invalid conversion

Oct 16th, 2008

Ah that would make much more sense. i did wonder, thanks guys.

i feel like a fool now lol!

Chris

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Sci@phy

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Re: invalid conversion

Oct 16th, 2008

Just to mention, you don't have to declare char ptr, you can simply cast string:
(LPVOID)"HELLO";
But, if you want your string to work inside function that you call, you have to typecast it back to (char*)

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Re: invalid conversion

#10

Oct 16th, 2008

•

Originally Posted by Sci@phy

Just to mention, you don't have to declare char ptr, you can simply cast string:
(LPVOID)"HELLO";
But, if you want your string to work inside function that you call, you have to typecast it back to (char*)

Yes, im aware of both of these, it was just the mere fact i was paying way to much time listening to my god damn compiler / IDE and not enough looking at what i had actually written!

Thanks,
Chris

Knowledge is power -- But experience is everything