Ad:

C++ Discussion Thread
Marked Solved
Views: 1126

Oct 16th, 2008

invalid conversion

Expand Post »

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

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

Similar Threads

Invalid conversions while using other people's software in C++
need help w/ 'invalid conversion' in C++
Convert first character from lowercase to uppercase? in C
C++ program using classes in C++
Is this how to read in char only in C++

Freaky_Chris

Reputation Points: 325

Solved Threads: 118

Master Poster

Offline

702 posts
since Apr 2008

Permalink

Oct 16th, 2008

Re: invalid conversion

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

Narue

Administrator

Reputation Points: 6442

Solved Threads: 1393

Bad Cop

Offline

11,807 posts
since Sep 2004

Permalink

Oct 16th, 2008

Re: invalid conversion

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

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.

Freaky_Chris

Reputation Points: 325

Solved Threads: 118

Master Poster

Offline

702 posts
since Apr 2008

Permalink

Oct 16th, 2008

Re: invalid conversion

What compiler are you using?

Narue

Administrator

Reputation Points: 6442

Solved Threads: 1393

Bad Cop

Offline

11,807 posts
since Sep 2004

Permalink

Oct 16th, 2008

Re: invalid conversion

*cough*
Dev-Cpp

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

Freaky_Chris

Reputation Points: 325

Solved Threads: 118

Master Poster

Offline

702 posts
since Apr 2008

Permalink

Oct 16th, 2008

Re: invalid conversion

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

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;
}

Narue

Administrator

Reputation Points: 6442

Solved Threads: 1393

Bad Cop

Offline

11,807 posts
since Sep 2004

Permalink

Oct 16th, 2008

Re: invalid conversion

Click to Expand / Collapse Quote originally posted by Freaky_Chris ...

*cough*
Dev-Cpp

THIS compiled ok on dev-cpp:

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.

Sci@phy

Reputation Points: 110

Solved Threads: 43

Posting Whiz in Training

Offline

279 posts
since Sep 2008

Permalink

Oct 16th, 2008

Re: invalid conversion

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

i feel like a fool now lol!

Chris

Freaky_Chris

Reputation Points: 325

Solved Threads: 118

Master Poster

Offline

702 posts
since Apr 2008

Permalink

Oct 16th, 2008

Re: invalid conversion

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*)

Sci@phy

Reputation Points: 110

Solved Threads: 43

Posting Whiz in Training

Offline

279 posts
since Sep 2008

Permalink

Oct 16th, 2008

Re: invalid conversion

Click to Expand / Collapse Quote 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

Freaky_Chris

Reputation Points: 325

Solved Threads: 118

Master Poster

Offline

702 posts
since Apr 2008

This thread is solved

Either the thread starter or a moderator has marked this thread as solved. You can most likely trust the responses and answers given. There is most likely no reason for any further responses to be posted here. If you have a related question, please start a new thread in this forum instead.

This thread is more than three months old

No one has posted to this discussion for at least three months. Please let old threads die and do not reply to them unless you feel you have something new and valuable to contribute that absolutely must be added to make the discussion complete. Otherwise, please start a new thread in this forum instead.

Previous Thread in C++ Forum Timeline: rock paper scissor program

Next Thread in C++ Forum Timeline: Inserting a node on a Tree

DaniWeb Message

Cancel Changes

User Name
Password