invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’ when using pthread in C++

This is a discussion on invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’ when using pthread in C++ within the C Programming forums, part of the General Programming Boards category; Hi, I am using pthread in my main.cpp file and got error in the following code: Code: #include <stdio.h> #include ...

  1. #1
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    invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’ when using pthread in C++

    Hi,
    I am using pthread in my main.cpp file and got error in the following code:
    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <pthread.h>
    
    pthread_mutex_t count_mutex     = PTHREAD_MUTEX_INITIALIZER;
    pthread_mutex_t condition_mutex = PTHREAD_MUTEX_INITIALIZER;
    pthread_cond_t  condition_cond  = PTHREAD_COND_INITIALIZER;
    
    void *functionCount1();
    void *functionCount2();
    int  count = 0;
    #define COUNT_DONE  10
    #define COUNT_HALT1  3
    #define COUNT_HALT2  6
    
    int main()
    {
       pthread_t thread1, thread2;
    
       pthread_create( &thread1, NULL, &functionCount1, NULL);
       pthread_create( &thread2, NULL, &functionCount2, NULL);
       pthread_join( thread1, NULL);
       pthread_join( thread2, NULL);
    
       return 0;
    }
    
    void *functionCount1()
    {
       for(;;)
       {
          pthread_mutex_lock( &condition_mutex );
          while( count >= COUNT_HALT1 && count <= COUNT_HALT2 )
          {
             pthread_cond_wait( &condition_cond, &condition_mutex );
          }
          pthread_mutex_unlock( &condition_mutex );
    
          pthread_mutex_lock( &count_mutex );
          count++;
          printf("Counter value functionCount1: %d\n",count);
          pthread_mutex_unlock( &count_mutex );
    
          if(count >= COUNT_DONE) return(NULL);
        }
    }
    
    void *functionCount2()
    {
        for(;;)
        {
           pthread_mutex_lock( &condition_mutex );
           if( count < COUNT_HALT1 || count > COUNT_HALT2 )
           {
              pthread_cond_signal( &condition_cond );
           }
           pthread_mutex_unlock( &condition_mutex );
    
           pthread_mutex_lock( &count_mutex );
           count++;
           printf("Counter value functionCount2: %d\n",count);
           pthread_mutex_unlock( &count_mutex );
    
           if(count >= COUNT_DONE) return(NULL);
        }
    
    }
    g++ gives error:
    /home/C/test/main.cpp|96|error: invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’|
    /home/C/test/main.cpp|96|error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’|
    /home/C/test/main.cpp|97|error: invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’|
    /home/C/test/main.cpp|97|error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’|
    Could you explain a little bit about these mistakes and how to fix it? Thanks in advance!

  2. #2
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    Your thread functions should take a void * parameter.

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    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  3. #3
    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by matsp View Post
    Your thread functions should take a void * parameter.

    --
    Mats
    And even if you don't need that parameter you still need to declare it. If the compiler whines about "unused parameter" just don't give it a name
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

  4. #4
    CSharpener vart's Avatar
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    Quote Originally Posted by brewbuck View Post
    just don't give it a name
    could you do it in C?
    The first 90% of a project takes 90% of the time,
    the last 10% takes the other 90% of the time.

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    Quote Originally Posted by vart View Post
    could you do it in C?
    I don't think so.

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    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Yes, I have tried to add a parameter to the two functions. It's odd that both
    Code:
    void *functionCount1(void * p)
    void *functionCount2(void * p)
    Code:
    void *functionCount1(int * p)
    void *functionCount2(int * p)
    still result in the same error
    /home/C/test/main.cpp|96|error: invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’|
    /home/C/test/main.cpp|96|error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’|
    /home/C/test/main.cpp|97|error: invalid conversion from ‘void* (*)()’ to ‘void* (*)(void*)’|
    /home/C/test/main.cpp|97|error: initializing argument 3 of ‘int pthread_create(pthread_t*, const pthread_attr_t*, void* (*)(void*), void*)’|
    Seems like the two functions are always recognized as void* (*)(), instead of taking a parameter.

    By the way, I copied this example from Linux Tutorial: POSIX Threads as my first multi-threading program, where the code is C. However I am going to apply it to my C++ code.

  7. #7
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    Did you change your prototypes too?

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  8. #8
    C++まいる!Cをこわせ! Elysia's Avatar
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    Quote Originally Posted by brewbuck View Post
    And even if you don't need that parameter you still need to declare it. If the compiler whines about "unused parameter" just don't give it a name
    I believe in C, you can use...
    (void)unused_param;
    ...instead.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  9. #9
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    Quote Originally Posted by Elysia View Post
    I believe in C, you can use...
    (void)unused_param;
    ...instead.
    Yes - that also works in C++ of course.

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    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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    Did you change your prototypes too?
    My bad. Now it works! Thanks!

    In case my function takes multiple parameters possibly with different types, how to pass them into pthread_create in the last parameter "void * arg"?

  11. #11
    C++まいる!Cをこわせ! Elysia's Avatar
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    Make a struct or class that you pass along.
    Btw, why is this in the C forum when it is C++?
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  12. #12
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    Thanks Elysia!
    Sorry to spam here with C++ stuff. I would be careful next time.

  13. #13
    Maz
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    and one more programmer has been doomed to eternal suffering... Hopefully he knows what is waiting for him. Synchronization problems, deadlocks, sudden crashes due to wild pointers hitting from other threads, harder debugging, starvations, hard to spot performance issues, pain of asm while writing atomic compare and swap...

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