A common problem during thread creation: Invalid conversion from 'void * 'to 'void * (*) (void *)

Author: gnuhpc

Source: http://www.cnblogs.com/gnuhpc/

Void main_thread (void * PTR)
{
Char * message1 = "thread 1 ";
Char * message2 = "thread 2 ";
Pthread_t thread3, thread4;
Int iret3, iret4;
Iret3 = pthread_create (& thread3, null, (void *) & print_message_function, (void *) message1 );

Iret4 = pthread_create (& thread4, null, (void *) & print_message_function, (void *) message2 );

}
Void print_message_function (void * PTR)
{
Char * message;
Message = (char *) PTR;
Printf ("% s/n", message );
}
The above code is compiled using G ++ with the following error:
Invalid conversion from 'void * 'to 'void * (*) (void *)
Note that the prototype of the thread function is created in POSIX definition:
Extern int pthread_create (pthread_t * _ restrict _ threadp,
_ Const pthread_attr_t * _ restrict _ ATTR,
Void * (* _ start_routine) (void *),
Void * _ restrict _ Arg) _ Throw;
The third parameter in this call is to load a function. This function has a parameter that can be passed in and returns a common pointer.
Let's take a look at how the original function called this prototype, basically similar to the call method:
(Void *) & main_thread
The meaning of this expression: Take a pointer to the main_thread function and convert it into a common pointer.
This means that the above two things are obviously not the same, so the correct call method is
Iret3 = pthread_create (& thread3, null, print_message_function, (void *) message1 );

The processing function is defined as follows:
Void * print_message_function (void * PTR)