C++ 與 C 中的函數(shù)指針

相關(guān)代碼

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>

void *print_message_function( void *ptr );

main()
{
     pthread_t thread1, thread2;
     const char *message1 = "Thread 1";
     const char *message2 = "Thread 2";
     int  iret1, iret2;

     iret1 = pthread_create( &thread1, NULL, print_message_function, (void*) message1);
     if(iret1)
     {
         fprintf(stderr,"Error - pthread_create() return code: %d\n",iret1);
         exit(EXIT_FAILURE);
     }

     iret2 = pthread_create( &thread2, NULL, print_message_function, (void*) message2);
     if(iret2)
     {
         fprintf(stderr,"Error - pthread_create() return code: %d\n",iret2);
         exit(EXIT_FAILURE);
     }

     printf("pthread_create() for thread 1 returns: %d\n",iret1);
     printf("pthread_create() for thread 2 returns: %d\n",iret2);

     pthread_join( thread1, NULL);
     pthread_join( thread2, NULL); 

     exit(EXIT_SUCCESS);
}

void *print_message_function( void *ptr )
{
     char *message;
     message = (char *) ptr;
     printf("%s \n", message);
}

疑惑地方

在函數(shù) pthread_create(pthread_t * thread, const pthread_attr_t * attr,void * (*start_routine)(void *), void *arg);
其中 void * (*start_routine)(void *) 這個(gè)參數(shù)是 "函數(shù)指針"
而根據(jù)函數(shù) void *print_message_function( void *ptr );原型來看這是一個(gè) 返回任何指針類型的函數(shù),不是函數(shù)指針，而且這個(gè)函數(shù)的實(shí)現(xiàn)中并沒有返回值. 但是可以使用gcc編譯通過，沒有任何異常, 有哪位知道這是為什么嗎？ 或者給出一個(gè)參考鏈接？

我所知道的類似void *print_message_function( void *ptr ); 函數(shù)的用法是這樣的

 #include<stdio.h>

 void *test_f(int *n);
 
 int main(void) 
{
         int test_num = 32;
         int *test_p = &test_num;
         int *ret_v = test_f(test_p);
         printf("%d \n",*ret_v);
         return 0;
 }

void *test_f(int *n) 
{
         *n = *n + 1;
         return n;
}