使用带有char指针的函数调用pthread_create

Question

I have a function which takes string. Since pthread don't accept string , i make the function's parameter char pointer. Now I want to call that function with pthread_create but i can not do it. Problem arise because of void * i think. I searched it and make some casting but i cannot succeed. How can i fix it so that it can work under g++

#include <iostream>
#include <cstdlib>
#include <pthread.h>

using namespace std;

#define NUM_THREADS     5

void printString(char *x)
{
    cout << x << endl;
        pthread_exit(NULL);
}

int main ()
{
     pthread_t threads[NUM_THREADS];
     int rc;
     int i;
     string temp = "hello";

  char *bufferG;
  bufferG = new char[temp.size() + 1]; 
  std::copy(temp.begin(), temp.end(), bufferG); 
  bufferG[temp.size()] = '\0'; 

     for( i=0; i < NUM_THREADS; i++ ){
         cout << "main() : creating thread, " << i << endl;
         rc = pthread_create(&threads[i], NULL, printString,  &bufferG ); //(void *) &bufferG also doesn't work
     }
 pthread_exit(NULL);
 }

the error is : thread.cpp: In function 'int main()': thread.cpp:27:69: error: invalid conversion from 'void ( )(char )' to 'void* ( )(void )' [-fpermissive] /usr/include/pthread.h:225:12: error: initializing argument 3 of 'int pthread_create(pthread_t*, const pthread_attr_t*, void* ( )(void ), void*)' [-fpermissive]

Answer 1

The argument expected by pthread_create is,

void *(*)(void *)

that is a pointer to function accepting a void pointer and returning a void pointer .

Change your method to have the following signature:

/*static*/ void* printString(void *x) { ... }

Answer 2

Ok, try this out, now the main thread joins on children to execute and also instead of printing single character within thread fn, we are now using the whole buffer instead

#include <iostream>
#include <cstdlib>
#include <pthread.h>

using namespace std;

#define NUM_THREADS     5

void * printString(void *x)
{
    cout << ((char *)x)<< endl;
}

int main ()
{
     pthread_t threads[NUM_THREADS];
     int rc;
     int i;
     string temp = "hello";

  char *bufferG;
  bufferG = new char[temp.size() + 1]; 
  std::copy(temp.begin(), temp.end(), bufferG); 
  bufferG[temp.size()] = '\0'; 


     for( i=0; i < NUM_THREADS; i++ ){
         cout << "main() : creating thread, " << i << endl;
         rc = pthread_create(&threads[i], NULL, printString,  bufferG ); 
     }
    for( i=0; i < NUM_THREADS; i++ ){
     pthread_join(threads[i], NULL);
    }
 pthread_exit(NULL);
 }