Question

I am wondering what am I doing wrong here? I cast the void pointer into a struct buffer and it only prints out garbage. Shouldn’t buffer now point to ptr that is a pointer back to the original buffer that we allocated memory for?

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

 struct buffer{
         int a;
         char *string[];
 }buffer;

 void thread1_function(void *ptr){
         struct buffer *buffer=(struct buffer*)ptr;

         printf("hello world\n");

         printf("%s-%n\n", buffer->string,buffer->a);

 }

 int main(){

        struct buffer *buffer;
        int err;
        buffer = (struct buffer*)malloc((11*sizeof(char))+sizeof(int));
        pthread_t thread1;
        sprintf(buffer->string,"%s","strint");
        buffer->a=1;
        printf("main: %s - %d\n",buffer->string,buffer->a);
        err = pthread_create(&thread1, NULL, thread1_function, &buffer);
        printf("error: %d\n",err);
        pthread_join(thread1,NULL);
        return 0;
 }

~

Answer 1

You pass the pointer to the pointer to the struct to your thread. Try passing the pointer to the struct instead. 😉

err = pthread_create(&thread1, NULL, thread1_function, &buffer);

becomes

err = pthread_create(&thread1, NULL, thread1_function, buffer);

EDIT:
Found another mistake: printf("...%n") in the thread function. %n indicates to store the number written so far into the position, the int* parameter at that position points to. You obviously mean %d there, as in your main().