Passing data to Pthread using structure in C - c

Question

I want to run Pthreads in c. i am comfortable with sending integer values to Pthread in c. But when I am passing the data structure to the thread, it is printing garbage values.
My code is as follows:
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define NUMBER_OF_THREADS 3
typedef struct MyStructure
{
int id;
char *myName;
}myst;
void *PrintHello(void *threadArgs)
{
myst *myPersonalSt;
myPersonalSt = (myst *) threadArgs;
printf("Thread %d and Name : %s \n", myPersonalSt->id ,
myPersonalSt->myName);
pthread_exit(NULL);
}
int main(int argc, char *argv[])
{
pthread_t threads[NUMBER_OF_THREADS];
long taskids[NUMBER_OF_THREADS];
int rc, t;
char myNameArray[NUMBER_OF_THREADS][100] = {"kp" , "kkp" , "ap"};
myst **mystArray;
mystArray = (myst **)malloc(NUMBER_OF_THREADS*sizeof(myst));
for(t=0;t<NUMBER_OF_THREADS;t++)
{
mystArray[t] = (myst *)calloc(1,sizeof(myst));
mystArray[t]->id = t+1;
mystArray[t]->myName = myNameArray[t];
}
for(t=0;t<NUMBER_OF_THREADS;t++) {
printf("Creating thread %d\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello,
(void *) mystArray);
if (rc) {
printf("ERROR; return code from
pthread_create() is %d\n", rc);
exit(-1);
}
}
for(t=0;t<NUMBER_OF_THREADS;t++) {
pthread_join(threads[t],NULL);
}
pthread_exit(NULL); // this takes an input parameter !
}
I was thinking that it was a problem with MALLOC (because it doesn't initialize memory allocated). So I used CALLOC , but the same problem occured.

Answer 1

rc = pthread_create(&threads[t], NULL, PrintHello,
(void *) mystArray);
You're missing the array index here, you mean mystArray + t.
On a side note: remove all these casts, they make the code hard to read. void * is generic and implicitly convertible in c.

Answer 2

This line is wrong:
rc = pthread_create(&threads[t], NULL, PrintHello,
(void *) mystArray);
Given how you're written the rest of the code, it should be:
rc = pthread_create(&threads[t], NULL, PrintHello,
(void *) ( mystArray[t] ) );
But the use of malloc()/calloc() is unnecessary:
myst mystArray[ NUMBER_OF_THREADS ];
memset( mystArray, 0, sizeof( mystArray ) );
...
rc = pthread_create(&threads[t], NULL, PrintHello,
(void *) &( mystArray[t] ) );
That will work without the malloc()/calloc().