Linux and C, program errors - c

Question

I'm trying to alter a bit a code to use 'threads' instead of 'forks'. This is the code I have come up with, but there's an error message, and I'm unsure why.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <pthread.h>
#define N 2 /* define the total number of processes we want */
/* Set global variable */
float total=0;
/* compute function just does something. */
int compute()
{
int i;
float oldtotal=0, result=0;
/* for a large number of times just square root and square
the arbitrary number 1000 */
for(i=0;i<2000000000;i++)
{
result=sqrt(1000.0)*sqrt(1000.0);
}
/* Print the result should be no surprise */
printf("Result is %f\n",result);
/* We want to keep a running total in the global variable total */
oldtotal = total;
total = oldtotal + result;
/* Print running total so far. */
printf("Total is %f\n",total);
return(0);
}
void* thread_procedure(void* param)
{
int i = (int)param;
/* give a message about the proc ID */
printf("Process Id for process %d is %d\n",i,getpid());
/* call the function to do some computation. If we used sleep
The process would simply sleep. We do not want that */
compute();
return NULL;
}
int main()
{
int i, j;
pthread_t thread[N];
float result=0;
printf("\n"); /* bit of whitespace */
/* We want to loop to create the required number of processes
Note carefully how only the child process is left to run */
for(i=0;i<N;i++)
{
/* start new thread and catch it if it/one fails */
j = pthread_create(&thread[i], NULL, &thread_procedure, (void*)i);
if (j)
{
printf("Error");
exit(1);
}
}
/* joining with threads */
for(i=0;i<N;i++)
pthread_join(thread[i], NULL);
/* nothing else to do so end main function (and program) */
return 0;
}
This is the error that I receive, which I am not understanding
practical2b.c: In function ‘thread_procedure’:
practical2b.c:39:10: warning: cast from pointer to integer of different size
[-Wpointer-to-int-cast]
int i = (int)param;
^
practical2b.c: In function ‘main’:
practical2b.c:62:59: warning: cast to pointer from integer of different size
[-Wint-to-pointer-cast]
j = pthread_create(&thread[i], NULL, &thread_procedure, (void*)i);
^
/tmp/cc9tHCVO.o: In function `main':
practical2b.c:(.text+0x11c): undefined reference to `pthread_create'
practical2b.c:(.text+0x168): undefined reference to `pthread_join'
collect2: error: ld returned 1 exit status

Answer 1

After fixing all the errors/warnings raised by the compiler
and incorporating some of the earlier comments,
this is what the code would look like:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <pthread.h>
#include <sys/types.h>
#include <unistd.h>
#define N 2 /* define the total number of processes we want */
/* Set global variable */
float total=0.0f;
/* compute function just does something. */
int compute()
{
int i;
float result=0.0f;
/* for a large number of times just square root and square
the arbitrary number 1000 */
for(i=0;i<2000000000;i++)
{
result=sqrt(1000.0)*sqrt(1000.0);
}
/* Print the result should be no surprise */
printf("Result is %f\n",result);
/* We want to keep a running total in the global variable total */
total += result;
/* Print running total so far. */
printf("Total is %f\n",total);
return(0);
} // end function: compute
void* thread_procedure(void* param)
{
int i = *(int*)param;
/* give a message about the proc ID */
printf("Process Id for process %d is %d\n",i,getpid());
/* call the function to do some computation. If we used sleep
The process would simply sleep. We do not want that */
compute();
return NULL;
}
int main()
{
int i, j;
pthread_t thread[N];
printf("\n"); /* bit of whitespace */
/* We want to loop to create the required number of processes
Note carefully how only the child process is left to run */
for(i=0;i<N;i++)
{
/* start new thread and catch it if it/one fails */
j = pthread_create(&thread[i], NULL, &thread_procedure, (void*)&i);
if (j)
{
printf("Error");
exit(1);
}
}
/* joining with threads */
for(i=0;i<N;i++)
pthread_join(thread[i], NULL);
/* nothing else to do so end main function (and program) */
return 0;
} // end function: main