CODEWITHSUNDEEP
cpthreads
QPlay
QPlay

Reputation: 3

C - pthread returns unexpected result

I am trying to get to the bottom of an issue with pthreads in C. While my second thread returns the value correctly, the first one just gives me (I assume) a memory address.

The code should do following:

Create a 2 threads which calculate the factorial and the exponential value of a given number from the console.

The Factorial is coded as a function and the exponential calculator is in the main code.

Thanks for any help!

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

void *fac_x(void *x_void_ptr)
{
    int *x_ptr = (int *)x_void_ptr;
    int counter = *x_ptr;

    for (int i = 1; i  < counter ; i++) {
        *x_ptr *= i;
    }
    printf("x factorising finished\n");
    return NULL;
}
int main()
{
    int x,y, counter;
    printf("Enter an integer: ");
    scanf("%d",&x);
    y = x;
    counter = y;

    printf("Input = %d\n",x);

    pthread_t fac_x_thread;

    if(pthread_create(&fac_x_thread, NULL, fac_x, &x)) {

        fprintf(stderr, "Error creating thread\n");
        return 1;
    }
    while (counter != 0) {
        y *= y;
        counter--;
    }
    if(pthread_join(fac_x_thread, NULL)) {
        fprintf(stderr, "Error joining thread\n");
        return 2;
    }
    printf("Factorial: %d \nExponential: %d\n", x, y);

    return 0;
}

Upvotes: 0

Views: 69

Answers (1)

bruno
bruno

Reputation: 32594

the first one just gives me (I assume) a memory address.

this is not an address, you (try to) compute a very great value, you have an overflow very quickly

for 3 it is already 6561 (3*3 = 9, 9*9 = 81, and finaly 81*81=6561)

for 4 the value is 2^32 too great in 32bits (4*4= 16, 16*16 = 256, 256*256 = 65536, and finally 65536*65536 = 4294967296 = 2^32)

for 5 the value is 23283064365386962890625 = 0x4EE2D6D415B85ACEF81 > 2^75 too great for 64b !

Upvotes: 2

Related Questions