Trying to pass integer argument to thread - c

Question

Hi I am having trouble passing an integer argument to a thread and calculation the factorial using that integer. Here is my code.
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <ctype.h>
void * factorial(void * number) {
int factorial = 1;
int counter = 1;
int newnum = *((int*)number);
printf("%d", newnum);
pthread_exit(NULL);
}
void * sumup( void * number) {
}
int main(int argc, char *argv[]) {
if(argc != 2) {
printf("Argument number error\n");
exit(1);
}
pthread_t thread1;
pthread_t thread2;
int i;
for(i = 0; i < argc; i++){
printf(argv[i]);
printf("\n");
}
int rc;
void * t = argv[1];
rc = pthread_create(&thread1, NULL, factorial, (void*)t );
if (rc != 0) {
printf("There was an error creating the thread\n");
exit(1);
}
pthread_exit(NULL);
exit(0);
}
Right now i am just trying to print the integer sent to get it working properly but here is my output:
./Task1
5
1162608693
It should printing out 5 instead of 1162608693

Answer 1

argv table stores pointers to characters. By doing:
void * t = argv[1];
int newnum = *((int*) t );
what you are trying to print is integer value of string "5". You are passing address of string:
'5' '\0'
casted to pointer to int, therefore you try to read integer value of first sizeof(int) bytes which yields:
5 0 [and you read sizeof(int)-2 bytes out of range]
which results in undefined behavior.
SOLUTION
To convert to integer a string passed as argument to your program use atoi or strtol which does better error checking.