Need help for int args (threads) - c

Question

I'm trying to edit this code to work with ints parameters:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>
void* worker (void* param) {
int* nr = (int *) param;
printf ("I got: %d\n",nr);
}
int main (int argc, int *argv[])
{
pthread_t th;
int i;
for(i=1;i<argc;i++){
pthread_create (&th, NULL, worker,(void*)argv[i]);
pthread_join (th, NULL);
}
}
This is not working, smth about pointers, I don't understand. Can anyone explain me? I don't want to use "atoi" function.
For number 5 and 2 I get: -1078000975,-1078000973 and a warning:
11:3: warning: format ‘%d’ expects argument of type ‘int’, but argument 2 has type ‘int *’ [-Wformat=]
printf ("I got: %d\n", nr);
^

Answer 1

A few issues:
argv should be written char * argv[], not int * argv[].
Your (void *) cast in your pthread_create() call is unnecessary.
Your thread function should return a void *.
atoi(), or its more capable cousin, strtol(), is exactly what you're looking for, here. You can either use them, or convert your strings manually, which is suboptimal.
Here's a working version:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
void * worker (void * param)
{
char * numstr = param, * endptr;
long num = strtol(numstr, &endptr, 0);
if ( *endptr ) {
printf("Invalid number.\n");
}
else {
printf ("I got: %ld\n", num);
}
return NULL;
}
int main (int argc, char *argv[])
{
pthread_t th;
for ( int i = 1; i < argc; ++i ) {
pthread_create (&th, NULL, worker, argv[i]);
pthread_join (th, NULL);
}
return 0;
}
and some sample output:
paul#horus:~/src/sandbox$ ./trd 5 haha 10
I got: 5
Invalid number.
I got: 10
paul#horus:~/src/sandbox$

Answer 2

If the arguments you recieve are smaller than 10, you can do this:
pthread_create (&th, NULL, worker,(void*)(argv[i][0]-'0'));
This can be done because ASCII numbers begin at 48 ('0' value). So if you receive a '7' (55 ascii number), you can subtract the '0' to get it: 55-48=7.
If the arguments can be 10 or greater, you must use atoi or a self-implementation of that function, as you can not cast from char* to int in C.
There is another problem with your code, you try to print an int*, which is only a variable that contains a memory address. You should recieve it as an int:
void* worker (void* param)
{
int nr = (int) param;
printf ("I got: %d\n",nr);
}
EDIT:
So your code should look like this:
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <string.h>
void* worker (void* param) {
int nr = (int) param;
printf ("I got: %d\n",nr);
}
int main (int argc, char *argv[])
{
pthread_t th;
int i;
for(i=1;i<argc;i++){
pthread_create (&th, NULL, worker,(void*)(argv[i][0]-'0'));
pthread_join (th, NULL);
}
}
It works for me...

Answer 3

You should pass the pointer to the string and then manipulate it.
pthread_create (&th, NULL, worker, argv[i]); //cast is not required
void* worker (void* param) {
char* nr = param ;
Now you got your string in the thread. Get the first character, and convert it to an integer.
int n = nr[0]-'0' ;
printf ("I got: %d\n",n);
}