[SOLVED] A question about local variables in C...

trist007 · 12-26-2011, 05:40 PM

So I run main where I get input via command line. I convert the input to an int with atoi(). Now, is there any way to convert that local variable in main to a global variable so that other functions besides main can access it?

Any tricks for this? Or do I have to bounce around the variable as a pointer from one external function to the next?

trist007 · 12-26-2011, 06:25 PM

I suppose I can make a global pointer, and then have the global pointer point to the local variable after it gets inputed.

MTK358 · 12-26-2011, 06:46 PM

I have no idea what you are talking about, it's so simple:

Code:

int my_global_int;

int main(int argc, char **argv)
{
    my_global_int = atoi(argv[1]);
    
    // do stuff...

    return 0;
}

Unless I didn't understand what you want.

trist007 · 12-26-2011, 06:52 PM

Hehe, I see now. Thanks a ton. Yea that's pretty bad.

trist007 · 12-26-2011, 07:04 PM

Now what if I wanted to have a global integer array but I don't know the number of elements until input in main is made.

Code:

int archive_global[];

int main(int argc, char **argv)
{
      int m;
      m = atoi(argv[1]);
      archive_global[m];

    return 0;
}

This works but it's a little sloppy. Is there a better way?

MTK358 · 12-26-2011, 07:29 PM

Quote:

Originally Posted by trist007

Now what if I wanted to have a global integer array but I don't know the number of elements until input in main is made.

Code:

int archive_global[];

int main(int argc, char **argv)
{
      int m;
      m = atoi(argv[1]);
      archive_global[m];

    return 0;
}

This works but it's a little sloppy. Is there a better way?

It won't work, you're creating a local variable in main() called "archive_global". The only nice way to do this is malloc():

Code:

int *archive_global;
size_t archive_global_count; // if the array's size can vary, it's probably important that the other functions know its size.

int main(int argc, char **argv)
{
    archive_global_count = atoi(argv[1]);
    archive_global = malloc(archive_global_count * sizeof(int));

    // do stuff

    free(archive_global);
    return 0;
}

trist007 · 12-26-2011, 07:57 PM

Awesome, thank you.

trist007 · 12-26-2011, 08:08 PM

I got one more. So say instead of an integer array, it would be an array of pthreads. The same thing would apply? Even though it has a special data type? What if it were type void, still the same?

pthread_t *tid;

int main(void) {
int i;
m = atoi(argv[2]);

tid = malloc(m * sizeof(pthread_t));
for(i = 0; i < m; i++) {
pthread_create(&tid[i], NULL, threadprocess, NULL);
}
// do stuff

for(i = 0; i < m; i++) {
pthread_join(tid[i], NULL)
}

free(tid);
return 0;
}

MTK358 · 12-26-2011, 08:31 PM

Quote:

Originally Posted by trist007

I got one more. So say instead of an integer array, it would be an array of pthreads. The same thing would apply? Even though it has a special data type? What if it were type void, still the same?

Yes, it should be fine.

Also, use code tags to post code. It's much more readable.