Thread: Beginner's question concerning pointers and arrays

c is an array of char pointers, which means c is actually an array, and that's why you can't use ++ operator with it. Whereas b is a poniter(not an array), that's why ++b is legal. Take this as an example.

Code:

int a[]={1,2,3,4};
printf("%p",(void *)++a); // again the same error coz a is an array

You can do this:

Code:

printf("%s\n", ++(*c));

but that ++ == sizeof(char), which is not what you want.

Consider subscript notation:

Code:

printf("%s\n", c[1]);

> 1) Why is it that I can manipulate argv, which is an array of char pointers, using ++ but couldn't do the same to c (in the original post)?
Because it's a pointer.
char *argv[] could equally be written as char **argv

Using [] in the context of a function parameter doesn't add any "true array" properties to it.

Originally Posted by rcomj

Thanks for the help. I appreciate both of your replies.

I have two further questions about the following code:

Code:

#include <stdio.h>

int main(int argc, char *argv[]) {

  int a[] = {1, 10, 100, 1000};
  int *b = a;
  char *c[] = {"hello", "how", "are", "you?"};
  char **d = c;

  printf("%d\n", *b);
  printf("%d\n", *++b);
  printf("%d\n", *++b);
  printf("%d\n", *++b);

  printf("%s\n", *d);
  printf("%s\n", *++d);
  printf("%s\n", *++d);
  printf("%s\n", *++d);

  while (--argc > 0)
    printf("%s\n", *++argv);

  return 0;
}

1) Why is it that I can manipulate argv, which is an array of char pointers, using ++ but couldn't do the same to c (in the original post)?

2) Is my way of using char **d sloppy at all? After reading BEN10's answer, I had the idea of using a pointer to a pointer to a char, but I don't know if that is a convoluted way of doing things.

My goal with this little program is to understand pointers better and not use indexing, since I already understand how indexing works.

Thanks again for any help.

1. When you use any array as an argument to function it decomposes into pointer and thus you can do ++ with argv. Here's an example.

Code:

#include<stdio.h>
void f(int []);
int main(void)
{
	int a[]={1,2,3};
	printf("%p",(void *)a);
	f(a);
	getch();
}
void f(int b[])
{
	printf("\n%p",(void *)++b);//++ is legal here
}

2. It's fine I guess.