why can argv use increment operator

Question

it's in K&R's book

#include <stdio.h>

main(int argc, char *argv[])
{
    while (--argc > 0)
        printf("%s%s", *++argv, (argc > 1) > " " : "");
    printf("\n");
    return 0;
}

in this book, it says that array can't use increment or decrement operator, in this program ,"argv" should be an array's name, why it can use increment operator?

Answer 1

The second parameter of the main

char *argv[]

is adjusted to pointer to the first element of the array. That is it has type

char **argv;

You may increase pointers.

Thus as initially argv (adjusted to pointer) points to the first element of an array of pointers to strings then ++argv points to the second element of the array and so on.

According to the C Standard (6.7.6.3 Function declarators (including prototypes))

7. A declaration of a parameter as ‘‘array of type’’ shall be adjusted to ‘‘qualified pointer to type’’, where the type qualifiers (if any) are those specified within the [ and ] of the array type derivation.

Answer 2

You are wrong. argv isn't an array. It is a pointer to a pointer to a char. Pointers can be incremented / decremented. And

main(int argc, char *argv[])

is the same as

main(int argc, char **argv)