I am currently watching course about pointers in C and I have a question about multiple indirection. I understood what multiple indirection is and that is ok, but I ran on piece of code and I tried to do the same thing on a little different way and it is not working, and I wounder why? My question is about pointer casting on line 32, why this doesn't work when I cast it like: printf("Value pointed to by gp is:%s\n",(char *)gp); Here is the code:

#include <stdio.h>

int data[3];
char *words[3];

int main(int argc, char **argv)
{
        void *gp;

        char *word = "rijec";
        printf("%s\n",word);

        for(int i = 0; i < 3;i  )
        {
                data[i] = i;
        }
        words[0] = "zero";
        words[1] = "one";
        words[2] = "two";

        gp = data;
        printf("\nAddress of array data is:%p\n",gp);
        for(int i = 0; i < 3; i  )
        {
                printf("Value pointed to by gp is %d\n",*(int *)gp);
                gp = (int*)gp 1;
        }
        gp=words;
        printf("\nAddress of array of strings words is:%p\n",gp);
        for(int i = 0;i < 3; i  )
        {
                printf("Value pointed to by gp is:%s\n",*(char **)gp);
                gp  = (char **)gp 1;
        }

        return 0;
}

CodePudding user response：

On line 32 gp contains the address where the array words is stored (because the array words decays to pointer during the assignment). The array words consists of 3 pointers. When you cast this to char * you tell the compiler to treat this array as if each of its elements is a char and not a pointer. You need to dereference the pointer to get the actual string.

CodePudding user response：

When you do

gp=words;

words is converted to a pointer to the first element of the array. The first element of the array is a char*. Consequently, words is converted to a char**. So gp will hold a pointer of type char**

That's why this:

printf("Value pointed to by gp is:%s\n",(char *)gp);
                                        ^^^^^^^^
                                        wrong cast

is wrong

and this:

printf("Value pointed to by gp is:%s\n",*(char **)gp);
                                        ^ ^^^^^^^^
                                        |  correct cast
                                        |
                                        correct dereferencing

is correct