The Tale of Two pointers in C

by Forrest Sheng Bao http://fsbao.net

The screenplay:

// The Tale of Pointers in C: Demos to refer when using pointers in C
// License: GPL v3.0 
// Author: Forrest Sheng Bao http://fsbao.net Forrest dot His_last_name =aT= gmail.com

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])
{
        printf("\n\t Every story has a beginning.\n\n");
        int i =10;
        int* a = &i;
        printf("\t We have an integer i=%d\n\n", i);
        printf("\t It is stored in memory address %p.\n\n", a);
        printf("\t To access the integer, we dereference the pointer: %d. \n\n", *a);

        printf("\t For strings, it's a different story \n\n");

        char *sdring;
        if (argc > 1)
        {
                sdring = argv[1];
                printf("\t The first parameter of this shell command is %s\n\n", argv[1]);

                printf("\t The first character is: %c.\n\n", *argv[1]);

                printf("\t The second character is: %c.\n\n", *(sdring+1));

                printf("\t The string from the 2nd character is %s.\n\n", sdring+1);

                *(sdring+10) = "Z";

                printf("\t You won't see a Z: %c.\n\n", *(sdring+10));

/*              printf("\t This will cause a segmentation fault %s", *sdring);*/
        }
}

The final show

$ gcc pointer.c
pointer.c: In function ‘main’:
pointer.c:32: warning: assignment makes integer from pointer without a cast
$ ./a.out abcdef

  Every story has a beginning.

  We have an integer i=10

  It is stored in memory address 0xbfe2646c.

  To access the integer, we can dereference the pointer: 10. 

  For strings, it's a different story 

  The first parameter of this shell command is abcdef

  The first character is: a.

  The second character is: b.

  The string from the 2nd character is bcdef.

  You won't see a Z: U.