C - ポインタ変数に対するconst宣言

const.c

#include <stdio.h>

int main(int argc, const char *argv[])
{
    int i = 10;
    int j = 20;
    const int *p = &i;
    int * const q = &i;
    const int * const r = &i;

    /**** const type *var ****/

    puts("");
    printf("*p = %d\n", *p);
    printf(" p = %p\n", p);

    /* error */
    /* *p = 100; */

    /* allowed */
    p = &j;

    puts("");
    printf("*p = %d\n", *p);
    printf(" p = %p\n", p);

    /* error */
    /* *p = 100; */

    /**** type * const var ****/

    puts("");
    printf("*q = %d\n", *q);
    printf(" q = %p\n", q);

    /* error */
    /* q = &j; */

    /* allowed */
    *q = 100;

    puts("");
    printf("*q = %d\n", *q);
    printf(" q = %p\n", q);

    /**** const type * const var ****/

    puts("");
    printf("*r = %d\n", *r);
    printf(" r = %p\n", r);

    /* error */
    /* *r = 100; */

    /* error */
    /* r = &j; */

    return 0;
}