realloc.cpp

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

int main()
{
    int *i = (int *)malloc(sizeof(int));
    i[0] = 12;
    printf("%p  %d", i, i[0]);
    // reserve memory for two integers
    int *p = (int *)malloc(2 * sizeof(int));
    p[0] = 1;
    p[1] = 2;

    // resize memory to hold four integers
    p = (int *)realloc(p, 4 * sizeof(int));
    p[2] = 3;
    p[3] = 4;

    // resize memory again to hold two integers
    p = (int *)realloc(p, 2 * sizeof(int));

    printf("address=%p, value=%d\n", p + 0, *(p + 0)); // valid
    printf("address=%p, value=%d\n", p + 1, *(p + 1)); // valid

    printf("address=%p, value=%d\n", p + 2, *(p + 2)); // INVALID
    printf("address=%p, value=%d\n", p + 3, *(p + 3)); // INVALID

    return 0;
}