为什么取消引用内存别名区域的C程序会导致分段错误？

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

int main()
{
    char *myptr = calloc(500,1);
    char *myptr2 = myptr;

    *myptr++ = 'A';
    *myptr++ = 'B';
    *myptr = '\0';
    /* This should dereference the beginning of the memory and print until myptr[2] which is '\0' */
    printf("Myptr2 points to: %s\n", *myptr2);

    free(myptr);

    return(EXIT_SUCCESS);
}

为什么第13行（printf行）创建SIGSEV？它应该指向内存的开始，然后printf应该打印直到它到达'\ 0'。