代码在下面

当输入58个字符时，报错，输入56个却没有。
单buffer长度只有50
为什么？？

[ 本帖最后由 d1003577678 于 2015-4-13 13:13 编辑 ]

void good()
{
    FILE *fp;
    char name[20], phone[20];
    puts("Win!");
    printf("Your name: ");
    scanf("%s", name);
    printf("Your phone number: ");
    scanf("%s", phone);
    fp = fopen("/home/ving/winner_A","ab+");
    fprintf(fp,"%s\t%s\n",name,phone);
    fclose(fp);
}

void bad()
{
    printf("I'm sorry, you're at %p and you want to be at %p\n", bad, good);
}

int main(int argc, char **argv)
{
    void (*fp)(void) = bad;
    char buffer[50];

    if(argc != 2 || strlen(argv[1]) < 4)
        return 0;

    memcpy(buffer, argv[1], strlen(argv[1]));
    memset(buffer, 0, strlen(argv[1]) - 4);

    fp();

    return 0;
}

applicant@t:~$ ./Problem_A aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa0x4007ad
Segmentation fault (core dumped)
applicant@t:~$ ./Problem_A aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa4007ad
I'm sorry, you're at 0x400848 and you want to be at 0x4007ad

Your task is to change the function pointer fp's value from function bad to function good.
Stack overflow is your chance.