我用的是Visual Studio 2017。

正常情况下代码如下

#include<stdio.h>
#include<conio.h>
int main()
{
    char f1_name[4096], f2_name[4096];
    unsigned long long *ip1, *ip2, *ipe1 = (unsigned long long*)(f1_name + 4096);

    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
        *ip1 = *ip2 = 0;
    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
        printf("%llX %llX\n", *ip1, *ip2);
    return 0;
}

输出是两列0。

在赋值前加入输出代码后代码如下

#include<stdio.h>
#include<conio.h>
int main()
{
    char f1_name[4096], f2_name[4096];
    unsigned long long *ip1, *ip2, *ipe1 = (unsigned long long*)(f1_name + 4096);

    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
    {
        printf("%llX %llX\n", *ip1, *ip2);
    };
    getchar();

    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
        *ip1 = *ip2 = 0;
    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
    {
        printf("%llX %llX\n", *ip1, *ip2);
    }
    return 0;
}

为什么在加入代码后输出的第二列不是0，而是一列相同的数字（每次运行不一定一样），例如63006200610060、67006600650064、6B006A00690068？

#include<stdio.h>
#include<conio.h>
int main()
{
    char f1_name[4096], f2_name[4096];
    unsigned long long *ip1, *ip2, *ipe1 = (unsigned long long*)(f1_name + 4096);

    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
    {
        printf("%llX %llX\n", *ip1, *ip2);    //默认是输出字符串f1_name，f2_name,  他们没有初始化，所以出现的是乱码
    };
    getchar();

    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
        *ip1 = *ip2 = 0;            //这是给字符串f1_name，f2_name赋值，所有的值都设置为0
    ip1 = (unsigned long long*)f1_name;
    ip2 = (unsigned long long*)f2_name;
    for (; ip1 < ipe1; ip1++, ip2++)
    {
        printf("%llX %llX\n", *ip1, *ip2);        //这里的输出字符串f1_name，f2_name，即输出0
    }
    return 0;
}

我说的是第二个printf语句输出的第二列不是0。为什么不是0我现在还不清楚，不过生成64位程序输出的都是0，生成32位的第二列就不是0。

我使用的是gcc 32位的编译，第二次使用输出的的都是0

为什么不是0呢？因为f1_name  f2_name没有赋值；你只是给ip1  ip2赋值一下，然后又将ip1   ip2赋值给f2_name   f1_name了；所以编译器随便给你一个值；
如果你在*ip1 = *ip2 = 0;哪里断点一下呢？

是这样吗