没有 FILE_FLAG_NO_BUFFERING 的 SetFilePointer [英] SetFilePointer without FILE_FLAG_NO_BUFFERING

问题描述

考虑这个程序:

#include <stdio.h>
#include <windows.h>
int main(int argc, char** argv) {
  if (argc != 2)
    return 1;
  HANDLE j = CreateFile("\\\\.\\F:", FILE_GENERIC_READ, FILE_SHARE_WRITE,
    NULL, OPEN_EXISTING, FILE_ATTRIBUTE_SYSTEM, NULL);
  int k = SetFilePointer(j, atoi(argv[1]), NULL, FILE_BEGIN);
  printf("%d\n", k);
}

我得到了这些结果:

> a 512
512

> a 513
-1

> a 1024
1024

所以我只能以卷扇区大小的倍数移动文件指针.这个是 FILE_FLAG_NO_BUFFERING 预期的行为旗帜.但是我没有使用那个标志，那么为什么我会得到这些结果?

So I can only move the file pointer in multiples of the volume sector size. This is the behavior that would be expected with the FILE_FLAG_NO_BUFFERING flag. However I am not using that flag, so why am I getting these results?

推荐答案

您打开了对驱动器卷而不是文件的直接访问.无论缓冲如何，卷的读/写必须是扇区大小的偶数倍.您无法读取/写入部分扇区.

You opened direct access to a drive volume instead of a file. Reads/writes of a volume must be in even multiples of the sector size regardless of buffering. You cannot read/write partial sectors.

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