c++ - 对于卷句柄，来自 FILE_END 的 SetFilePointer 始终失败

Question

我只是想将卷句柄的文件指针从FILE_END向后移动。不幸的是，无论我传递给它的任何输入值如何，操作都会失败!

我使用以下代码:

HANDLE vol_handle = CreateFile ("\\\\.\\C:",
                         GENERIC_READ | GENERIC_WRITE,
                         FILE_SHARE_READ | FILE_SHARE_WRITE,
                         NULL, OPEN_EXISTING, 0, NULL);

if (vol_handle == INVALID_HANDLE_VALUE)
{
    printf("Failed to create volume handle!\n");
    print_last_error(GetLastError());
    return ERROR;
}
printf("Handle acquired for volume %s \n", VOLUME);

long int dist = 512000; // 500 KB forwards

SetLastError(0);
int result = SetFilePointer (vol_handle, dist, NULL, FILE_BEGIN);
if (result == INVALID_SET_FILE_POINTER)
{
    printf("SetFilePointer (BEGIN) FAILED!\n");
    print_last_error(GetLastError());
}
else
    printf("SetFilePointer (BEGIN) SUCCESS!\n");

dist = -5120; // 50 KB backwards

SetLastError(0);
result = SetFilePointer (vol_handle, dist, NULL, FILE_END);
if (result == INVALID_SET_FILE_POINTER)
{
    printf("SetFilePointer (END) FAILED!\n");
    print_last_error(GetLastError());
}
else
    printf("SetFilePointer (END) SUCCESS!\n");

SetLastError(0);
result = SetFilePointer (vol_handle, dist, NULL, FILE_CURRENT);
if (result == INVALID_SET_FILE_POINTER)
{
    printf("SetFilePointer (CURRENT) FAILED!\n", offset_low_part);
    print_last_error(GetLastError());
}
else
    printf("SetFilePointer (CURRENT) SUCCESS!\n");

输出:

  Handle acquired for volume \\.\C:  SetFilePointer (BEGIN) SUCCESS!  SetFilePointer (END) FAILED!     Error 0x57: The parameter is incorrect.  SetFilePointer (CURRENT) SUCCESS!

As you can see, the seek works fine for FILE_BEGIN and FILE_CURRENT, but it always fails for FILE_END with error code 0x57 (87 in decimal) saying:

  The parameter is incorrect

Note that changing dist to a positive value doesn't change the situation.

What am I missing here?

( NOTE: Testing on Windows-5.1.2600 (XP SP3) in latest Code::Blocks IDE 16.01 with MinGW compiler, and Administrator privileges )

---

NOTE: This is absolutely not a duplicate of this question, since I am not accessing physical disk (volume access is different from physical disk) and the distance value is a multiple of 512 bytes (the logical sector size). If the distance length was incorrect, then the other seeks (BEGIN and CURRENT) would have failed as well, yet they don't.

---

Update

Based on Rohans' answer, I performed another check with the following code:

long long int offset_64 = 5120000 // 5000 KB distance;
long int offset_low_part = -(0xffffffff & offset_64);
long int offset_hig_part = offset_64 >> 32;

printf("offset_64 = %lld\n", offset_64);
printf("low_part  = %ld\n", offset_low_part);
printf("high_part = %ld\n\n", offset_hig_part);

// Get volume handle using CreateFile(...) exactly as before;

SetLastError(0);
int result = SetFilePointer (vol_handle, offset_low_part, &offset_hig_part, FILE_END);

if (result == INVALID_SET_FILE_POINTER)
{
    print_last_error(GetLastError());
    printf("Failed to set file pointer!\n");
    printf("high_part after SetFilePointer = %ld\n", offset_hig_part);
    return ERROR;
}

虽然我相信Rohans的观点很重要，但它仍然没有解决问题:

offset_64 = 5120000
low_part  = -5120000
high_part = 0

Handle acquired for volume \\.\C:
Error 0x57: The parameter is incorrect.
Failed to set file pointer!
high_part after SetFilePointer = 0

对 low_part 使用正值不会改变这种情况。

<小时/>

更新

根据下面 David Heffernan 的评论，我承认使用 SetFilePointerEx 可以使这段代码更短、更容易，但结果仍然相同，并且操作无法从 FILE_END 中查找 code> 在音量 handle 上。

Answer 1

这并不奇怪。卷不是文件，因此它没有文件结束位置。

Windows当然可以使用卷长度作为文件末尾位置，但没有特别的理由让它处理这种特殊情况。

您必须自己计算偏移量。