Get size of file on disk

var length = new System.IO.FileInfo(path).Length;

This gives the logical size of the file, not the size on the disk.

I wish to get the size of a file on the disk in C# (preferably without interop) as would be reported by Windows Explorer.

It should give the correct size, including for:

  • A compressed file
  • A sparse file
  • A fragmented file
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According to MSDN social forums:

The size on disk should be the sum of the size of the clusters that store the file:
long sizeondisk = clustersize * ((filelength + clustersize - 1) / clustersize);
You'll need to dip into P/Invoke to find the cluster size; GetDiskFreeSpace() returns it.

See How to get the size on disk of a file in C#.

But please note the point that this will not work in NTFS where compression is switched on.

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最佳答案

This uses GetCompressedFileSize, as ho1 suggested, as well as GetDiskFreeSpace, as PaulStack suggested, it does, however, use P/Invoke. I have tested it only for compressed files, and I suspect it does not work for fragmented files.

public static long GetFileSizeOnDisk(string file)
{
FileInfo info = new FileInfo(file);
uint dummy, sectorsPerCluster, bytesPerSector;
int result = GetDiskFreeSpaceW(info.Directory.Root.FullName, out sectorsPerCluster, out bytesPerSector, out dummy, out dummy);
if (result == 0) throw new Win32Exception();
uint clusterSize = sectorsPerCluster * bytesPerSector;
uint hosize;
uint losize = GetCompressedFileSizeW(file, out hosize);
long size;
size = (long)hosize << 32 | losize;
return ((size + clusterSize - 1) / clusterSize) * clusterSize;
}


[DllImport("kernel32.dll")]
static extern uint GetCompressedFileSizeW([In, MarshalAs(UnmanagedType.LPWStr)] string lpFileName,
[Out, MarshalAs(UnmanagedType.U4)] out uint lpFileSizeHigh);


[DllImport("kernel32.dll", SetLastError = true, PreserveSig = true)]
static extern int GetDiskFreeSpaceW([In, MarshalAs(UnmanagedType.LPWStr)] string lpRootPathName,
out uint lpSectorsPerCluster, out uint lpBytesPerSector, out uint lpNumberOfFreeClusters,
out uint lpTotalNumberOfClusters);
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The code above does not work properly on Windows Server 2008 or 2008 R2 or Windows 7 and Windows Vista based systems as cluster size is always zero (GetDiskFreeSpaceW and GetDiskFreeSpace return -1 even with UAC disabled.) Here is the modified code that works.

C#

public static long GetFileSizeOnDisk(string file)
{
FileInfo info = new FileInfo(file);
uint clusterSize;
using(var searcher = new ManagementObjectSearcher("select BlockSize,NumberOfBlocks from Win32_Volume WHERE DriveLetter = '" + info.Directory.Root.FullName.TrimEnd('\\') + "'") {
clusterSize = (uint)(((ManagementObject)(searcher.Get().First()))["BlockSize"]);
}
uint hosize;
uint losize = GetCompressedFileSizeW(file, out hosize);
long size;
size = (long)hosize << 32 | losize;
return ((size + clusterSize - 1) / clusterSize) * clusterSize;
}


[DllImport("kernel32.dll")]
static extern uint GetCompressedFileSizeW(
[In, MarshalAs(UnmanagedType.LPWStr)] string lpFileName,
[Out, MarshalAs(UnmanagedType.U4)] out uint lpFileSizeHigh);

VB.NET

  Private Function GetFileSizeOnDisk(file As String) As Decimal
Dim info As New FileInfo(file)
Dim blockSize As UInt64 = 0
Dim clusterSize As UInteger
Dim searcher As New ManagementObjectSearcher( _
"select BlockSize,NumberOfBlocks from Win32_Volume WHERE DriveLetter = '" + _
info.Directory.Root.FullName.TrimEnd("\") + _
"'")


For Each vi As ManagementObject In searcher.[Get]()
blockSize = vi("BlockSize")
Exit For
Next
searcher.Dispose()
clusterSize = blockSize
Dim hosize As UInteger
Dim losize As UInteger = GetCompressedFileSizeW(file, hosize)
Dim size As Long
size = CLng(hosize) << 32 Or losize
Dim bytes As Decimal = ((size + clusterSize - 1) / clusterSize) * clusterSize


Return CDec(bytes) / 1024
End Function


<DllImport("kernel32.dll")> _
Private Shared Function GetCompressedFileSizeW( _
<[In](), MarshalAs(UnmanagedType.LPWStr)> lpFileName As String, _
<Out(), MarshalAs(UnmanagedType.U4)> lpFileSizeHigh As UInteger) _
As UInteger
End Function
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I think it will be like this:

double ifileLength = (finfo.Length / 1048576); //return file size in MB ....

I'm still doing some testing for this, to get a confirmation.


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