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WriteFile() Win32 call with input buffer size = 512 Fails., when i try to write to the disk that has bytes per sector = 4096.[3 TB disk]. Same WriteFile with input buffer size = 4096 works fine.,

Can any body explain this behavior.


This what the call is.,

res &= WriteFile(hFile, m_Footer,sizeof(VHDFooter), &dwNumBytes, NULL);

hFile - Handle of a VHD File.,

m_Footer - VHD File Footer.,

sizeof(VHDFooter) = 512 always .,

dwNumBytes = o/p buffer.,

My Create File looks like this:
hFile = _CreateFile(szImageFile, GENERIC_WRITE | GENERIC_READ, 


res &= WriteFile(hFile, m_Footer, sizeof(VHDFooter), &dwNumBytes, NULL);// Fails with last error  = 87

res &= WriteFile(hFile, m_Footer,4096, &dwNumBytes, NULL); // Success., if input buffer size= 4096

Disk property.,4096 bytes per sector.,

NOTE: For 512 bytes per sector., the first function call works well.,


Updated 5-Mar-13 21:08pm
Michael Haephrati 4-Mar-13 16:11pm    
What exactly is your error code?
gssajith87 6-Mar-13 2:09am    
question improved., 87 is the last error i get.,
jan.mach71 6-Mar-13 2:47am    
If it's decimal 87 then check this: , but as your snippet does not have any overlapped, it seems you will have to investigate and find solution yourself. Just a note: you are quick at changing sector sizes:)

Hi Thanks all,

I was passing the handle to writeFile which was created by CREATEFILE with FILE_FLAG_NO_BUFFERING attribute, MSDN has clean link saying that, if i have a handle passed to writefile with FILE_FLAG_NO_BUFFERING , i should pass the input buffer equal or multiples of the Harddisk SECTOR Size, For Example, if my HDD sector size is 4096 BYTES, i will have to give input Buffer size of writeFile as (4096, 2*4096, 3*4096) etc.,

To make the writeFile work for input buffer size of lesser value than sector size or an imperfect multiple of sector-size say(512, 2048 etc.,), you will have to open the file handle using FILE_ATTRIBUTE_NORMAL attribute of CreateFile Function.

Hope this helps.,

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Everytime you use WriteFile, Clear its Buffer.
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gssajith87 7-Mar-13 8:56am    
Thanks Desai.,
My question is why do i get an INVALID_PARAMETER = 87., Error when i call the writefile with correct parameters., and why does it not throw any error when i change the buffer size.,

Actually it is very very simple...
All Writes must be Sector sized.
4096 byte sector needs a 4096 byte buffer - and a 512 byte sector requires a 512 byte buffer to be written. It is truly as simple as that.

Which of course does cause problems but that is what happens when writting to the hardware directly.
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