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Looking for a way to pre-allocate space in your WinAPI created file, don't wanna write a bunch of zeros? SetFileInformationByHandle looks promising for Vista+ but I never did get it working I did however find 'NtSetInformationFile' - Available starting with Windows 2000 ;hfile - handle to file opened with $GENERIC_WRITE access ;$llAllocationBytes - 64 bit int size to allocate for file __WinAPI_SetFileAllocationInfo($hFile, $llAllocationBytes) Func __WinAPI_SetFileAllocationInfo($hFile, $llAllocationBytes) Local Const $eFileAllocationInformation = 0x13 Local $t_FILE_ALLOCATION_INFO = DllStructCreate("Align 8;INT64") DllStructSetData($t_FILE_ALLOCATION_INFO, 1, $llAllocationBytes) Local $iRet = DllCall("ntdll.dll", "int", "NtSetInformationFile", _ "handle", $hFile, _ "int64*", 0, _ "ptr", DllStructGetPtr($t_FILE_ALLOCATION_INFO), _ "ulong", DllStructGetSize($t_FILE_ALLOCATION_INFO), _ "int", $eFileAllocationInformation) If @error Then Return False Return $iRet[0] = 0 EndFunc ;==>__WinAPI_SetFileAllocationInfo In case you are wondering (wandering?) here is my failed Attempt to call SetFileInformationByHandle more info: https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/ntifs/ns-ntifs-_file_allocation_information