API's for File Read

[sripriyaunni]

Please give me the API's by which I can read files in VB.
I am reading files with as many as 10000 records using VB Open method and the performance is very very poor.Please suggest ways of improving the performance of my application

[DSJ]

I like using the FileSystemObject (in Windows Scripting Runtime - SCRRUN.DLL) to read/write files, but I'm not sure how performance compares to the statements you're using. Let me know what you find out.

DJ

[Iouri]

Declare Function ReadFile Lib "kernel32.dll" (ByVal hFile As Long, lpBuffer As Any, _
ByVal nNumberOfBytesToRead As Long, lpNumberOfBytesRead As Long, lpOverlapped As Any) As Long

Description & Usage
ReadFile reads the desired amount of bytes from a file. The file must of course have been opened with at
least read-level access. If the file is synchronous (not overlapped), the function begins reading the file from
the current position of the file pointer, and the function automatically adjusts the file pointer to point to the
byte immediately after the last byte read. If the file is asynchronous (overlapped), the structure passed as
lpOverlapped identifies the point to begin reading from, and the program calling the function is responsible for
updating the file pointer.

Return Value
If an error occured, the function returns 0 (use GetLastError to get the error code).
If successful (including if the function attempted to read past the end of the file), the function returns a non-zero value.

Parameters

hFile
A handle to the file to read from. The file must have at least read-level access.
lpBuffer
The variable, array, or structure which receives the data read from the file.
nNumberOfBytesToRead
The number of bytes of data to read from the file and put into lpBuffer.
lpNumberOfBytesRead
Receives the number of bytes of data actually read from the file. If this is less than lpNumberOfBytesToRead, the function has attempted to read beyond the end of the file.
lpOverlapped
If the file is asynchronous (overlapped), this is an OVERLAPPED structure specifying where to begin reading from. If the file is synchronous (not overlapped), this must be 0.

Example

' Read both a Long (32-bit) number and a String from the file
' C:\Test\myfile.txt. Notice how the ByVal keyword must be used
' when reading a string variable.
Dim longbuffer As Long ' receives long read from file
Dim stringbuffer As String ' receives string read from file
Dim numread As Long ' receives number of bytes read from file
Dim hFile As Long ' handle of the open file
Dim retval As Long ' return value

' Open the file for read-level access.
hFile = CreateFile("C:\Test\myfile.txt", GENERAL_READ, FILE_SHARE_READ, ByVal CLng(0), OPEN_EXISTING, FILE_ATTRIBUTE_ARCHIVE, 0)
If hfile = -1 Then ' the file could not be opened
Debug.Print "Unable to open the file -- it probably does not exist."
End ' abort the program
End If

' Read a Long-type number from the file
retval = ReadFile(hFile, longbuffer, Len(longbuffer), numread, ByVal CLng(0))
If numread < Len(longbuffer) Then ' EOF reached
Debug.Print "End of file encountered -- could not read the data."
Else
Debug.Print "Number read from file:"; longbuffer
End If

' Read a 10-character string from the file
stringbuffer = Space(10) ' make room in the buffer
retval = ReadFile(hFile, ByVal stringbuffer, 10, numread, ByVal CLng(0))
If numread = 0 Then ' EOF reached
Debug.Print "End of file encountered -- could not read any data."
ElseIf numread < 10 Then ' read between 0 and 10 bytes
Debug.Print "Incomplete string read: "; Left(stringbuffer, numread)
Else
Debug.Print "String read from file: "; stringbuffer
End If

' Close the file.
retval = CloseHandle(hFile)


Iouri Boutchkine
iouri@hotsheet.com