Database Search

match allmatch any Look in all areasLook in current areas Check all datesPrevious dayPrevious 3 daysPrevious weekPrevious fortnightPrevious monthPrevious 2 monthsPrevious 3 monthsPrevious half-yearPrevious year

TechHome

• Build a Delimited Dir List for FileAppend File List
• Case Conversion Algorithm
• Change Old File and Path to New One
• Check File Date and Delete Older Files in Directory
• Check if File is Open or Exists
• Compare Directories
• Compute File Sizes
• Copy Files and Archive Attribute
• Copying Files from a Given Date
• Copying files XCOPY
• Count Keywords in Several Files
• Delete First Few Lines of a File
• Delete Temp Files Older Than
• Delimit a List of Files
• Display - Write File Contents to Screen
• Display Files in a Dialog with Case Sensitivity
• Fastest File Search Methods
• File Append for ASCII files with Ctrl-Zs in them
• File Counting and Item Counting Loop
• File List Sorted by Size
• File Mask Matching
• File or Item Extraction Loop
• FileCopy Error Handling
• FileOpen Error 1077 - Capture Additional Error Information
• FileVerInfo Constants
• FilVerInfo Returns Incorrect Version
• Get a List of Hidden Files in a Directory
• Get Date when File was Last Accessed Created Modified
• Get File Ownership in NT
• Get File Sizes Recursively
• Get Oldest or Newest File
• Get Users Home Directory
• Isolate Filename in a File Path
• List Files with Alternate Data Streams
• Merge Files with Binary Functions
• Parse Data from ASCII file using FileRead
• Progress Bar during FileCopy
• Read Part of File with BinaryRead
• Removing EOFs
• Renaming Files on an Incremental Basis
• Search for Upper Ascii Chars in File
• Sort a Flat File
• Tricky Bulk FileRename
• Write Various Quote Marks to Files

Can't find the information you are looking for here? Then leave a message over on our WinBatch Tech Support Forum.

How to Read Part of File with BinaryRead

Keywords: binaryread  dllcall

---

Question:

How do I read part of a file into a buffer?

Answer:

Starting in Winbatch 98A, see the function BinaryReadEx.

---

In earlier versions...There's no way to read just part of a file using the binary functions, but with the new DllCall() function you can do pretty much anything you want (having the Windows SDK documentation helps immensely). Here's an example:

  ;-------------------------------------------------------------------------

  file	  = FileLocate("winbatch.exe")
  ;
  ; "Requires Windows" string
  offset  = 67	; position from BOF/EOF to begin reading (0=first/last byte)
  direct  = 0	; direction to read (0=from beginning of file, 2=from end)
  bufsize = 40	; number of bytes to read
  ;
  ; Copyright notice near end of file
  ;offset  = 528
  ;direct  = 2
  ;bufsize = 41

  ;-------------------------------------------------------------------------

  If direct == 2 Then offset = -(Abs(offset))
  string = StrFill("", bufsize + 1)
  buffer = BinaryAlloc(bufsize + 1)
  hfile = FileOpen(file, "READ")
  dll = DllLoad("krnl386.exe")

  DllCall(dll, word:"_llseek", word:hfile, long:offset, word:direct)
  DllCall(dll, word:"_lread", word:hfile, lpbinary:buffer, word:bufsize)
  string = DllCall(dll, lpstr:"lstrcpy", lpstr:string, lpbinary:buffer)
  DllFree(dll)
  FileClose(hfile)
  BinaryFree(buffer)
  Message("String", string)

Note that the example above cannot be used to get a string which contains a NULL character, because the lstrcpy() function stops when it hits a NULL. I haven't found any way to get a DLL to modify a binary buffer, so I'm returning a string instead. If you need to get a block containing a NULL, you can do so by passing it from the DLL back to WinBatch via a temporary file, like this:

  ;-------------------------------------------------------------------------

  file	  = FileLocate("winbatch.exe")
  ;
  ; Chunk of text strings near end of file
  offset  = 708
  direct  = 2
  bufsize = 275

  ;-------------------------------------------------------------------------

  If direct == 2 Then offset = -(Abs(offset))

  tempfile = "tempfil$.tmp"
  buffer = BinaryAlloc(bufsize + 1)
  hfile = FileOpen(file, "READ")
  htemp = FileOpen(tempfile, "WRITE")
  dll = DllLoad("krnl386.exe")

  DllCall(dll, word:"_llseek", word:hfile, long:offset, word:direct)
  num = DllCall(dll, word:"_lread", word:hfile, lpbinary:buffer, word:bufsize)
  DllCall(dll, word:"_lwrite", word:htemp, lpbinary:buffer, word:num)
  DllFree(dll)
  
  FileClose(hfile)
  FileClose(htemp)
  BinaryRead(buffer, tempfile)
  FileDelete(tempfile)

  ; Now "buffer" contains the chunk of text.  Do what you want with it here.
  BinaryFree(buffer)

This seems a little kludgy, but it works nicely.

---

Article ID:   W13243

Filename:   Read Part of File with BinaryRead.txt

File Created: 2001:01:03:11:25:20

Last Updated: 2001:01:03:11:25:20