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  • The lock was not performed
  • Locking a file
  • Position in the file
  • Operating mode in Windows Vista (and later)
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Stored procedures
Entirely or partially locks an external file. The file will be unlocked:
  • via fUnlock,
  • when the file is closed.
The application that locked the file can read this file and write into this file. The other applications cannot read this file or write into this file.
// Open an external file
FileID = fOpen("C:\MyDirectories\File.txt", foReadWrite)
IF FileID <> -1 THEN
...
// Lock the external file
ResLock = fLock(FileID)
...
END
Syntax
<Result> = fLock(<File identifier> [, <First byte to lock> [, <Number of bytes to lock>]])
<Result>: Boolean
  • True if the file was locked,
  • False otherwise.
<File identifier>: Integer
Identifier of the file to lock, defined by fOpen or fCreate.
<First byte to lock>: Optional integer
Position of the first byte to lock (0 corresponds to the first byte of the file).
<Number of bytes to lock>: Optional constant or integer
  • Number of bytes to lock in the file.
  • Constant:
    fLockEmptyFilefLock has the same behavior, no matter whether the file is empty or not (see the notes).
Remarks

The lock was not performed

fLock returns False if the file was not locked. The lock can be performed only if:
  • the external file is opened,
  • the file identifier is valid,
  • the file or the bytes to lock are not already locked by another computer or by another application.

Locking a file

  • The file is entirely locked if <First byte to lock> and <Number of bytes to lock> are not specified.
  • The file is locked from the first byte to lock (<First byte to lock>) until the end if <Number of bytes to lock> is not specified.
  • By default, fLock locks no byte if the file is empty. In this case, several applications can successfully "lock" an empty file. However, the file cannot be overwritten as long as the lock is performed.
To have the same behavior regardless whether the file is empty or not, use the fLockEmptyFile constant.
Linux The lock is effective between two different sites or contexts. Unlike Windows, a process cannot lock a file that was previouly locked.

Position in the file

When opening a file, the current position corresponds to:
  • the first byte of the file (by default),
  • the last file byte if the file is opened in "addition" mode (foAdd constant).
This position can be modified by fSeek.
The current position is not modified by the use of fLock.
WEBDEV - Server code

Operating mode in Windows Vista (and later)

If this function does not operate properly in Windows Vista (and later), check whether the file or directory used is not in one of the system directories (Windows directory or "Program Files" directory).
Indeed, in Windows Vista (and later), with the UAC mechanism (User Account Control) enabled, you must have the administrator privileges to handle and/or modify the files or directories in the system directories (Windows directory or "Program Files" directory).
Programming tip: To handle and/or modify the files or directories without administrator privileges, you should:
  • avoid writing into the Windows directory or into the "Program Files" directory,
  • use the system directory corresponding to the application (returned by SysDir associated with the srCommonAppData constant).
Related Examples:
Handling text files Unit examples (WINDEV): Handling text files
[ + ] Handling "text" files with WINDEV:
- Create a text file
- Write into a text file
- Read in a text file
Handling text files Unit examples (WEBDEV): Handling text files
[ + ] This example explains how to handle "non HFSQL" files with WEBDEV and it allows you to:
- Create a text file
- Write into a text file
- Read in a text file
Component : wd240std.dll
Minimum version required
  • Version 9
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