Visual Basic for Applications Reference
Enables input/output (I/O) to a file.
Open pathname For mode [Access access] [lock] As [#]filenumber [Len=reclength]
The Open statement syntax has these parts:
|pathname||Required. String expression that specifies a file name may include directory or folder, and drive.|
|mode||Required. Keyword specifying the file mode: Append, Binary, Input, Output, or Random. If unspecified, the file is opened for Random access.|
|access||Optional. Keyword specifying the operations permitted on the open file: Read, Write, or Read Write.|
|lock||Optional. Keyword specifying the operations restricted on the open file by other processes: Shared, Lock Read, Lock Write, and Lock Read Write.|
|filenumber||Required. A valid file number in the range 1 to 511, inclusive. Use the FreeFile function to obtain the next available file number.|
|reclength||Optional. Number less than or equal to 32,767 (bytes). For files opened for random access, this value is the record length. For sequential files, this value is the number of characters buffered.|
You must open a file before any I/O operation can be performed on it. Open allocates a buffer for I/O to the file and determines the mode of access to use with the buffer.
Security Note When writing to files, an application may need to create a file if the file to which it is trying to write does not exist. To do so, it needs permission for the directory in which the file is to be created. However, if the file specified by FileName does exist, the application only needs Write permission to the file itself. Wherever possible, it is more secure to create the file during deployment and only grant Write permission to that file, rather than to the entire directory. It is also more secure to write data to user directories than to the root directory or the Program Files directory.
If the file specified by pathname doesn't exist, it is created when a file is opened for Append, Binary, Output, or Random modes.
If the file is already opened by another process and the specified type of access is not allowed, the Open operation fails and an error occurs.
The Len clause is ignored if mode is Binary.
Important In Binary, Input, and Random modes, you can open a file using a different file number without first closing the file. In Append and Output modes, you must close a file before opening it with a different file number.