Randomkeyword

Specifies file or device to be opened for random access mode

Syntax

Open filename for Random [Access access_type] [Lock lock_type] as [#]filenum [Len = record_length]

Parameters

Name		Description
`filename`		file name to open
`access_type`		indicates whether the file may be read from, written to or both
`lock_type`		locking to be used while the file is open
`filenum`		unused file number to associate with the open file
`record_length`		the size of the record used for the file

Description

Opens a file or device for reading and/or writing binary data in the given file filenum, with records of size record_length.
If the file does not exist, a new file will be created, otherwise any data existing in the file is preserved by Open. The file pointer is initialized by Open at the start of the file, at record number 1. File operations move the file position in steps of record_length bytes.
This file mode uses an user-defined Type buffer variable to read/write full records in a file. The buffer variable uses to include several fields.
The data is saved in binary mode, in the same internal format FreeBASIC uses, by means of Get # and Put #.

filename must be string expression resulting in a legal file name in the target OS, without wildcards. The file will be sought for in the present directory, unless a path is given.
Access_type - By default Random mode allows to both read and write the file, unless an Access type is specified, it must be one of:

Read - the file is opened for input only
Write - the file is opened for output only
Read Write - the file is opened for input and output (the default)

Lock_type indicates the way the file is locked for other processes (users or threads), it is one of:

Shared - The file can be freely accessed by other processes
Lock Read - The file can't be opened simultaneously for reading
Lock Write - The file can't be opened simultaneously for writing
Lock Read Write - The file cannot be opened simultaneously by other processes.

If no lock type is stated, the file will be Shared for other threads of the program and Lock Read Write for other programs.
Lock and Unlock can be used to restrict temporally access to parts of a file.

filenum is a valid FreeBASIC file number (in the range 1..255) not being used for any other file presently open. This number identifies the file for the rest of file operations. A free file number can be found using the FreeFile function.

record_length is the amount of bytes the file pointer will move for each individual Get and Put, it must match the size of the buffer variable used when Getting and Putting data. If omitted, it defaults to 128.

Remarks

Differences from QB

Care must be taken with dynamic or fixed length strings inside user defined types (UDT), see the warning at Type.
The keyword Field can only be used with Type to specify the packing of the UDT.

Example

'' This example generates a test file and then lets you view random records

'' that are read live from the file.



Type Entry

    slen As Byte

    sdata As String * 10

End Type



Dim u As Entry

Dim s As String



Open "testfile" For Random As #1 Len = SizeOf(Entry)



'' Write out 9 records with predefined data

For i As Integer = 1 To 9

    Read s

    u = Type( Len(s), s )

    Put #1, i, u

Next



Data ".,-?!'@:", "abc",      "def"

Data "ghi",      "jkl",      "mno"

Data "pqrs",     "tuv",      "wxyz"



'' Let the user view records by specifying their index number

Do

    Dim i As Integer

    Input "Record number: ", i

    If i < 1 Or i > 9 Then Exit Do



    Get #1, i, u

    Print i & ": " & Left( u.sdata, u.slen )

    Print

Loop



Close #1

Type ScoreEntry Field = 1

    As String * 20 Name

    As Single score

End Type



Dim As ScoreEntry entry



'' Generate a fake boring highscore file

Open "scores.dat" For Random Access Write As #1 Len = SizeOf(entry)

For i As Integer = 1 To 10

    entry.name = "Player " & i

    entry.score = i

    Put #1, i, entry

Next

Close #1



'' Read out and display the entries

Open "scores.dat" For Random Access Read As #1 Len = SizeOf(entry)

For i As Integer = 1 To 10

    Get #1, i, entry

    Print i & ":", entry.name, Str(entry.score), entry.score

Next

Close #1

Reference

Documented in KeyPgRandom.html