Random

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Random

Opens a file with Open for reading and writing fixed-size records, 128 bytes by default.

Syntax

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

Parameters

• filename
• access_type
• lock_type
• filenum
• record_length

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:

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

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.

See also

• Open
• Binary
• Get #
• Put #

Examples

'' 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

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Category: File I/O Functions
Kind: keyword

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Reproduced from the FreeBASIC Wiki Manual under the GNU Free Documentation License 1.3 — with no Invariant Sections, no Front-Cover Texts and no Back-Cover Texts. Copyright © the FreeBASIC project and wiki contributors. See License.