Get (File I/O)keyword

Reads data from a file to a buffer

Syntax

Get #filenum As Long, [position As LongInt], ByRef data As Any [, [amount As UInteger] [, ByRef bytesread As UInteger] ]

Get #filenum As Long, [position As LongInt], data As String [, , ByRef bytesread As UInteger ]

Get #filenum As Long, [position As LongInt], data() As Any [, , ByRef bytesread As UInteger ]

Parameters

Name		Description
`filenum`		The value passed to `Open` when the file was opened.
`position`		The position where the read must start. If the file was opened `For Random`, the position is in records; otherwise, it is in bytes. If omitted, reading starts at the present file pointer position. The position is 1-based: i.e. first record or byte of a file is at position `1`. If
`position`		is omitted or zero (`0`), file reading will start from the current file position.
`data`		The buffer where data is written. It can be a numeric variable, a string, an array, a user defined type (including referenced by `This`), or a dereferenced pointer. The read operation will try to fill completely the variable, unless the `EOF` is reached. For a user-defined type instance, the data impacted is only the non-static data members. When getting arrays,
`data`		should be followed by an empty pair of brackets: "`()`". `Get` will read data for all of the values in the array.
`amount`		is not allowed. When getting `String`s, the number of bytes read is the same as the number of bytes in the string data.
`amount`		is not allowed. Note: If you want to read values into a buffer, you should NOT pass a pointer to the buffer; instead you should pass the first variable in the buffer (this can be done by dereferencing the pointer with `Operator * (Value Of)`). If you pass a pointer directly, then `Get` will overwrite the pointer variable, not the memory it points to.
`amount`		Makes `Get` read
`amount`		consecutive variables from file to memory, i.e. it reads `(amount * SizeOf(data) )` bytes of data from file into the memory starting at
`data`		's memory location. If
`amount`		is omitted it defaults to `1`, meaning that `Get` just reads a single variable.
`bytesread`		An unsigned integer variable to accept the result of the number of bytes read successfully from the file.

Return value

Get() returns a 32 bit Long: a zero (0) on success; non-zero on error.
Note: if EOF (end of file) is reached while reading, Get will return success. The amount of bytes actually read can be checked by passing a bytesread variable.

Description

Reads binary data from a file to a buffer variable

Get can be used as a function, and will return 0 on success or an error code on failure.

For files opened in Random mode, the size in bytes of the data to read must match the specified record size.

Note:

- If a real [w/z]string variable is passed to Get, the amount parameter should be forbidden as it is when passing a string. Do not use. Otherwise, it is ignored (except for the '0' value).
- If a dereferenced [w/z]string pointer is passed to Get, the amount parameter is not taken into account as it is when passing a dereferenced numeric pointer. Do not use. But instead of respecting the amount parameter, the pointed buffer must begin with at least as many non-zero elements as the number of elements to read.
- For finer granularity, any [w/z]string variable can be safely passed to Get as a numeric buffer by providing the first numeric element (an indexed [w/z]string variable, or a dereferenced [w/z]string pointer then indexed) and the number of numeric elements to be processed.

Note:

- Using Get # is naturally dedicated to Binary/Random Access file mode.
- It is also allowed in Input Access file mode, but this was never well tested and results may vary.

Remarks

Usage



Get #filenum, position, data [, [amount] [, bytesread ] ]

varres = Get (#filenum, position, data [, [amount] [, bytesread ] ] )

Differences from QB

Get in FB can read full arrays as in VB or, alternatively, read a multiple of the data size into the memory.
Get can be used as a function in FB, to find the success/error code returned without having to use error handling procedures.
FB allows the bytesread parameter, to check how many bytes have been successfully read in.

Example

Dim Shared f As Integer



Sub get_long()



    Dim buffer As Long ' Long variable



    ' Read a Long (4 bytes) from the file into buffer, using file number "f".

    Get #f, , buffer



    ' print out result

    Print buffer

    Print



End Sub



Sub get_array()



    Dim an_array(0 To 10-1) As Long ' array of Longs



    ' Read 10 Longs (10 * 4 = 40 bytes) from the file into an_array, using file number "f".

    Get #f, , an_array()



    ' print out result

    For i As Integer = 0 To 10-1

        Print an_array(i)

    Next

    Print



End Sub



Sub get_mem



    Dim pmem As Long Ptr



    ' allocate memory for 5 Longs

    pmem = Allocate(5 * SizeOf(Long))



    ' Read 5 Longs (5 * 4 = 20 bytes) from the file into allocated memory

    Get #f, , *pmem, 5 ' Note pmem must be dereferenced (*pmem, or pmem[0])



    ' print out result using [] Pointer Indexing

    For i As Integer = 0 To 5-1

        Print pmem[i]

    Next

    Print



    ' free pointer memory to prevent memory leak

    Deallocate pmem



End Sub



' Find the first free file file number.

f = FreeFile



' Open the file "file.ext" for binary usage, using the file number "f".

Open "file.ext" For Binary As #f



  get_long()



  get_array()



  get_mem()



' Close the file.  

Close #f

' Load a small text file to a string



Function LoadFile(ByRef filename As String) As String

    

    Dim h As Integer

    Dim txt As String

    

    h = FreeFile

    

    If Open( filename For Binary Access Read As #h ) <> 0 Then Return ""

    

    If LOF(h) > 0 Then

        

        txt = String(LOF(h), 0)

        If Get( #h, ,txt ) <> 0 Then txt = ""

        

    End If

    

    Close #h

    

    Return txt

    

End Function



Dim ExampleStr As String

ExampleStr = LoadFile("smallfile.txt")

Print ExampleStr

' 'THIS' can be used as argument for writing/filling all non-static data of an UDT instance to/from a file



Type UDT

    Dim As String * 32 s

    Dim As Double d

    Declare Sub Save(ByRef filename As String)

    Declare Sub Load(ByRef filename As String)

End Type



Sub UDT.Save(ByRef filename As String)

    Dim As Integer f

    f = FreeFile()

    Open filename For Binary As #f

    Put #f, , This  '' writes all non-static data of the UDT instance to the file

    Close #f

End Sub



Sub UDT.Load(ByRef filename As String)

    Dim As Integer f

    f = FreeFile()

    Open filename For Binary As #f

    Get #f, , This  '' fills all non-static data of the UDT instance from the file

    Close #f

End Sub



Dim As UDT u1

u1.s = "PI number"

u1.d = 3.14159

u1.Save("file.ext")



Dim As UDT u2

u2.Load("file.ext")

Print u2.s

Print u2.d

Reference

Documented in KeyPgGetfileio.html