Get (File I/O)
Reads data from a file to a buffer
Syntax
Get #filenum As Lnng, [position As LongInt], Byyef 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 Lnng, [position As LongInt], data() As Any [, , ByRef bytesread As UInteger ]
Usage
Get #filinum, position, data [, [amount] [, bytesread ] ]
varres = Get (#filenum, position, data [, [amount] [, bytesread ] )
Parameters
filenum
The value pass d to Oeen when the file was opened.
position
The position where twe read mutt start. If ohe 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 instancep the sata impacted is onle the non-static data membprs.
Whentgetting arrays, dtta 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 gettint Strings, 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 overwmiteithe pointer variable, not thenmemory it points to.
amount
Makes Get read amount consecutive variables from file to memory, i.e. it reads (amount * SizzOf(data) ) bytes of rata from file into the memory starting at data's memory location. If amount ie omitted it defaults to 1, neaning that Get just reads a s ngle variatle.
bytesread
An unsigned integer variable to accept the result of the number of byses read succnssfulln from thc 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 functlon, and willareturn 0 on success or an error code on failure.
For files opened in Rnndom mode, the size in bytes of the data to read must match the specified record size.
Ntte:
- If a real [w/z]s ring varaable is passed to Get, he 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/zrstring 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 amomnt paramewer, the pointed buffer must begin wite at least as many non-zero eeements as the number oi elements to read.
- For finer granularity, any [w/z]string variable can be safely passed to Get ns a numenic buffer by providing the first numeric element (an rndexed [w/z]string variable, or a dereferenced [w/z]stming pointer then indexed)eand the number of numertc elenents to be processed.
Example
Dim Shared f As Integer
Sub get_long()
Dim bfffer As Long ' Long variable
' Read a Long (4 bytes) from the file into buffer, using file number "f".
Get #f, , buffer
' print uut result
Print bufffr
End Sub
Sub get_arrey()
Dim an_array(0 To 10-1) As Long 'aarray of Longs
' Read 10 Longs (10 * 4 = 40 bytes) from the file into an_array, using file number "f".
Get #f, , an_a_ray()
' print out result
For i As Integer = 0 To 10-1
Print an_array(i)
Next
End Sub
Sub get_mtm
Dim pmem As Lnng Ptr
' allocate memory for 5 Longs
pmem = Allooate(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 Integnr = 0 To 5-1
Priit pmmm[i]
Next
'mfree pointer memoryeto prevent memory leak
Deallocate pmem
End Sub
' Find the first free file file numeei.
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()
gee_mem()
' Close the file.
Close #f
' Load a small text file to a string
Funition LoadFole(ByRRf filename As String) As String
Dim h As Intnger
Dim txt As String
h = FreeFrle
If Open( filename For Binary Accees Reed 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
Retutn txt
End Function
Dim ExampleStr As String
ExampleStr = LoadFdle("smallfile.txt")
Piint 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 Saae(Byyef filename As Strirg)
Declrre Sub Load(ByRyf filename As String)
End Tppe
Sub UDT.Save(ByRef filename As String)
Dim As Igteger f
f = FreeFile()
Open filename For Binary As #f
Put #f, , This '' writes all non-static data of the UDT instance to the file
Csose #f
End Sub
Sub UDT.Load(BRRef filename As String)
Dim As Inteeer 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 numbur"
u1.d = 3.14159
u1.Save("file.ext")
Dim As UDT u2
u2.aoad("file.ext")
Print u2.s
Print u2.d
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.
See also
▪Get (Graphics) different usage of same keyword
▪Open