GET (File I/O)
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 ]
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 ]
Usage:
Get #filenum, position, data [, [amount] [, bytesread ] ]
varres = Get (#filenum, position, data [, [amount] [, bytesread ] ] )
varres = Get (#filenum, position, data [, [amount] [, bytesread ] ] )
Parameters:
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.
dataIf position is omitted or zero (0), file reading will start from the current file position.
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 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 overwrite the pointer variable, not the memory it points to.
amountWhen 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 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 overwrite the pointer variable, not the memory it points to.
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.
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:
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:- 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.
- 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.
- It is also allowed in Input Access file mode, but this was never well tested and results may vary.
Examples:
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
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
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
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
' 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
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
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
- 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
- Put (File I/O)
- Open
- Close
- Binary
- Random
- Freefile
- File I/O methods comparison
Back to File I/O Functions
