Get (File I/O)
Reads data from a file to a buffer
Get #filenum As Integer, [position As LongInt], ByRef data As Any [, [amount As Integer] [, ByRef bytesread As UInteger] ]
Get #filenum As Integer, [position As LongInt], data As String [, , ByRef bytesread As UInteger ]
Get #filenum As Integer, [position As LongInt], data() As Any [, , ByRef bytesread As UInteger ]
Get #filenum, position, data [, [amount] [, bytesread ] ]
varres = Get (#filenum, position, data [, [amount] [, bytesread ] ] )
filenum
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.
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.
Syntax
Get #filenum As Integer, [position As LongInt], ByRef data As Any [, [amount As Integer] [, ByRef bytesread As UInteger] ]
Get #filenum As Integer, [position As LongInt], data As String [, , ByRef bytesread As UInteger ]
Get #filenum As Integer, [position As LongInt], data() As Any [, , ByRef bytesread As UInteger ]
Usage
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.
positionThe 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 or a dereferenced pointer. The read operation will try to fill completely the variable, unless the EOF is reached.
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.
bytesreadAn unsigned integer variable to accept the result of the number of bytes read successfully from the file.
Return Value
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.
Example
Dim Shared f As Integer
Sub get_integer()
Dim buffer As Integer ' Integer variable
' Read an Integer (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 Integer ' array of Integers
' Read 10 Integers (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 Integer Ptr
' allocate memory for 5 Integers
pmem = Allocate(5 * SizeOf(Integer))
' Read 5 integers (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_integer()
get_array()
get_mem()
' Close the file.
Close #f
Sub get_integer()
Dim buffer As Integer ' Integer variable
' Read an Integer (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 Integer ' array of Integers
' Read 10 Integers (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 Integer Ptr
' allocate memory for 5 Integers
pmem = Allocate(5 * SizeOf(Integer))
' Read 5 integers (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_integer()
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
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
- Put (File I/O)
- Open
- Close
- Binary
- Random
- FreeFile
- File I/O methods comparison
