Reading binary data in VB is really quite easy. I'm am providing some
example code here, with pointers to articles you might refer to in
case you want more examples or explainations.
Here, I will try to read a record ExampleData from a binary file.
Since you say that you already know the binary file record structure,
you can substitute my ExampleData structure with your own record
structure.
I have included code for both VB 6 & VB 7.NET
Explaination of code snippets : I try to read/write a fixed length
record from/to a binary file.The record contains a fixed length string
of 10 chars and an integer value. I first write one record of this
type to the file and then read one record from the file in binary
mode.I also show you how to get the length of an open file in VB.
CODE SNIPPETS FOR VB5/VB6
--------------------------
'Define ExampleData structure
Type Exampledata
Name as String * 10 'This is a fixed length string of 10
characters
Age as Integer
End Type
Dim myData As ExampleData ' Declare variable of type ExampleData
...
'Open Binary File
'FOr Binary Access, The Open function has the following format :
'Open filename For Binary As filenumber
Open "c:\BinaryFile.bin" For Binary As #1
'When writing to a binary file, we use the Put statement.
'Put #FileNumber, ByteNumber, VariableName
'ByteNumber is the file pos from which we start writing the data
Put #1,,myData ' Writes mydata in file at the current position
'Close the file
Close #1
....
'Read data from the file
Open "c:\BinaryFile.bin" For Binary As #1
'To read data, use the Get function
'Get #FileNumber, ByteNumber, VariableName
'Data is read from the binary file position specified by ByteNumber
Get #1,,myData 'Read in data from the current file pos
'Print Data
Debug.Print myData.Name
Debug.Print myData.Age
'To get the length of file, use the LOF(filenumber) function
Debug.Print "Length of the Binary File = " & LOF(1)
'Close File
Close #1
RELATED LINKS
-------------
- Binary Files - File Access by James Crowley
A very good tutorial On using Binary Files under VB. Highly
recommended!
( http://www.developerfusion.com/show/85/1/ )
- MSDN Help topic: "Using Binary File Access"
The standard MS Help Article on Binary files in VB 6
( http://msdn.microsoft.com/library/devprods/vs6/vbasic/vbcon98/vbconusingbinaryfileaccess.htm
)
- MS KnowledgeBase Q257794 - HOWTO: Use Binary File Access with
Visual Basic
Adds to the above MSDN Article. Provides example code for
variable length records access in a binary file using VB.
( http://support.microsoft.com/default.aspx?scid=KB;EN-US;Q257794&
)
- MS Support : File Access with Visual Basic® for Applications
Although for VBA, the same code works for VB6. Provides a list of
all the functions that can be used with the Binary file Access mode in
VB.Also provides example code.
( http://support.microsoft.com/default.aspx?scid=/support/excel/content/fileio/fileio.asp
)
======================
CODE SNIPPETS FOR VB7.NET
-------------------------
'Define ExampleData structure
Structure Exampledata
<VBFixedString(10)> Name as String 'Fixed length string of 10
characters
Age as Integer
End Type
Public myData As ExampleData ' Declare variable of type
ExampleData
...
'Open Binary File
'For Binary Access, use the FileOpen function which has the form :
'FileOpen(FileNumber, FileName, OpenMode.Binary)
FileOpen (1,"c:\BinaryFile.bin", OpenMode.Binary
'When writing to a binary file, we use the FilePut() function.
'FilePut( FileNumber,VariableName)
FilePut(1,myData) ' Writes mydata in file at the current position
'Close the file
FileClose(1)
....
'Read data from the file
FileOpen (1,"c:\BinaryFile.bin", OpenMode.Binary
'To read data, use the FileGet function
'FileGet (FileNumber, VariableName)
FileGet(1,myData) 'Read in data from the current file pos
'Display length of open file using the func. LOF(filenumber)
Debug.WriteLine(LOF(1))
'Close File
FileClose(1)
RELATED LINKS
-------------
- MSDN VB.NEt File Functions Reference
- FileOpen()
( http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vblr7/html/vastmopen.asp
)
- FilePut()
( http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vblr7/html/vastmput.asp
)
- FileGet()
( http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vblr7/html/vafctget.asp)
- LOF()
( http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vblr7/html/vafctlof.asp
)
MSDN Article : Binary File Access
( http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vbcn7/html/vaconopeningfileforbinaryaccess.asp
)
===========================
I hope the above answer will satisfy your needs.
If you need any clarifications, just ask.
Till the, Happy Coding !
:) |
Request for Answer Clarification by
watergeo-ga
on
02 Nov 2002 18:32 PST
The code structure is as follows. What I want to do is read the
header sections and tags and write those to another file. Then loop
through the data section modifying the values and writing them back
into a file with the same structure. I just still don't understand
how to read in values of a file without knowing exactly howlong the
variables are.
Here is the structure:
Surfer 7 grid files [.GRD] use a tag-based binary format to allow for
future enhancements. Each section is preceded by a tag structure,
which indicates the type and size of the following data. If a program
does not understand or want a particular type of data, it can read the
associated tag and quickly skip to the next section. In general,
sections can appear in any order except for the first, which must be a
Header section.
Data types used in Surfer 7 grid files:
Type Description
long 32 bit signed integer
double 64 bit double precision floating point value
Each section is preceded by a tag structure with the following format:
Element Type Description
Id long The type of data in the following section. See the next table
for a list of valid values.
Size long The number of bytes in the section (not including this tag).
Skipping this many bytes after reading the tag will align the file
pointer on the next tag.
Tag Id values. The 0x prefix indicates a hexadecimal value:
Id Description
0x42525344 Header section – must be the first section within the file.
0x44495247 Grid section – describes a 2D matrix of Z values.
0x41544144 Data section – contains a variable amount of data. The
size of the data section is given by the Size field in the tag
structure.
0x49544c46 Fault Info section – describes the fault traces used when
creating the grid.
The Header section must be the first section in the file and has the
following format:
Element Type Description
Version long Version number of the file format. Currently must be set
to 1.
The Grid section consists of a header that describes a 2D matrix of
values, followed by the matrix itself. This section encapsulates all
of the data that was traditionally referred to as a grid:
Element Type Description
nRow long number of rows in the grid
nCol long number of columns in the grid
xLL double X coordinate of the lower left corner of the grid
yLL double Y coordinate of the lower left corner of the grid
xSize double spacing between adjacent nodes in the X direction
(between columns)
ySize double spacing between adjacent nodes in the Y direction
(between rows)
zMin double minimum Z value within the grid
zMax double maximum Z value within the grid
Rotation double not currently used
BlankValue double nodes are blanked if greater or equal to this value
A Data section containing the 2D matrix of values must immediately
follow a Grid section. Within the Data section, the grid is stored in
row-major order, with the lowest row (minimum Y) first
A Fault Info section describes the fault geometry used to create the
grid. Fault Info sections have the following format:
Element Type Description
nTraces long number of fault traces (polylines)
nVertices long total number of vertices in all the traces
data section variable-sized data block consisting of an array of
Trace structures immediately followed by the array of vertices
A Data section containing an array of Trace structures and an array of
Vertex structures must immediately follow a Fault Info section. The
number of Trace structures in the array is nTraces, and the number of
Vertex structures is nVertices.
Trace structure:
Element Type Description
iFirst long 0-based index into the vertex array for the first vertex
of this trace
nPts long number of vertices in this trace
Vertex structure:
Element Type Description
x double X coordinate of the vertex
y double Y coordinate of the vertex
Example
The following example illustrates the layout for a 5 row by 10 column
grid:
Element Type Description
0x42525344 long Tag: Id for Header section
4 long Tag: Size of Header section
1 long Header Section: Version
0x44495247 long Tag: ID indicating a grid section
72 long Tag: Length in bytes of the grid section
5 long Grid Section: nRow
10 long Grid Section: nCol
0.0 double Grid Section: xLL
0.0 double Grid Section: yLL
1.0 double Grid Section: xSize
1.75 double Grid Section: ySize
25.0 double Grid Section: zMin
101.6 double Grid Section: zMax
0.0 double Grid Section: Rotation
1.70141e38 double Grid Section: BlankValue
0x41544144 long Tag: ID indicating a data section
400 long Tag: Length in bytes of the data section (5 rows x 10
columns x 8 bytes per double)
Z11, Z12, … double Data Section: First (lowest) row of matrix. 10
doubles
Z21, Z22, … double Data Section: Second row of matrix. 10 doubles
Z31, Z32, … double Data Section: Third row of matrix. 10 doubles
Z41, Z42, … double Data Section: Fourth row of matrix. 10 doubles
Z51, Z52, … double Data Section: Fifth row of matrix. 10 doubles
|
Clarification of Answer by
theta-ga
on
03 Nov 2002 12:09 PST
Silly Me! In my hurry, I posted my clarification as a Comment!
Well here it is again...
================================
water-geo, I am a little short on time today and so will not be able
to give a very in-depth tutorial on this matter, but i hope to make
the basics clear enough for you to solve this problem on your own. If
you still need any clarifications, i will gladly help you tomorrow.
BTW : Please specify which version of VB you are working with, in the
following example i assume you are using VB6.
-----------
First of all here are the VB6 data types you use :
Data Type VB6 Data Type VB7.NET Data types
32 bit Integer - Long - Integer
64 bit double - Double - Double
Id Description : To represent a hexadecimal value in VB6, you replace
the '0x' with '&H'. So the value 0x42525344 will be represented in VB6
as &H42525344
Ok, so you can create your header element like this :
Const HEADER_ID as Long = &H42525344
Type ElementHeader
Id as Long
Size as Long
Version as Long
End Type
dim Header as ElementHeader
'Open the file as shown in the answer
'While not End of file
'Read Header element as it must be the first
Get 1,,Header
if header.Id <> HEADER_ID then
' ERROR! First element in file is not Header Element
end if
'Close File
I hope this helped you get the idea. I am currently generating this
code off the top of my head so please forgive any syntax errors i
make.
Now to read the Data Grid :
You can define & read a grid element easily, it is a fixed length
record and the method to read it is the same as what is shown in case
of the HeaderElement.
Type ElementGrid
Id as...
Size as ...
nRow as Long
nCol as Long
<other variables>....
End Type
Dim Grid as ElementGrid
'Now read it just like we read the Header element
Now to read the Data Element
We define the Data Element as follows :
Option Base 1 'Now all out array indexes will start from 1 not 0.
Type ElementData
ID .....
Size ......
matrix() as Double
End Type
Dim Data as ElementData
'Open file , read header, grid
'After reading grid, we know the size of the data matrix
' Set the size of the matrix using the Redim() function
ReDim Data.matrix (Grid.nRow,nCol)
'Now read in the arrays
Get 1,,Data ' Simple wasnt it?
'Close file
So you can change the size of arrays dynamically using the ReDim
function.
You can use the same method for the FaultInfo section.
Here's a link to a VB6 Array tutorial
- Basics of Arrays by Robert Klieger
( http://www.geocities.com/alpha_productions2/vb_arrays.htm#Dynaming
)
Check out the dynamic arrays section
- MSDN ReDim() Reference
( http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vblr7/html/vastmReDim.asp
)
Also if you have the MSDN library installed, check it out.
Whoops! Gotta go!
Try out the above techniques and tell me how it goes.
Happy Coding!
:)
|
