Write 2D array to a file - Xtreme Visual Basic Talk

11-08-2003, 10:32 AM

Dolptrmn

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Write 2D array to a file

I need a code which will write any 2D array of strings to a file (and code which will read it).
Is there a way to do it at all?

11-08-2003, 11:01 AM

Iceplug

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Yes. Assuming you already know how to write a file, you are going to need to find the bounds of the two dimensions with the UBound and LBound functions.
UBound(arr, 1) finds the last number in the first dimension.
UBound(arr, 2) finds the last number in the second dimension.
You can then just set up two looping variables in two For loops that will go through this whole array.

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11-08-2003, 12:28 PM

passel

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For the price of some User Defined Type overhead, using a UDT can give
you some flexibility in reading and writing arrays and dynamic strings to
a file.

The UDT will store the dimensions of arrays, and the lengths of
dynamic strings as part of its structure. It will use that information to
dynamically resize the arrays and strings when that information is read
back from a file.

So you can write the UDT in a single "put", and read back the UDT in a
single "get" from a file opened for binary input/output.

This example requires two command buttons.
The example defines a UDT to hold a dynamic array of dynamic strings.
This example will use one command button to declare a variable of this
type, and create a two dimensioned array of strings, and write the UDT
variable to a file opened for binary input/output.

The second button will then declare another variable of the UDT type.
It will open the file, and read the UDT into this variable.
The array and strings in the UDT will automatically be sized to hold the
information.
It will then loop through the dynamic array and print the strings to the
debug (immediate) window to show that it worked.

Code:

Private Type StringArrayType   'Define a User Defined Type (UDT)
  str() As String              'to hold a dynamic array of dynamic strings
End Type

Private Sub Command1_Click()
  Dim I As Integer, J As Integer
  Dim StrAry As StringArrayType  'Create a variable of the Dynamic string array type
  ReDim StrAry.str(1 To 3, 1 To 5)         'Make it a 3 x 5 array
  
  For I = 1 To 3                                        'For i = range of 1st dimension
    For J = 1 To 5                                      '  For j = range of 2nd dimension
      StrAry.str(I, J) = "I=" & str$(I) & ", J=" & str$(J)  'Store a string "I= i, J= j", 
    Next                                                    'where i = value of I and j = value of J
  Next
  Open "c:\tst.dat" For Binary As #1    'open a file for binary input/output
    Put #1, , StrAry                    '  Write the UDT variable to the file
  Close #1                              'Close the file
End Sub

Private Sub Command2_Click()
  Dim I As Integer, J As Integer
  Dim NewAry As StringArrayType         'Declare a variable of the dynamic string array type
  Open "c:\tst.dat" For Binary As #1    'Open the file
    Get #1, , NewAry                    '  Get the variable
  Close #1                              'Close the file
  For I = LBound(NewAry.str, 1) To UBound(NewAry.str, 1)
    For J = LBound(NewAry.str, 2) To UBound(NewAry.str, 2)
      Debug.Print NewAry.str(I, J)
    Next
  Next
End Sub

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11-08-2003, 12:43 PM

FireXtol

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A note about saving UDT's with passel's methods.

The original array which points to the UDT, must have it's bounds defined. It will not redimension it for you, and it'll error.

You can still use a dynamic array to point to the UDT. But make sure you redim the array to the number of UDT's first.

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11-08-2003, 07:42 PM

passel

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I wasn't proposing having an array of UDT's. I was proposing having a
single UDT which holds the array of strings. That way the array, being
part of the UDT, will be dimensioned automatically, as are the strings in
the array. My example saves and restores a two dimension array of
dynamic strings, contained in a single UDT.

As you noted, if you save an array, or strings outside of a UDT, then
you will have to know the dimensions of the array, or the lengths of the
strings, and pre-define them, in order for the "get" to return the proper
number of bytes to fill the array or strings.

Putting the array, and/or strings inside a UDT, allows Visual Basic to
keep track of the dimension of the arrays and the length of the strings.
Visual Basic will then dimension and fill the arrays and strings (in the
UDT) based on what was written to the file (for that UDT).

For an example of what FireXtol is talking about, I've modified the
example to use an array of UDTs. It's an array of 3 elements. Each
element (UDT) has a different sized 2 dimensional array of dynamic
strings in it (First element is 3x5, second element is 2x4, third element is
4x4). Since we are writing the array of UDTs to the file, we must
dimension the array (Dim NewAry(1 To 3) As StringArrayType) when we
want to read the array back from the file, because that information is
not saved in the file. But all the arrays, and strings within the UDTs are
restored properly, because the array dimensions and string sizes are
stored, in addition to the data, within the UDTs.

Here's the modified code.

Code:

Private Type StringArrayType   'Define a User Defined Type (UDT)
  str() As String              'to hold a dynamic array of dynamic strings
End Type

Private Sub Command1_Click()
  Dim I As Integer, J As Integer
  Dim StrAry(1 To 3) As StringArrayType  'Create a variable of the Dynamic string array type
  ReDim StrAry(1).str(1 To 3, 1 To 5)         'This element will contain a 3 x 5 array of strings
  ReDim StrAry(2).str(1 To 2, 1 To 4)         'This element will contain a 2 x 4 array of strings
  ReDim StrAry(3).str(1 To 4, 1 To 4)         'This element will contain a 4 x 4 array of strings
  
 'For each element in our array of 3 UDT's
 '  For whatever bounds our first dimension has
 '    For whatever bounds our second dimension has
 '      Set the String in the two dimensional array to a string identifying
 '          which UDT, 1st index and 2nd index of this string
 '    Next element in our second dimension
 '  next element in our first dimension
 'next UDT in our array of UDT's
  For k = 1 To 3
    For I = LBound(StrAry(k).str, 1) To UBound(StrAry(k).str, 1)     
      For J = LBound(StrAry(k).str, 2) To UBound(StrAry(k).str, 2)
        StrAry(k).str(I, J) = "UDT #" & str$(k) & ": I=" & str$(I) & ", J=" & str$(J)
      Next
    Next
  Next
  Open "c:\tst.dat" For Binary As #1    'open a file for binary input/output
    Put #1, , StrAry                    '  Write the array of UDTs to the file
  Close #1                              'Close the file
End Sub

Private Sub Command2_Click()
  Dim I As Integer, J As Integer
  Dim NewAry(1 To 3) As StringArrayType      'Declare an array of UDT's the same dimensions as was stored in the file
  Open "c:\tst.dat" For Binary As #1         'Open the file
    Get #1, , NewAry                         '  Get the array
  Close #1                                   'Close the file
 
 'For each element in our array of 3 UDT's
 '  For whatever bounds our first dimension has
 '    For whatever bounds our second dimension has
 '      Print the string in the UDT, defined by the two dimensional indexes
 '    Next element in our second dimension
 '  next element in our first dimension
 'next UDT in our array of UDT's
 For k = 1 To 3
  For I = LBound(NewAry(k).str, 1) To UBound(NewAry(k).str, 1)
    For J = LBound(NewAry(k).str, 2) To UBound(NewAry(k).str, 2)
      Debug.Print NewAry(k).str(I, J)
    Next
  Next
 Next
End Sub

Now this is a more complex situation than I usally deal with.
My original point was to use a single UDT to hold the two dimensioned
array of strings and do a single get or put to save and restore the
data.
But, as you can see here, even with this complexity (an array of UDTs,
with differing dimensioned arrays of strings), it still comes down to a
single Get or Put, to save or restore the data, you just need to keep
track of the size of the array yourself (you could put that information
into the file yourself, rather than hardcode it, but I'm not going to go
into how to do that. You would come up with a scheme to write and
read the additional information you need to the file).

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