VB6 to VB.NET - Fixed length strings in structure

Question

I have an older vb app that creates a configuration structure with fixed length string arrays.  This structure is saved directly to disk and each file has exactly the same size and format.

VB.NET doesn't support fixed length strings or arrays.  How can I dimension my structure to emulate this and thus load the structure from pre-existing stored versions as the VB6 version does.

FileOpen(1, File, OpenMode.Random, , , Len(c))

How can I recreate this in the structure to be a fixed length structure so I can load and save exisitng structure data?

How do I recreate the functionallity of this statement?

Dim Param(7) As String * 8  ' Can't use

<VBFixedString(64),System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray,SizeConst:=64)> Public SpareS2() As Char ' "  - This doesn't work because it forces me to increase string size by 1 byte for the -1 value at the end.

 

 

 

 

Answer 1

Hi,

 

Structure Person
   Public ID As Integer
   Public MonthlySalary As Decimal
   Public LastReviewDate As Long
   <VBFixedString(15)> Public FirstName As String
   <VBFixedString(15)> Public LastName As String
   <VBFixedString(15)> Public Title As String
   <VBFixedString(150)> Public ReviewComments As String
End Structure

See also >>

http://msdn2.microsoft.com/fr-fr/library/aa903289(VS.71).aspx

 

Regards,

John

 

Answer 2

kaynos wrote:

I have an older vb app that creates a configuration structure with fixed length string arrays.  This structure is saved directly to disk and each file has exactly the same size and format. VB.NET doesn't support fixed length strings or arrays.  How can I dimension my structure to emulate this and thus load the structure from pre-existing stored versions as the VB6 version does. FileOpen(1, File, OpenMode.Random, , , Len(c)) How can I recreate this in the structure to be a fixed length structure so I can load and save exisitng structure data? How do I recreate the functionallity of this statement? Dim Param(7) As String * 8  ' Can't use <VBFixedString(64),System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray,SizeConst:=64)> Public SpareS2() As Char ' "  - This doesn't work because it forces me to increase string size by 1 byte for the -1 value at the end.

 

 

Hi,

 It does support fixed strings.

See my answer above.

Regards,

John

Answer 3

Spidermans_DarkSide wrote:

kaynos wrote: I have an older vb app that creates a configuration structure with fixed length string arrays.  This structure is saved directly to disk and each file has exactly the same size and format. VB.NET doesn't support fixed length strings or arrays.  How can I dimension my structure to emulate this and thus load the structure from pre-existing stored versions as the VB6 version does. FileOpen(1, File, OpenMode.Random, , , Len(c)) How can I recreate this in the structure to be a fixed length structure so I can load and save exisitng structure data? How do I recreate the functionallity of this statement? Dim Param(7) As String * 8  ' Can't use <VBFixedString(64),System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray,SizeConst:=64)> Public SpareS2() As Char ' "  - This doesn't work because it forces me to increase string size by 1 byte for the -1 value at the end.       Hi,  It does support fixed strings. See my answer above. Regards, S_DS

 

Ok..  So you are saying.  

<VBFixedString(20), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=21)> Public SepMeth() As Char

can be replaced by

<VBFixedString(20)> Public SepMeth() As Char

What are the functional differences, if any between the 2 statements?  the first was generated by the vb.net wizard when I opened the vb6 project in vs2005..

 

Secondly,  how can I create a fixed string array with a fixed number of elements..?  VB6 code was

Dim Param(7) As String * 8   '  I believe 8 array elements (starting at 0), 8 bytes long

Answer 4

 

 

Ok..  So you are saying.  

<VBFixedString(20), System.Runtime.InteropServices.MarshalAs(System.Runtime.InteropServices.UnmanagedType.ByValArray, SizeConst:=21)> Public SepMeth() As Char

can be replaced by

<VBFixedString(20)> Public SepMeth() As Char

What are the functional differences, if any between the 2 statements?  the first was generated by the vb.net wizard when I opened the vb6 project in vs2005..

 

Secondly,  how can I create a fixed string array with a fixed number of elements..?  VB6 code was

Dim Param(7) As String * 8   '  I believe 8 array elements (starting at 0), 8 bytes long

Hi kaynos,

 

Sorry I do not know the differences.

 

See this example structure for a VbFixedArray.>>

Public Structure ExampleStructure
  <VBFixedString(10)> Public myFixedString As String
  'Fixed arrays.>>
  <VBFixedArray(20)> Public myFixedOneDimensionalArray As Byte
  <VBFixedArray(30, 40)> Public myFixedTwoDimensionalArray As Char
End Structure

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Regards, John

Answer 5

Secondly,  how can I create a fixed string array with a fixed number of elements..?  VB6 code was

 

Dim Param(7) As String * 8   '  I believe 8 array elements (starting at 0), 8 bytes long

Public Structure Length8FixedString
  <VBFixedString(8)> Public myFixedString As String '8 is the STRING length.
End Structure

Public Structure ExampleStructure
  <VBFixedArray(7)> Public myArray As Length8FixedString '8 elements in this array at indexes 0,1,2,3,4,5,6,7
End Structure

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Regards, John

Answer 6

Hi ALL,

See also this thread which relates to the above for RANDOM FILE ACCESS.

>>

http://social.msdn.microsoft.com/Forums/en/vbgeneral/thread/50d7b930-edd3-4ba4-92fe-2c16e5235e51

 

Please note: This thread has recently ( about 2 hours ago ) had some or most of my posts marked as helpful,

by someone which is why I am replying now.    :-)    ;-)    :-D

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Regards,

John

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Answer 7

Hi John,

Have a question.. Why we need to have with fixed size string?

Can we use other datatypes as well like Int or Byte?

Answer 8

Hi John,

Have a question..

1) Why we need to have with fixed size string?

2) Can we use other datatypes as well like Int or Byte?

Hi Me.Saqib,

This thread of questions is quite old now and I have learned more stuff since February 2007 when this thread was started.  :-)

Referring to 1) above we do not have to have a fixed size string in everyday programming.

Fixed length strings are used when writing a record to a Random Access File

so that we know the length of each record in order to be able to access any record within the file.

See this thread for an example on random access file creation.>>

http://social.msdn.microsoft.com/Forums/en/vbgeneral/thread/50d7b930-edd3-4ba4-92fe-2c16e5235e51

 

2) Yes, of course you can also use other datatypes within a STRUCTURE or a CLASS.

 

The strings and arrays need to be of a fixed length though if you are doing

random access file programming as per my code here.>>

http://social.msdn.microsoft.com/Forums/en/vbgeneral/thread/50d7b930-edd3-4ba4-92fe-2c16e5235e51

 

I hope this helps.  :)    ;-)    :)    :-D

 

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Regards,

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Answer 9

Thanks John.

How would one differentiate b/w fixed length vs random access file?

Both same?