REQ: Declaring variables and file for random access

[Stefanie]

Hi,

I have a question about declaring variables for writing data to a file for
random access.
I have two string variables declared in a module (user-defined types).
The point is that for one of them i can't define (hard coded) a fixed
length because the application is reading data
from another file (In that file they have the same lenght).
Is it possible to use the lenght i obtain from reading that other file to
declare my variable or are there
other possibilities.

Thanks in advance,

Stefanie

[Martin Trump]

In message <15************ **************@ news1.zonnet.nl >, Stefanie
<St******@zsmai l.net> writes

file they have the same lenght). Is it possible to use the lenght i obtain from
reading that other file to
declare my variable or are there
other possibilities.

Off the top of my head. You can define a dynamic array within a user
defined type:-

Type mytype
....
mystring()
...
End Type

You can then set the size of mytype.mystring using:-

Redim mytype.mystring (Len(inputstrin g))

However, you may be storing up trouble if you want to use random access
on the resulting file. Where do you seek to for a new record?
HTH.

Regards

--
Martin Trump

[Steve Gerrard]

"Stefanie" <St******@zsmai l.net> wrote in message
news:15******** *************** ***@news1.zonne t.nl...
| Hi,
|
| I have a question about declaring variables for writing data to a file
for
| random access.
| I have two string variables declared in a module (user-defined types).
| The point is that for one of them i can't define (hard coded) a fixed
| length because the application is reading data
| from another file (In that file they have the same lenght).
| Is it possible to use the lenght i obtain from reading that other file
to
| declare my variable or are there
| other possibilities.
|
| Thanks in advance,
|
| Stefanie
|

I think what you are after is how to write a string to an output file
with a specified field width, without using a fixed length string, since
you don't know the fixed length needed until run time.

If so, then you should be able to do something like this:
n = FixedLengthNeed ed
j = Len(StringToWri te)

k = n - j ' spaces needed

If k > 0 Then
' print string and pad with spaces
Print #FileNum, StringToWrite, Space$(k)
Else
' clip string to maximum length
Print #FileNum, Left$(StringToW rite, n)
End If

[Stefanie]

Steve,

Thats the same as writing data to the file using Put, right ?

Stefanie

[J French]

On Mon, 6 Dec 2004 11:49:27 +0100, "Stefanie" <St******@zsmai l.net>
wrote:

Steve,

Thats the same as writing data to the file using Put, right ?

I could not see your first post

Below is a demo of Random Access using UDTs containing variable length
strings - the Record Length that it is opened with has to be large
enough.
- I would not do it like this personally

Option Explicit

Private Type TRec
L As Long
S As String
I As Integer
End Type

Private Sub Command1_Click( )
Dim Rec As TRec, Channel%

Rec.L = -1
Rec.S = "Test String"
Rec.I = -1

Channel = FreeFile
Open App.Path + "\test.dat" For Random As Channel Len = 200
Put #Channel, 1, Rec
Close #Channel

End Sub

Private Sub Command2_Click( )
Dim Rec As TRec, Channel%

Channel = FreeFile
Open App.Path + "\test.dat" For Random As Channel Len = 200
Get #Channel, 1, Rec
Close #Channel
Me.Print Rec.L, Rec.S, Rec.I

End Sub

[Steve Gerrard]

"Stefanie" <St******@zsmai l.net> wrote in message
news:38******** *************** ****@news1.zonn et.nl...
| Steve,
|
| Thats the same as writing data to the file using Put, right ?
|
| Stefanie
|

I'm hoping you have access to help files and can look up Put. Its
behavior with variable length strings varies according to whether they
are in a UDT, and whether the file is opened Random or Binary.

As far as I can tell, Put will write a 2 byte length before writing a
variable length string to a file opened Random (UDT or not), which
allows Get to retrieve it correctly. The total record length would have
to be long enough for that. I don't believe you actually have to pad out
the string length unless you want to.

[Randy Birch]

Interesting! I tried something similar yesterday, and got a 'bad record
length error when trying to do the Put.

--
Randy Birch
MS MVP Visual Basic
http://vbnet.mvps.org/
"J French" <er*****@nowher e.uk> wrote in message
news:41******** *******@news.bt click.com...
: On Mon, 6 Dec 2004 11:49:27 +0100, "Stefanie" <St******@zsmai l.net>
: wrote:
:
: >Steve,
: >
: >Thats the same as writing data to the file using Put, right ?
: >
:
: I could not see your first post
:
: Below is a demo of Random Access using UDTs containing variable length
: strings - the Record Length that it is opened with has to be large
: enough.
: - I would not do it like this personally
:
: Option Explicit
:
: Private Type TRec
: L As Long
: S As String
: I As Integer
: End Type
:
: Private Sub Command1_Click( )
: Dim Rec As TRec, Channel%
:
: Rec.L = -1
: Rec.S = "Test String"
: Rec.I = -1
:
: Channel = FreeFile
: Open App.Path + "\test.dat" For Random As Channel Len = 200
: Put #Channel, 1, Rec
: Close #Channel
:
: End Sub
:
: Private Sub Command2_Click( )
: Dim Rec As TRec, Channel%
:
: Channel = FreeFile
: Open App.Path + "\test.dat" For Random As Channel Len = 200
: Get #Channel, 1, Rec
: Close #Channel
: Me.Print Rec.L, Rec.S, Rec.I
:
: End Sub
:

[J French]

On Mon, 6 Dec 2004 22:36:52 -0500, "Randy Birch"
<rg************ @mvps.org> wrote:

Interesting! I tried something similar yesterday, and got a 'bad record
length error when trying to do the Put.

Yes, it will fail if the data is wider than the 'record length'
- something that needs to be manually checked

Personally I would be /very/ wary of using it

IMO data written to disk should be 'language independent'

[Stefanie]

Steve,

As far as I can tell, Put will write a 2 byte length before writing a
variable length string to a file opened Random (UDT or not), which
allows Get to retrieve it correctly. The total record length would have
to be long enough for that. I don't believe you actually have to pad out
the string length unless you want to.

Yes i read that too, but i don't understand how to do this:

This are the variables declared in my module.

Type Record
vDateTime As String * 19
vFileName As String
End Type

Public RecVar As Record

Using vFileName As String * 255 gives my enough for een full path, but most
of the time it's wasting space.

I use this for opening my file:

Open strFileName For Random As #Dnr Len = Len(RecVar)

But it's gives an error. "Bad record lenght"

Maybe somebody can offer me an example how to use the aforesaid.

Stefanie

[J French]

On Thu, 9 Dec 2004 12:38:00 +0100, "Stefanie" <St******@zsmai l.net>
wrote:

Steve,

As far as I can tell, Put will write a 2 byte length before writing a
variable length string to a file opened Random (UDT or not), which
allows Get to retrieve it correctly. The total record length would have
to be long enough for that. I don't believe you actually have to pad out
the string length unless you want to.

Yes i read that too, but i don't understand how to do this:

This are the variables declared in my module.

Type Record
vDateTime As String * 19
vFileName As String
End Type

Public RecVar As Record

Using vFileName As String * 255 gives my enough for een full path, but most
of the time it's wasting space.

I use this for opening my file:

Open strFileName For Random As #Dnr Len = Len(RecVar)

But it's gives an error. "Bad record lenght"

Maybe somebody can offer me an example how to use the aforesaid.

Look at the example I posted earlier in this thread

If you are interested in not wasting space then look carefully at
opening the file in Binary mode rather than Random mode

Have a careful look at the Seek Statement, and more importantly the
Seek Function.