Member Avatar for ArchiMedes

Hi, I'm new around here & newish to VB 6.0 as well! :cheesy:

I'm using VB 6.0 to create a random access file, which has 2 fields per record . I know that all the records must be of equal length, but am wondering if there is a practical limit to the total number of bytes (or characters) that can be stored in a record of such a file.

If there is a maximum number here, what is it, please?

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Short answer and practical plan: VB6 random-access records must be fixed-length for Random mode, and the safe, usual approach is to use a user-defined Type with fixed-length strings (or fixed arrays) and then open the file with Len = Len(YourType). Variable-length strings and dynamic arrays introduce on-disk descriptors (extra bytes) and make the needed record length variable, so either avoid them inside the UDT or store them separately. (learn.microsoft.com)

A small, practical example for (two 140-char fields) — use fixed strings inside a Type, use Len(TypeVar) for the Open Len, and use Long for record numbers/positions:

Type Entry
  ID As Long
  English As String * 140
  Spanish As String * 140
End Type

Dim e As Entry
Dim fh As Integer
fh = FreeFile
Open App.Path & "\topic1.dat" For Random As #fh Len = Len(e)
' write record 1
e.ID = 1: e.English = "Hello": e.Spanish = "Hola"
Put #fh, 1, e
' read record 1
Get #fh, 1, e
Close #fh

Use NumRecords = LOF(fh) / Len(e) to compute how many records are in the file; trim trailing spaces on read (Trim$(e.English)) when presenting to users. These patterns follow the documented Random/Binary/Get rules and Len behavior. (learn.microsoft.com)

If you need dynamic arrays (asked by ), store them outside the fixed record or serialize them separately (Binary mode) — one simple trick is writing an array into a Variant and Put/Get that Variant to a binary file (write size/offsets or keep a small index in the main random file that points to the offset). Note: Get/Put add descriptors for variable strings and arrays (2 bytes for string length; arrays add descriptor bytes), so packing dynamic fields into Random-mode records is error-prone unless you explicitly account for those extra bytes. (learn.microsoft.com)

Troubleshooting tips: use Long (not Integer) for record indexes to avoid overflow errors; declare record length with Len() (or LenB() in byte-sensitive cases); test boundary sizes if you expect very large fields (many BASIC-era references warn of a practical ~32K boundary when variable-length descriptors are used); and if you need fast substring searches or lots of variable-length text, prefer Binary+index or a lightweight DB/ADO—random fixed records are best when fields are bounded and short. (stackoverflow.com)

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Member Avatar for Buff

Though I use PowerBasic for windows instead of VB, i'm sure the record
length for random files is quite large as it is with PB. Of course it should
be kept in mind that many times the larger the record, the more likely
wasted space is increased which is inherent in random (i.e. fixed length)
files especially when there are name. address. city, comment fields etc.

Member Avatar for ArchiMedes

Though I use PowerBasic for windows instead of VB, i'm sure the record
length for random files is quite large as it is with PB. Of course it should
be kept in mind that many times the larger the record, the more likely
wasted space is increased which is inherent in random (i.e. fixed length)
files especially when there are name. address. city, comment fields etc.

Thanks, Buff.

I've tried progressively increasing the record length, and VB 6.0 didn't complain! It will accept any value I'm likely to require, without hitting the ceiling, so I'm happy about that!

Agreed, random files can be quite wasteful on space. The two fields I've created each need to hold strings containing anything from 1 to 140 characters, so I'm compelled to set their lengths to the latter value. In an extreme case, a single ASCII character padded with 139 blanks would certainly not be economical!!

I don't know what alternatives exist to the use of random files, in order to save disc space. Sequential files are definitely out! I had wondered about binary files, but I read somewhere that these are generally used where the files are not going to be read by humans. To me this implies that there could be problems if I try to use them to store ordinary text.

Using a database is a possibility. VB 6.0 Pro version provides a form of database (Microsoft Access) ready built-in, but it appears to be a sawn-off version of the real thing. Have tried it out, but it will only allow me to search for a complete record. I have not persuaded it to look for a sub-string within a record. This is something that is very easy to do when my stuff is stored in one or more random files.

Ah well, I guess you pays your money & takes your choice! :)

Member Avatar for Buff

Thanks, Buff.

I had wondered about binary files, but I read somewhere that these are generally used where the files are not going to be read by humans. To me this implies that there could be problems if I try to use them to store ordinary text.

I don't know who wrote that but I would say they are full of ___t.
LOL.

Besides, you can treat any file as a binary file.In fact when you get right down to it, all files are binary files in one sense.

I would say that if the maximum length is only 140 then random files would be
good. That is a relatively small record size so the computer will read the records pretty fast and with today's large hard drives it would amount to only 14 Mb if you have 100,000 records.

Member Avatar for ArchiMedes

I would say that if the maximum length is only 140 then random files would be good. That is a relatively small record size so the computer will read the records pretty fast and with today's large hard drives it would amount to only 14 Mb if you have 100,000 records.

That's music to my ears, Buff. I shall stick to random files!

I'm writing a Spanish programme designed to assist English speakers to learn the language. The user can create any Topic he choses, (eg nouns, verbs, adjectives, notes of any description, extracts from a Spanish book, etc). For each Topic, a random file is created. Within a Topic, each Entry corresponds to a Record containing 2 string fields of 140 characters each, to hold respectively the English text & a corresponding Spanish version. ie, 280 characters per record.

It's impossible to predict how many Topics the user will create, or how many Entries he will place in each (depends upon how keen he is! :D ), but I envisage say, up to 100 such random files, with an average of 400 records in each. Anything in excess of that I would regard as exceptional!

Judging from what you say, although each record is 280 bytes, rather than the 140 I quoted previously, this level of usage should still scarcely make a dent on a large hard drive. (Specifically, 11.2 Mb, unless I've overlooked some other requirement). I guess there might be a problem with older machines where space is at a premium. That doesn't worry me unduly, 'cos I'm not distributing it for sale - just passing it on to a couple of unsuspecting family members!

The programme has various learning features, including a search facility & a test, with 10-50 randomly chosen questions, optionally against the clock, and a log file to which the test details, results & scores can be written. I have already got the programme up & running in QBasic, but I thought it would be fun & a challenge to create it again in Visual Basic, at which I am a raw beginner. It's proving to be an excellent way of learning Visual Basic. The more mistakes I make, the more I learn! It felt quite weird at first. In QBasic, you normally get the core code working first, then make the interface look pretty afterwards. With VB, it's the other way round. For me, that was the hardest part to swallow & took some getting used to! :eek: You've got to have at least a hazy idea of where you're going before you start to draw your user interface. At the time, seemed like trying to stick the wallpaper up first, then build the house afterwards.

Thanks for the help you've given me, Buff. I really appreciate it.

Member Avatar for ahmbil

Hello i will like to have an exemple to help me understand random access file(user define data type) using dynamic array in vb6.
Please with explanation.

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