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Breaking the Textbox 64K File Size Limit (UPDATE: Sept. 15th, 2007)

Submitted on: 9/17/2007 8:47:26 AM
By: Tom Moran 
Level: Beginner
User Rating: By 11 Users
Compatibility: VB 5.0, VB 6.0
Views: 12160
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     You don't have to be limited to 64K size files for a for a standard Textbox control in VB6. This small sample project shows you how to load, edit and save plain text files, UNLIMITED by file size using the Standard VB6 Textbox control. It's all done in just a few simple lines of code. Please note that this method works on NT, Windows 2000, XP and Vista. If you're coding for systems that use Win95/98 or ME this method will not work. View the readhuge.txt file for full details. (UPDATE: Changed method from Clipboard method to an API method which is even more efficient and does not mess with any data in the clipboard and the end result is the same. Thanks to Kenneth Buckmaster and Rob C. for their input.)


Windows API/Global Declarations:

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'Windows API/Global Declarations for :Breaking the Textbox 64K File Size Limit (UPDATE: Sept. 15th, 2007)
'API's and Const to load large files
Private Declare Function SendMessage Lib "user32" _
 Alias "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, _
 ByVal wParam As Long, lParam As Any) As Long
Private Declare Function GetWindowTextLength Lib "user32" _
 Alias "GetWindowTextLengthA" (ByVal hwnd As Long) As Long
Private Const WM_SETTEXT = &HC
Private Const WM_GETTEXT = &HD
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9/10/2007 10:29:48 AMKenneth Buckmaster

Nice try but see MSDN EM_LIMITTEXT Message

"Edit controls on Windows 95/98/Me... For multiline edit controls, this value is either 0xFFFF bytes or the value of the wParam parameter, whichever is smaller."

So probably won't work with these os's
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9/10/2007 7:07:32 PMTom Moran

I have no idea if this works on Win95/98 or ME since I've only tested on XP and Vista should work for NT and 2000 as well. Would be interested if anyone out there is still using 95/98/ME to let me know.
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9/10/2007 7:22:47 PMRudyM

I didn't know you could do this either. I have XP and works fine. 5 Globes for discovering this trick. BTW, does anybody still use 95/98?
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9/11/2007 6:48:47 AMKasia Muniak

Kenneth Buckmaster is right.
It does not work in Win9x/Me.
The line:
frmHugeText.Text1.SelText = Clipboard.GetText()
caused error: '#7 - Out of memory.'
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9/11/2007 8:55:36 PMTom Moran

Ok then... this technique works only in NT, Windows 2000, XP and Vista. So if your programming for Win95/98/ME it's a no go. Still a pretty cool technique for those programming for this century.
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9/14/2007 4:04:42 AMRob C

5 Because you are correct.

I would encourage use of Option Explicit.
If you are placing code into BAS instead of FRM file, I would pass a reference to the Form as one of the arguments.
That is a 'cleaner' approach.

You mentioned that you would like to get rid of the RTB in one of your projects (which I applaud).
Did you ever do that ?
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9/14/2007 5:46:53 AMRob C

Your solution got me thinking, that there probably is an API call involved when pasting into the Textbox, and the API does not have the limit problem.
Did a 'Google' and came up with two solutions, both of which will not annoy the user by clearing what he previously had in the ClipBoard icles/ap200009.asp

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9/14/2007 9:42:08 PMTom Moran

Hey Rob: Thanks for the feedback. I was thinking the same thing as I was reading the MSDN article. I'm changing the example and am re-uploading. Re: Option Explicit... absolutely correct. Just threw the example together and forgot it. Thanks, again!
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9/18/2007 4:59:24 AMRobert Rayment

Very useful update. I have used RichTextBox for large files and, of course, you can color in etc. But the RTB has so many versions that it can be dodgy on some PCs.

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9/19/2007 2:33:40 AMTom Moran

You are correct, Robert. And there are times when you need to have plain ASCII text with no formatting. Even though you can save as text in a Rich Textbox, Windows still interprets the content as RTF. Guess that's why notepad is still alive and kicking. :)
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8/2/2008 11:34:21 PMKevin Ritch

Good submission.

5 Globes from me.

Kevin Ritch
PS - Groovy LOGO BTW.
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12/8/2008 4:00:09 AMRob C

Hi Tom,
It's me again.
I tripped over this today, and had another look at it.
I have enahnced the bas file to have no direct reference to the Form.
(IE there is no hard coding of the Form's name 'frmHugeText.').
Email me, if you would like me to send the project to you, at
robhp AT iprimus DOT com DOT au


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