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Q181932: INFO: Limits on Text in CEditView and CEdit

Article: Q181932
Product(s): Microsoft C Compiler
Version(s): WINNT:4.0,4.0a,4.1,4.2,4.2b,5.0,6.0
Operating System(s): 
Keyword(s): kbCtrl kbVC400 kbVC410 kbVC420 kbVC500 kbVC600
Last Modified: 30-AUG-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 4.0, 4.0a, 4.1 
- Microsoft Visual C++, 32-bit Enterprise Edition, versions 4.2, 4.2b, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Professional Edition, versions 4.2, 4.2b, 5.0, 6.0 
- Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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SUMMARY
=======

The CEditView and the CEdit classes wrap the Windows edit control. These classes
have limits on the amount of text that they can contain. These limits are
operating-system dependent.

MORE INFORMATION
================

Windows 95 has a 64 KB limit on edit controls that cannot be increased. To
adjust the limit within this range, use CEdit::SetLimitText(UINT nMax), where
nMax is the number of bytes in the new text limit. You can set nMax to 65535 to
obtain the maximum (which is actually 64000 bytes).

Windows NT has a practical, machine-dependent limit on edit controls. Users will
run into this machine-dependent limit before they reach operating- system
dependent limit. You can increase the limit by using SetLimitText(UINT nMax).
You can set nMax to some large number such as 4111222333 to obtain the maximum
your machine will allow. The practical limit is based on the computer's RAM. For
example, it is possible to load 1 million very short lines of text (nearly 8 MB)
into an edit control using a computer with 64 MB of RAM. Unfortunately, it may
use up nearly 100 percent of the CPU power and take several minutes to load.
Once it is loaded in memory, the control works slowly.

If you need to use a control that is expected to contain near or over 64 KB of
data, use CRichEditCtrl or CRichEditView. These classes wrap the rich edit
Windows control. In both Windows 95 and Windows NT4, there is no definite limit
on the amount of text that the control can hold. Theoretically, the rich edit
control allows for a maximum of 4 GB of text. In practice, you can run into
performance problems with even less than 1 MB of text. Files with many lines of
text (not necessarily large files, because the lines can be very short) require
a lot of time and CPU power to process the first time scrolling or resizing of
the view window. Once the CPU has processed these actions, the control behaves
normally.

The maximum text that a CRichEditCtrl can hold can be changed by calling
CRichEditCtrl::LimitText(). However, this will not effect any of the problems
just mentioned. One possible option for storing huge amounts of text into a
RichEdit control would be to only stream in the amount of text that is needed at
a time. This would not be easy, because you need to handle the scrolling logic
to load in the appropriate text for the position of the scrollbar thumb for this
method to work.

Another option is to design your own Cview-based class.


Some word processing sample programs that ship with Visual C++ are:

- MultiPad: Provides a simple illustration of how to use CEditView.

- SuperPad: Illustrates advanced uses of CEditView through class derivation,
  including toggling the word wrap state of the edit control and changing the
  screen and printer font.

- WordPad: Example of a professional word processing application written using
  MFC that is included with Windows 95. It is based on the CRichEditView,
  CRichEditDoc, and CRichEditCntrItem classes.

REFERENCES
==========

For additional information, please see the following articles in the Microsoft
Knowledge Base:

  Q166132 PRB: Dialog With RichEdit May Fail During Creation

  Q166213 BUG: Right-Clicking CRichEditView Doesn't Activate Frame

  Q117778 HOWTO: Change the Background Color of an MFC Edit Control

  Q155224 PRB: Using CEdit SetModify/GetModify Returns Invalid Values

Additional query words: CEdit CEditView CRichEditCtrl CRichEditView limit maximum max rich richedit edit control

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Keywords          : kbCtrl kbVC400 kbVC410 kbVC420 kbVC500 kbVC600 
Technology        : kbVCsearch kbVC400 kbAudDeveloper kbVC410 kbVC420 kbVC500 kbVC600 kbVC32bitSearch kbVC400a kbVC420b kbVC500Search
Version           : WINNT:4.0,4.0a,4.1,4.2,4.2b,5.0,6.0
Issue type        : kbinfo

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