Limits of Edit Controls
Edit controls were designed to enter, display, and edit small amounts of text. They were not meant to be the basis for large-scale text editors. Edit controls in Microsoft® Windows™ have the following limits:
Single-line edit controls are limited to a maximum of 32K (32,767 bytes) of text and, of course, to a single line. By default, single-line edit controls are limited to 30,000 characters. An application can change this limit to a maximum of 32,767 characters with the EM_LIMITTEXT message described in "Edit Control Messages," later in this article.
Multiple-line edit controls are limited to a maximum of 64K (65,535 bytes) of text. Whether a multiple-line edit control is actually able to approach this limit is based on how the edit control uses memory. Techniques to control the way edit controls use memory are described in the next section, "Edit Controls and Memory." Multiple-line edit controls are also limited to the following:
characters per line of text
lines of text
pixels per line of text