SCREENSIZE()
 Queries the number of characters that can be displayed on a screen or window
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 Syntax

     SCREENSIZE(<lMode>) --> nScreenSize

     Warning!  Contains <lMode>, an additional optional parameter over
     and above CA-Clipper Tools.

 Argument

     <lMode>  If this parameter is designated as .T., then SCREENSIZE()
     returns the size of the physical screen; otherwise, it returns the size
     of the selected window.  The default (.F.) is the selected window size.

 Returns

     SCREENSIZE() returns the number of bytes available for screen output, in
     an active window, or the physical screen.

 Description

     SCREENSIZE() determines the screen size memory in bytes.  With 25 lines
     and 80 columns, there are exactly 2000 characters.  For each character,
     there is also an attribute byte that results in 4000 bytes of screen
     memory.

     If SCREENSIZE() is called without parameters or with .F., it returns the
     active window size.  When called with .T., it returns the physical
     screen size.

 Example

     Display the number of available bytes:

     WOPEN(10, 10, 20, 70)      // Open a window
     ? SCREENSIZE()             // Size of window
     ? SCREENSIZE(.T.)          // Size of physical screen