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Your function uses the symbolic names for non-ASCII and special keys defined in the keys.h header file. These names are the same symbolic names as those used in the original library module.
The user terminates editing by pressing ENTER, ESCAPE, TAB, UP, DOWN, PGUP, PGDN or any of the function keys F(1) through F(12) inclusive. If the user presses ESCAPE, your function aborts editing, replaces the contents of the string with the original contents upon entry into your function, and leaves the offset and cursor position values unaltered. In order to be able to revert to the original string, your function needs to allocate memory at run time.
At termination, your function passes back through the same int variables the current values of the offset and the cursor position, unless no variables were pointed to upon entry into your function; that is, unless the value of either address was NULL.
*HOME - moves the cursor to the beginning of the string, changing the offset, if necessary.
*END - moves the cursor to the position to the right of the last character in the string, changing the offset, if necessary. If the last character is at the edge of the screen, moves the cursor to that character.
*INSERT - toggles Insert/Overstrike mode. In Insert mode, your function inserts a printable character into the string at the current cursor position, moves the remainder of the string to the right to make room for the inserted character, and positions the cursor just to the right of the inserted character. The printable characters are the characters from space (' ') to tilde ('~') inclusive in the ASCII table. In Overstrike mode, your function overwrites the character (if any) at the current cursor position with a printable character and advances the cursor just to the right of the new character. If the cursor is past the end of the string, your function appends a printable character to the string as long as the string isn't full, regardless of the mode.
*DEL - discards the character at the current cursor position and moves all characters to the right of the cursor position one position to the left.
