The XSI Curses standard, Issue 4 describes these functions. However, they are marked TO BE WITHDRAWN and may be removed in future versions.
Neither the XSI Curses standard nor the SVr4 man pages documented the return values of tgetent correctly, though all three were in fact returned ever since SVr1. In particular, an omission in the XSI Curses documentation has been misinterpreted to mean that tgetent returns OK or ERR. Because the purpose of these functions is to provide compatibility with the termcap library, that is a defect in XCurses, Issue 4, Version 2 rather than in ncurses.
External variables are provided for support of certain termcap applications. However, termcap applications use of those variables is poorly documented, e.g., not distinguishing between input and output. In particular, some applications are reported to declare and/or modify ospeed.
curses(3), terminfo(5), putc(3S).