curs_termcap(3X) curs_termcap(3X)
NAME
PC, UP, BC, ospeed, tgetent, tgetflag, tgetnum, tgetstr, tgoto, tputs -
direct curses interface to the terminfo capability database
SYNOPSIS
#include <curses.h>
#include <term.h>
extern char PC;
extern char * UP;
extern char * BC;
extern short ospeed;
int tgetent(char *bp, const char *name);
int tgetflag(const char *id);
int tgetnum(const char *id);
char *tgetstr(const char *id, char **area);
char *tgoto(const char *cap, int col, int row);
int tputs(const char *str, int affcnt, int (*putc)(int));)(int));
DESCRIPTION
These routines are included as a conversion aid for programs that use
the termcap library. Their parameters are the same and the routines
are emulated using the terminfo database. Thus, they can only be used
to query the capabilities of entries for which a terminfo entry has
been compiled.
INITIALIZATION
The tgetent routine loads the entry for name. It returns:
1 on success,
0 if there is no such entry (or that it is a generic type, having
too little information for curses applications to run), and
-1 if the terminfo database could not be found.
This differs from the termcap library in two ways:
• The emulation ignores the buffer pointer bp. The termcap
library would store a copy of the terminal description in the
area referenced by this pointer. However, ncurses stores its
terminal descriptions in compiled binary form, which is not the
same thing.
• There is a difference in return codes. The termcap library does
not check if the terminal description is marked with the generic
capability, or if the terminal description has cursor-
addressing.
CAPABILITY VALUES
The tgetflag routine gets the boolean entry for id, or zero if it is
not available.
The tgetnum routine gets the numeric entry for id, or -1 if it is not
available.
The tgetstr routine returns the string entry for id, or zero if it is
not available. Use tputs to output the returned string. The area
parameter is used as follows:
• It is assumed to be the address of a pointer to a buffer managed
by the calling application.
• However, ncurses checks to ensure that area is not NULL, and
also that the resulting buffer pointer is not NULL. If either
check fails, the area parameter is ignored.
• If the checks succeed, ncurses also copies the return value to
the buffer pointed to by area, and the area value will be
updated to point past the null ending this value.
• The return value itself is an address in the terminal
description which is loaded into memory.
Only the first two characters of the id parameter of tgetflag, tgetnum
and tgetstr are compared in lookups.
FORMATTING CAPABILITIES
The tgoto routine expands the given capability using the parameters.
• Because the capability may have padding characters, the output of
tgoto should be passed to tputs rather than some other output
function such as printf.
• While tgoto is assumed to be used for the two-parameter cursor
positioning capability, termcap applications also use it for
single-parameter capabilities.
Doing this shows a quirk in tgoto: most hardware terminals use
cursor addressing with row first, but the original developers of
the termcap interface chose to put the column parameter first. The
tgoto function swaps the order of parameters. It does this also
for calls requiring only a single parameter. In that case, the
first parameter is merely a placeholder.
• Normally the ncurses library is compiled with terminfo support. In
that case, tgoto uses tparm(3X) (a more capable formatter).
However, tparm is not a termcap feature, and portable termcap
applications should not rely upon its availability.
The tputs routine is described on the curs_terminfo(3X) manual page.
It can retrieve capabilities by either termcap or terminfo name.
GLOBAL VARIABLES
The variables PC, UP and BC are set by tgetent to the terminfo entry's
data for pad_char, cursor_up and backspace_if_not_bs, respectively. UP
is not used by ncurses. PC is used in the tdelay_output function. BC
is used in the tgoto emulation. The variable ospeed is set by ncurses
in a system-specific coding to reflect the terminal speed.
RETURN VALUE
Except where explicitly noted, routines that return an integer return
ERR upon failure and OK (SVr4 only specifies "an integer value other
than ERR") upon successful completion.
Routines that return pointers return NULL on error.
BUGS
If you call tgetstr to fetch ca or any other parameterized string, be
aware that it will be returned in terminfo notation, not the older and
not-quite-compatible termcap notation. This will not cause problems if
all you do with it is call tgoto or tparm, which both expand terminfo-
style strings as terminfo. (The tgoto function, if configured to
support termcap, will check if the string is indeed terminfo-style by
looking for "%p" parameters or "$<..>" delays, and invoke a termcap-
style parser if the string does not appear to be terminfo).
Because terminfo conventions for representing padding in string
capabilities differ from termcap's, tputs("50"); will put out a literal
"50" rather than busy-waiting for 50 milliseconds. Cope with it.
Note that termcap has nothing analogous to terminfo's sgr string. One
consequence of this is that termcap applications assume me (terminfo
sgr0) does not reset the alternate character set. This implementation
checks for, and modifies the data shown to the termcap interface to
accommodate termcap's limitation in this respect.
PORTABILITY
These functions are provided for supporting legacy applications, and
should not be used in new programs:
• The XSI Curses standard, Issue 4 describes these functions.
However, they are marked TO BE WITHDRAWN and may be removed in
future versions.
• X/Open Curses, Issue 5 (December 2007) marked the termcap interface
(along with vwprintw and vwscanw) as withdrawn.
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.
The comment that only the first two characters of the id parameter are
used escapes many application developers. The original BSD 4.2 termcap
library (and historical relics thereof) did not require a trailing null
NUL on the parameter name passed to tgetstr, tgetnum and tgetflag.
Some applications assume that the termcap interface does not require
the trailing NUL for the parameter name. Taking into account these
issues:
• As a special case, tgetflag matched against a single-character
identifier provided that was at the end of the terminal
description. You should not rely upon this behavior in portable
programs. This implementation disallows matches against single-
character capability names.
• This implementation disallows matches by the termcap interface
against extended capability names which are longer than two
characters.
SEE ALSO
curses(3X), terminfo(5), term_variables(3X), putc(3).
https://invisible-island.net/ncurses/tctest.html
curs_termcap(3X)
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