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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | PORTABILITY | HISTORY | BUGS | SEE ALSO | COLOPHON |
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curs_termcap(3X) Library calls curs_termcap(3X)
PC, UP, BC, ospeed, tgetent, tgetflag, tgetnum, tgetstr, tgoto,
tputs - curses emulation of termcap
#include <curses.h>
#include <term.h>
char PC;
char * UP;
char * BC;
@NCURSES_OSPEED@ ospeed;
int tgetent(char * bp, const char * name);
int tgetflag(const char * id);
int tgetnum(const char * id);
char * tgetstr(const char * id, char ** sbuf);
char * tgoto(const char * cap, int col, int row);
int tputs(const char * str, int affcnt, int (* putc)(int));
ncurses provides the foregoing variables and functions as a
compatibility layer for programs that use the termcap library.
The API is the same, but behavior is emulated using the terminfo
database. Thus, it can be used only to query the capabilities of
terminal database entries for which a terminfo entry has been
compiled.
Initialization
tgetent loads the terminal database entry for name; see term(7).
This must be done before calling any of the other functions. It
returns
1 on success,
0 if there is no such entry (or if the matching entry
describes a generic terminal, having too little
information for curses applications to run), and
-1 if the terminfo database could not be found.
This implementation differs from those of historical termcap
libraries.
• ncurses ignores the buffer pointer bp, as do other termcap
implementations conforming to portions of X/Open Curses now
withdrawn. The BSD termcap library would store a copy of the
terminal type description in the buffer referenced by this
pointer. terminfo stores terminal type descriptions in
compiled form, which is not the same thing.
• The meanings of the return values differ. The BSD termcap
library does not check whether the terminal type description
includes the generic (gn) capability, nor whether the terminal
type description supports an addressable cursor, a property
essential for any curses implementation to operate.
Retrieving Capability Values
tgetflag reports the Boolean entry for id, or zero if it is not
available.
tgetnum obtains the numeric entry for id, or -1 if it is not
available.
tgetstr returns the string entry for id, or NULL if it is not
available. Use tputs to output the string returned. The sbuf
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 sbuf is not NULL, and
that the pointer obtained by dereferencing sbuf is also not
NULL. If either check fails, ncurses ignores sbuf.
• If the checks succeed, ncurses also copies the return value to
the buffer pointed to by sbuf, and the library updates sbuf to
point past the null character terminating this value.
• The return value itself is an address in the terminal type
description loaded into memory.
Applying String Capabilities
String capabilities can be parameterized; see subsection
“Parameterized Strings” in terminfo(5). tgoto applies its second
and third arguments to the parametric placeholders in the
capability stored in the first argument.
• The capability may contain padding specifications; see
subsection “Delays and Padding” of terminfo(5). The output of
tgoto should thus be passed to tputs rather than some other
output function such as printf(3).
• While tgoto is assumed to be used for the two-parameter cursor
positioning capability, termcap applications also use it for
single-parameter capabilities.
Doing so reveals 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 col (column)
parameter first. The tgoto function swaps the order of its
parameters. It does this even for calls requiring only a
single parameter. In that case, the first parameter is merely
a placeholder.
• Normally the ncurses library is compiled without full termcap
support. In that case, tgoto uses an internal version of
tparm(3X) (a more capable function).
Because it uses tparm internally, tgoto is able to use some
terminfo features, but not all. In particular, it allows only
numeric parameters; tparm supports string parameters.
However, tparm is not a termcap feature, and portable termcap
applications should not rely upon its availability.
tputs is described in curs_terminfo(3X). It can retrieve
capabilities by either termcap or terminfo code.
Global Variables
tgetent sets the variables PC, UP, and BC to the terminfo entry's
data for pad_char (pad), cursor_up (cuu1), and backspace_if_not_bs
(OTbs), respectively. ncurses does not employ cuu1 internally.
delay_output(3X) uses pad, while tgoto emulation uses the obsolete
termcap capability bs, represented in ncurses terminfo as “OTbs”.
ncurses assigns the variable ospeed a system-specific value to
encode the terminal's data rate.
Releasing Memory
The termcap functions provide no means of freeing memory, because
legacy termcap implementations used only the storage provided by
the caller via tgetent and tgetstr. Those buffers are unused in
terminfo.
By contrast, terminfo allocates memory. It uses setupterm(3X) to
obtain the data used by tgetent and the functions that retrieve
capability values. One could use
del_curterm(cur_term);
to free this memory, but there is an additional complication with
ncurses. It uses a fixed-size pool of storage locations, one per
value of the terminal name parameter given to tgetent. The
screen(1) program relies upon this arrangement to improve its
performance.
An application that uses only the termcap functions, not the
higher-level curses API, could release the memory using
del_curterm(3X), because the pool is freed using other functions;
see curs_memleaks(3X).
The return values of tgetent, tgetflag, tgetname, and tgetstr are
documented above.
tgoto returns NULL on error. Error conditions include:
• uninitialized state (tgetent was not called successfully),
• cap being a null pointer,
• cap referring to a canceled capability,
• cap being a capability with string-valued parameters (a term‐
info-only feature), and
• cap being a capability with more than two parameters.
See curs_terminfo(3X) regarding tputs.
ncurses compares only the first two characters of the id parameter
of tgetflag, tgetnum, and tgetstr to the capability names in the
database.
These functions are no longer standardized (and the variables
never were); see section “HISTORY” below. ncurses provides them
to support legacy applications; they should not be used in new
programs.
SVr4 describes a successful return value only as “an integer value
other than ERR”.
Neither X/Open Curses nor the SVr4 man pages documented the return
values of tgetent correctly, though all three shown here were in
fact returned ever since SVr1. In particular, an omission in the
X/Open Curses specification 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 X/Open Curses Issue 4 Version 2 rather than in ncurses.
[1mCompatibility with BSD termcap
ncurses provides externally visible variables to support certain
termcap applications. However, their correct usage is poorly
documented; for example, it is unclear when reading and writing
them is meaningful. In particular, some applications are reported
to declare and/or modify ospeed.
The constraint that only the first two characters of the id
parameter are looked up in the terminal database escapes many
application developers. The BSD termcap library did not require a
trailing null character after the capability identifier passed to
tgetstr, tgetnum, and tgetflag. Some applications thus assume
that the termcap interface does not require the trailing null
character for the capability identifier. ncurses disallows
matches by the termcap interface against extended capability names
that are longer than two characters; see user_caps(5).
The BSD termcap function tgetent returns the text of a termcap
entry in the buffer passed as an argument. ncurses, like other
terminfo implementations, does not store terminal type
descriptions as text. It sets the buffer contents to a null-
terminated string.
Header File
ncurses includes a termcap.h header file for compatibility with
other implementations, but it is rarely used because the other
implementations are not mutually compatible; see below.
Bill Joy originated a forerunner of termcap called “ttycap”, dated
September 1977, and released in 1BSD (March 1978). It used many
of the same function names as the later termcap, such as tgetent,
tgetflag, tgetnum, and tgetstr.
A clear descendant, the termlib library, followed in 2BSD (May
1979), adding tgoto and tputs. The former applied at that time
only to cursor positioning capabilities, thus the overly specific
name. Little changed in 3BSD (late 1979) except the addition of
test programs and a termlib man page, which documented the API
shown in section “SYNOPSIS” above.
4BSD (November 1980) renamed termlib to termcap and added another
test program. The library remained much the same through 4.3BSD
(June 1986). 4.4BSD-Lite (June 1994) refactored it, leaving the
API unchanged.
Function prototypes were a feature of ANSI C (1989). The library
long antedated the standard and thus provided no header file
declaring them. Nevertheless, the BSD sources included two
different termcap.h header files over time.
• One was used internally by jove(1) from 4.3BSD onward. It
declared global symbols for the termcap variables that it
used.
• The other appeared in 4.4BSD-Lite Release 2 (June 1995) as
part of libedit (also known as the editline library). CSRG
source history shows that this was added in mid-1992. The
libedit header file was used internally as a convenience for
compiling the editline library. It declared function
prototypes, but no global variables. NetBSD's termcap library
added this header file in mid-1994.
Meanwhile, GNU termcap began development in 1990. Its first
release (1.0) in 1991 included a termcap.h header file. Its
second (1.1) release in September 1992 modified the file to use
const for the function prototypes in the header where one would
expect parameters to be read-only. BSD termcap did not. The
prototype for tputs also differed, but in that instance, it was
libedit that differed from BSD termcap.
GNU bash(1) has bundled GNU termcap 1.3 since mid-1993 to support
its readline(3) library, and continues to use it if configured to
do so.
ncurses 1.8.1 (November 1993) provided a termcap.h file. It
reflected influence from GNU termcap and emacs(1) (rather than
jove(1)), providing the following interface:
• global symbols used by emacs,
• const-qualified function prototypes, and
• a prototype for tparam, a GNU termcap feature.
Later (in mid-1996) the tparam function was removed from ncurses.
Any two of the four implementations thus differ, and programs that
intend to work with all termcap library interfaces must account
for that fact.
X/Open Curses Issue 4, Version 2 (1996), describes these
functions, marking them as “TO BE WITHDRAWN”.
X/Open Curses Issue 7 (2009) withdrew the termcap interface (along
with the vwprintw and vwscanw functions).
If you call tgetstr to fetch column_address (ch) or any other
parameterized string capability, be aware that it is returned in
terminfo notation, not the older and not-quite-compatible termcap
notation. This does not cause problems if all you do with it is
call tgoto or tparm, which both parametrically expand term‐
info-style string capabilities as terminfo does. (If ncurses is
configured to support termcap, tgoto checks whether the string is
terminfo-style by looking for “%p” parameters or “<...>” delays,
and invokes a termcap-style parser if the string appears not to
use terminfo syntax.)
Because terminfo's syntax for padding in string capabilities
differs from termcap's, users can be surprised.
• tputs("50") in a terminfo system transmits “50” rather than
busy-waiting for 50 milliseconds.
However, if ncurses is configured to support termcap, it may
also have been configured to support BSD-style padding. In
that case, tputs inspects strings passed to it, looking for
digits at the beginning of the string.
• tputs("50") in a termcap system may busy-wait for 50
milliseconds rather than transmitting “50”.
termcap has nothing analogous to terminfo's set_attributes (sgr)
capability. One consequence is that termcap applications assume
that “me” (equivalent to terminfo's exit_attribute_mode (sgr0)
capability) does not reset the alternate character set. ncurses
inspects the data shared with the termcap interface and modifies
it as necessary to accommodate the latter's limitation in this
respect.
TCTEST — A Termcap Test Utility ⟨https://invisible-island.net/
ncurses/tctest.html⟩
curses(3X), curs_terminfo(3X), putc(3), term_variables(3X),
terminfo(5)
This page is part of the ncurses (new curses) project.
Information about the project can be found at
⟨https://invisible-island.net/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to bug-ncurses@gnu.org.
This page was obtained from the tarball ncurses-6.6.tar.gz fetched
from ⟨https://ftp.gnu.org/gnu/ncurses/⟩ on 2026-01-16. If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information
in this COLOPHON (which is not part of the original manual page),
send a mail to man-pages@man7.org
ncurses @NCURSES_MAJOR@.@NCU... 2025-08-16 curs_termcap(3X)
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HTML rendering created 2026-01-16 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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