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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | BUGS | PORTABILITY | SEE ALSO | COLOPHON |
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curs_termcap(3X) curs_termcap(3X)
PC, UP, BC, ospeed, tgetent, tgetflag, tgetnum, tgetstr, tgoto,
tputs - curses emulation of termcap
#include <curses.h>
#include <term.h>
extern char PC;
extern char * UP;
extern char * BC;
extern @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 **area);
char *tgoto(const char *cap, int col, int row);
int tputs(const char *str, int affcnt, int (*putc)(int));
These routines are included as a conversion aid for programs that
use the termcap library. Their parameters are the same, but 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 li‐
brary does not check if the terminal description is marked
with the generic capability, or if the terminal descrip‐
tion 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 val‐
ue 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 de‐
scription 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 parame‐
ters.
• Because the capability may have padding characters, the out‐
put of tgoto should 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 cur‐
sor 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 devel‐
opers of the termcap interface chose to put the column para‐
meter first. The tgoto function swaps the order of parame‐
ters. 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 sup‐
port. 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, re‐
spectively. UP is not used by ncurses. PC is used in the tde‐
lay_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.
Releasing Memory
The termcap functions provide no means for freeing memory, be‐
cause legacy termcap implementations used only the buffer areas
provided by the caller via tgetent and tgetstr. Those buffers
are unused in terminfo.
On the other hand, terminfo allocates memory. It uses setupterm
to retrieve the data used by tgetent and the functions which re‐
turn capability values such as tgetstr. 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
setting of the TERM variable when tgetent is called. The
screen(1) program relies upon this arrangement, to improve its
performance.
An application which uses only the low-level termcap functions
could free the memory using del_curterm, because the pool is
freed using other functions (see curs_memleaks(3X)).
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.
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" para‐
meters 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, users can be surprised:
• tputs("50") in a terminfo system will put out a literal “50”
rather than busy-waiting for 50 milliseconds.
• However, if ncurses is configured to support termcap, it may
also have been configured to support the 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 wait for 50 milliseconds
rather than put out a literal “50”
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 re‐
spect.
Standards
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 in‐
terface (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 func‐
tions is to provide compatibility with the termcap library, that
is a defect in XCurses, Issue 4, Version 2 rather than in ncurs‐
es.
Compatibility with BSD Termcap
External variables are provided for support of certain termcap
applications. However, termcap applications' use of those vari‐
ables is poorly documented, e.g., not distinguishing between in‐
put 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 parame‐
ter 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 tget‐
str, tgetnum and tgetflag. Some applications assume that the
termcap interface does not require the trailing NUL for the para‐
meter name. Taking into account these issues:
• As a special case, tgetflag matched against a single-charac‐
ter 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 inter‐
face against extended capability names which are longer than
two characters.
The BSD termcap function tgetent returns the text of a termcap
entry in the buffer passed as an argument. This library (like
other terminfo implementations) does not store terminal descrip‐
tions as text. It sets the buffer contents to a null-terminated
string.
Other Compatibility
This library includes a termcap.h header, for compatibility with
other implementations. But the header is rarely used because the
other implementations are not strictly compatible.
The original BSD termcap (through 4.3BSD) had no header file
which gave function prototypes, because that was a feature of AN‐
SI C. BSD termcap was written several years before C was stan‐
dardized. However, there were two different termcap.h header
files in the BSD sources:
• One was used internally by the jove editor in 2BSD through
4.4BSD. It defined global symbols for the termcap variables
which it used.
• The other appeared in 4.4BSD Lite Release 2 (mid-1993) as
part of libedit (also known as the editline library). The
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.
The header file from libedit was added to NetBSD's termcap li‐
brary in mid-1994.
Meanwhile, GNU termcap was under development, starting in 1990.
The first release (termcap 1.0) in 1991 included a termcap.h
header. The second release (termcap 1.1) in September 1992 modi‐
fied the header to use const for the function prototypes in the
header where one would expect the parameters to be read-only.
This was a difference versus the original BSD termcap. The pro‐
totype for tputs also differed, but in that instance, it was
libedit which differed from BSD termcap.
A copy of GNU termcap 1.3 was bundled with bash in mid-1993, to
support the readline(3) library.
A termcap.h file was provided in ncurses 1.8.1 (November 1993).
That reflected influence by emacs(1) (rather than jove(1)) and
GNU termcap:
• it provided declarations for a few global symbols used by
emacs
• it provided function prototypes (using const).
• a prototype for tparam (a GNU termcap feature) was provided.
Later (in mid-1996) the tparam function was removed from ncurses.
As a result, there are differences between any of the four imple‐
mentations, which must be taken into account by programs which
can work with all termcap library interfaces.
curses(3X), putc(3), term_variables(3X), terminfo(5).
https://invisible-island.net/ncurses/tctest.html
This page is part of the ncurses (new curses) project. Informa‐
tion about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have
a bug report for this manual page, send it to
[email protected]. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨https://github.com/mirror/ncurses.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2023-03-12.) 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
[email protected]
curs_termcap(3X)
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HTML rendering created 2024-06-26 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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