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));
The tgetent routine loads the entry for name. It returns:
This differs from the termcap library in two ways:
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:
Only the first two characters of the id parameter of tgetflag, tgetnum and tgetstr are compared in lookups.
The tgoto routine expands the given capability using the parameters.
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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(3).
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While tgoto is assumed to be used for the two-parameter
cursor positioning capability,
termcap applications also use it for single-parameter capabilities.
The tputs routine is described on the terminfo(3NCURSES) manual page. It can retrieve capabilities by either termcap or terminfo name.
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.
On the other hand, terminfo allocates memory. It uses setupterm to retrieve the data used by tgetent and the functions which return 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 memleaks(3NCURSES)).
Routines that return pointers return NULL on error.
Because terminfo conventions for representing padding in string capabilities
differ from termcap's,
users can be surprised:
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tputs("50") in a terminfo system will put out a literal ``50''
rather than busy-waiting for 50 milliseconds.
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However, if ncurses is configured to support termcap,
it may also have been configured to support the BSD-style padding.
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.
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:
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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.
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This implementation disallows matches by the termcap interface 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 descriptions as text. It sets the buffer contents to a null-terminated string.
The original BSD termcap (through 4.3BSD) had no header file which
gave function prototypes, because that was a feature of ANSI C.
BSD termcap was written several years before C was standardized.
However, there were two different termcap.h header files in the BSD
sources:
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One was used internally by the jove editor in 2BSD through 4.4BSD.
It defined global symbols for the termcap variables which it used.
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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 library 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 modified 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 prototype 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:
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it provided declarations for a few global symbols used by emacs
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it provided function prototypes (using const).
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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 implementations, which must be taken into account by programs which can work with all termcap library interfaces.
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