These routines are included as a conversion aid for programs that use
- the termcap library. Their parameters are the same and the routines
+ 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.
-
The tgoto routine expands the given capability using the parameters.
o Because the capability may have padding characters, the output of
tgoto should be passed to tputs rather than some other output func-
- tion such as printf.
+ tion such as printf(3).
o While tgoto is assumed to be used for the two-parameter cursor po-
sitioning capability, termcap applications also use it for single-
@@ -147,13 +148,21 @@
first parameter is merely a placeholder.
o Normally the ncurses library is compiled with terminfo support. In
- that case, tgoto uses tparm(3x) (a more capable formatter).
+ that case, tgoto uses an internal version of tparm(3x) (a more ca-
+ pable formatter).
+
+ With terminfo support, tgoto is able to use some of the terminfo
+ features, but not all. In particular, it allows only numeric pa-
+ rameters; tparm supports string parameters.
+
+ However, tparm is not a termcap feature, and portable termcap ap-
+ plications 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.
-
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
@@ -161,6 +170,29 @@
in a system-specific coding to reflect the terminal speed.
+
+ The termcap functions provide no means for freeing memory, because
+ legacy termcap implementations used only the buffer areas provided by
+ the caller via tgetent and tgetstr. Those buffers are unused in ter-
+ minfo.
+
+ On the other hand, terminfo allocates memory. It uses setupterm to re-
+ trieve the data used by tgetent and the functions which return capabil-
+ ity 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 set-
+ ting of the TERM variable when tgetent is called. The screen(1) pro-
+ gram 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 oth-
+ er 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
@@ -168,6 +200,20 @@
Routines that return pointers return NULL on error.
+ A few special cases apply:
+
+ o If the terminal database has not been initialized, these return an
+ error.
+
+ o The calls with a string parameter (tgoto, tputs) check if the
+ string is null, or cancelled. Those return an error.
+
+ o A call to tgoto using a capability with string parameters is an er-
+ ror.
+
+ o A call to tgoto using a capability with no parameters, or more than
+ two is an error.
+
If you call tgetstr to fetch ca or any other parameterized string, be
@@ -180,19 +226,39 @@
style parser if the string does not appear to be terminfo).
Because terminfo conventions for representing padding in string capa-
- bilities differ from termcap's, tputs("50"); will put out a literal
- "50" rather than busy-waiting for 50 milliseconds. Cope with it.
+ bilities differ from termcap's, users can be surprised:
- 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
+ otputs("50") in a terminfo system will put out a literal "50" rather
+ than busy-waiting for 50 milliseconds.
+
+ o 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 dig-
+ its 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 ac-
commodate termcap's limitation in this respect.
+ These functions are provided for supporting legacy applications, and
+ should not be used in new programs:
+
+ o The XSI Curses standard, Issue 4 describes these functions. Howev-
+ er, they are marked TO BE WITHDRAWN and may be removed in future
+ versions.
+
+ o 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 re-
@@ -202,6 +268,8 @@
bility 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 applica-
tions. However, termcap applications' use of those variables is poorly
documented, e.g., not distinguishing between input and output. In par-
@@ -226,11 +294,65 @@
against extended capability names which are longer than two charac-
ters.
+ 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.
+
+
+
+ This library includes a termcap.h header, for compatibility with other
+ implementations. But the header is rarely used because the other im-
+ plementations 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 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:
+
+ o One was used internally by the jove editor in 2BSD through 4.4BSD.
+ It defined global symbols for the termcap variables which it used.
+
+ o The other appeared in 4.4BSD Lite Release 2 (mid-1993) as part of
+ libedit (also known as the editline library). The CSRG source his-
+ tory shows that this was added in mid-1992. The libedit header
+ file was used internally, as a convenience for compiling the edit-
+ line library. It declared function prototypes, but no global vari-
+ ables.
+
+ 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 ex-
+ pect 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:
+
+ o it provided declarations for a few global symbols used by emacs
+
+ o it provided function prototypes (using const).
+
+ o 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.
+