1curs_termcap(3X) curs_termcap(3X)
2
6 PC, UP, BC, ospeed, tgetent, tgetflag, tgetnum, tgetstr, tgoto, tputs -
7 curses emulation of termcap
8
10 #include <curses.h>
11 #include <term.h>
12 extern char PC;
14 extern char * UP;
15 extern char * BC;
16 extern unsigned ospeed;
17 int tgetent(char *bp, const char *name);
19 int tgetflag(const char *id);
20 int tgetnum(const char *id);
21 char *tgetstr(const char *id, char **area);
22 char *tgoto(const char *cap, int col, int row);
23 int tputs(const char *str, int affcnt, int (*putc)(int));
24
26 These routines are included as a conversion aid for programs that use
27 the termcap library. Their parameters are the same, but the routines
28 are emulated using the terminfo database. Thus, they can only be used
29 to query the capabilities of entries for which a terminfo entry has
30 been compiled.
31 Initialization
33 The tgetent routine loads the entry for name. It returns:
34 1 on success,
36 0 if there is no such entry (or that it is a generic type, having
38 too little information for curses applications to run), and
39 -1 if the terminfo database could not be found.
41 This differs from the termcap library in two ways:
43 • The emulation ignores the buffer pointer bp. The termcap li‐
45 brary would store a copy of the terminal description in the area
46 referenced by this pointer. However, ncurses stores its termi‐
47 nal descriptions in compiled binary form, which is not the same
48 thing.
49 • There is a difference in return codes. The termcap library does
51 not check if the terminal description is marked with the generic
52 capability, or if the terminal description has cursor-address‐
53 ing.
54 Capability Values
56 The tgetflag routine gets the boolean entry for id, or zero if it is
57 not available.
58 The tgetnum routine gets the numeric entry for id, or -1 if it is not
60 available.
61 The tgetstr routine returns the string entry for id, or zero if it is
63 not available. Use tputs to output the returned string. The area pa‐
64 rameter is used as follows:
65 • It is assumed to be the address of a pointer to a buffer managed
67 by the calling application.
68 • However, ncurses checks to ensure that area is not NULL, and al‐
70 so that the resulting buffer pointer is not NULL. If either
71 check fails, the area parameter is ignored.
72 • If the checks succeed, ncurses also copies the return value to
74 the buffer pointed to by area, and the area value will be updat‐
75 ed to point past the null ending this value.
76 • The return value itself is an address in the terminal descrip‐
78 tion which is loaded into memory.
79 Only the first two characters of the id parameter of tgetflag, tgetnum
81 and tgetstr are compared in lookups.
82 Formatting Capabilities
84 The tgoto routine expands the given capability using the parameters.
85 • Because the capability may have padding characters, the output of
87 tgoto should be passed to tputs rather than some other output func‐
88 tion such as printf(3).
89 • While tgoto is assumed to be used for the two-parameter cursor po‐
91 sitioning capability, termcap applications also use it for single-
92 parameter capabilities.
93 Doing this shows a quirk in tgoto: most hardware terminals use cur‐
95 sor addressing with row first, but the original developers of the
96 termcap interface chose to put the column parameter first. The
97 tgoto function swaps the order of parameters. It does this also
98 for calls requiring only a single parameter. In that case, the
99 first parameter is merely a placeholder.
100 • Normally the ncurses library is compiled with terminfo support. In
102 that case, tgoto uses tparm(3X) (a more capable formatter).
103 However, tparm is not a termcap feature, and portable termcap ap‐
105 plications should not rely upon its availability.
106 The tputs routine is described on the curs_terminfo(3X) manual page.
108 It can retrieve capabilities by either termcap or terminfo name.
109 Global Variables
111 The variables PC, UP and BC are set by tgetent to the terminfo entry's
112 data for pad_char, cursor_up and backspace_if_not_bs, respectively. UP
113 is not used by ncurses. PC is used in the tdelay_output function. BC
114 is used in the tgoto emulation. The variable ospeed is set by ncurses
115 in a system-specific coding to reflect the terminal speed.
116 Releasing Memory
118 The termcap functions provide no means for freeing memory, because
119 legacy termcap implementations used only the buffer areas provided by
120 the caller via tgetent and tgetstr. Those buffers are unused in ter‐
121 minfo.
122 On the other hand, terminfo allocates memory. It uses setupterm to re‐
124 trieve the data used by tgetent and the functions which return capabil‐
125 ity values such as tgetstr. One could use
126 del_curterm(cur_term);
128 to free this memory, but there is an additional complication with
131 ncurses. It uses a fixed-size pool of storage locations, one per set‐
132 ting of the TERM variable when tgetent is called. The screen(1) pro‐
133 gram relies upon this arrangement, to improve its performance.
134 An application which uses only the low-level termcap functions could
136 free the memory using del_curterm, because the pool is freed using oth‐
137 er functions (see curs_memleaks(3X)).
138
140 Except where explicitly noted, routines that return an integer return
141 ERR upon failure and OK (SVr4 only specifies "an integer value other
142 than ERR") upon successful completion.
143 Routines that return pointers return NULL on error.
145
147 If you call tgetstr to fetch ca or any other parameterized string, be
148 aware that it will be returned in terminfo notation, not the older and
149 not-quite-compatible termcap notation. This will not cause problems if
150 all you do with it is call tgoto or tparm, which both expand terminfo-
151 style strings as terminfo. (The tgoto function, if configured to sup‐
152 port termcap, will check if the string is indeed terminfo-style by
153 looking for "%p" parameters or "$<..>" delays, and invoke a termcap-
154 style parser if the string does not appear to be terminfo).
155 Because terminfo conventions for representing padding in string capa‐
157 bilities differ from termcap's, users can be surprised:
158 • tputs("50") in a terminfo system will put out a literal “50” rather
160 than busy-waiting for 50 milliseconds.
161 • However, if ncurses is configured to support termcap, it may also
163 have been configured to support the BSD-style padding.
164 In that case, tputs inspects strings passed to it, looking for dig‐
166 its at the beginning of the string.
167 tputs("50") in a termcap system may wait for 50 milliseconds rather
169 than put out a literal “50”
170 Note that termcap has nothing analogous to terminfo's sgr string. One
172 consequence of this is that termcap applications assume me (terminfo
173 sgr0) does not reset the alternate character set. This implementation
174 checks for, and modifies the data shown to the termcap interface to ac‐
175 commodate termcap's limitation in this respect.
176
178 Standards
179 These functions are provided for supporting legacy applications, and
180 should not be used in new programs:
181 • The XSI Curses standard, Issue 4 describes these functions. Howev‐
183 er, they are marked TO BE WITHDRAWN and may be removed in future
184 versions.
185 • X/Open Curses, Issue 5 (December 2007) marked the termcap interface
187 (along with vwprintw and vwscanw) as withdrawn.
188 Neither the XSI Curses standard nor the SVr4 man pages documented the
190 return values of tgetent correctly, though all three were in fact re‐
191 turned ever since SVr1. In particular, an omission in the XSI Curses
192 documentation has been misinterpreted to mean that tgetent returns OK
193 or ERR. Because the purpose of these functions is to provide compati‐
194 bility with the termcap library, that is a defect in XCurses, Issue 4,
195 Version 2 rather than in ncurses.
196 Compatibility with BSD Termcap
198 External variables are provided for support of certain termcap applica‐
199 tions. However, termcap applications' use of those variables is poorly
200 documented, e.g., not distinguishing between input and output. In par‐
201 ticular, some applications are reported to declare and/or modify os‐
202 peed.
203 The comment that only the first two characters of the id parameter are
205 used escapes many application developers. The original BSD 4.2 termcap
206 library (and historical relics thereof) did not require a trailing null
207 NUL on the parameter name passed to tgetstr, tgetnum and tgetflag.
208 Some applications assume that the termcap interface does not require
209 the trailing NUL for the parameter name. Taking into account these is‐
210 sues:
211 • As a special case, tgetflag matched against a single-character
213 identifier provided that was at the end of the terminal descrip‐
214 tion. You should not rely upon this behavior in portable programs.
215 This implementation disallows matches against single-character ca‐
216 pability names.
217 • This implementation disallows matches by the termcap interface
219 against extended capability names which are longer than two charac‐
220 ters.
221 The BSD termcap function tgetent returns the text of a termcap entry in
223 the buffer passed as an argument. This library (like other terminfo
224 implementations) does not store terminal descriptions as text. It sets
225 the buffer contents to a null-terminated string.
226 Other Compatibility
228 This library includes a termcap.h header, for compatibility with other
229 implementations. But the header is rarely used because the other im‐
230 plementations are not strictly compatible.
231 The original BSD termcap (through 4.3BSD) had no header file which gave
233 function prototypes, because that was a feature of ANSI C. BSD termcap
234 was written several years before C was standardized. However, there
235 were two different termcap.h header files in the BSD sources:
236 • One was used internally by the jove editor in 2BSD through 4.4BSD.
238 It defined global symbols for the termcap variables which it used.
239 • The other appeared in 4.4BSD Lite Release 2 (mid-1993) as part of
241 libedit (also known as the editline library). The CSRG source his‐
242 tory shows that this was added in mid-1992. The libedit header
243 file was used internally, as a convenience for compiling the edit‐
244 line library. It declared function prototypes, but no global vari‐
245 ables.
246 The header file from libedit was added to NetBSD's termcap library in
248 mid-1994.
249 Meanwhile, GNU termcap was under development, starting in 1990. The
251 first release (termcap 1.0) in 1991 included a termcap.h header. The
252 second release (termcap 1.1) in September 1992 modified the header to
253 use const for the function prototypes in the header where one would ex‐
254 pect the parameters to be read-only. This was a difference versus the
255 original BSD termcap. The prototype for tputs also differed, but in
256 that instance, it was libedit which differed from BSD termcap.
257 A copy of GNU termcap 1.3 was bundled with bash in mid-1993, to support
259 the readline(3) library.
260 A termcap.h file was provided in ncurses 1.8.1 (November 1993). That
262 reflected influence by emacs(1) (rather than jove(1)) and GNU termcap:
263 • it provided declarations for a few global symbols used by emacs
265 • it provided function prototypes (using const).
267 • a prototype for tparam (a GNU termcap feature) was provided.
269 Later (in mid-1996) the tparam function was removed from ncurses. As a
271 result, there are differences between any of the four implementations,
272 which must be taken into account by programs which can work with all
273 termcap library interfaces.
274
276 curses(3X), putc(3), term_variables(3X), terminfo(5).
277 https://invisible-island.net/ncurses/tctest.html
279 curs_termcap(3X)