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 an internal version of tparm(3X) (a more ca‐
103 pable formatter).
104 With terminfo support, tgoto is able to use some of the terminfo
106 features, but not all. In particular, it allows only numeric pa‐
107 rameters; tparm supports string parameters.
108 However, tparm is not a termcap feature, and portable termcap ap‐
110 plications should not rely upon its availability.
111 The tputs routine is described on the curs_terminfo(3X) manual page.
113 It can retrieve capabilities by either termcap or terminfo name.
114 Global Variables
116 The variables PC, UP and BC are set by tgetent to the terminfo entry's
117 data for pad_char, cursor_up and backspace_if_not_bs, respectively. UP
118 is not used by ncurses. PC is used in the tdelay_output function. BC
119 is used in the tgoto emulation. The variable ospeed is set by ncurses
120 in a system-specific coding to reflect the terminal speed.
121 Releasing Memory
123 The termcap functions provide no means for freeing memory, because
124 legacy termcap implementations used only the buffer areas provided by
125 the caller via tgetent and tgetstr. Those buffers are unused in ter‐
126 minfo.
127 On the other hand, terminfo allocates memory. It uses setupterm to re‐
129 trieve the data used by tgetent and the functions which return capabil‐
130 ity values such as tgetstr. One could use
131 del_curterm(cur_term);
133 to free this memory, but there is an additional complication with
136 ncurses. It uses a fixed-size pool of storage locations, one per set‐
137 ting of the TERM variable when tgetent is called. The screen(1) pro‐
138 gram relies upon this arrangement, to improve its performance.
139 An application which uses only the low-level termcap functions could
141 free the memory using del_curterm, because the pool is freed using oth‐
142 er functions (see curs_memleaks(3X)).
143
145 Except where explicitly noted, routines that return an integer return
146 ERR upon failure and OK (SVr4 only specifies "an integer value other
147 than ERR") upon successful completion.
148 Routines that return pointers return NULL on error.
150 A few special cases apply:
152 • If the terminal database has not been initialized, these return an
154 error.
155 • The calls with a string parameter (tgoto, tputs) check if the
157 string is null, or cancelled. Those return an error.
158 • A call to tgoto using a capability with string parameters is an er‐
160 ror.
161 • A call to tgoto using a capability with more than two parameters is
163 an error.
164
166 If you call tgetstr to fetch ca or any other parameterized string, be
167 aware that it will be returned in terminfo notation, not the older and
168 not-quite-compatible termcap notation. This will not cause problems if
169 all you do with it is call tgoto or tparm, which both expand terminfo-
170 style strings as terminfo. (The tgoto function, if configured to sup‐
171 port termcap, will check if the string is indeed terminfo-style by
172 looking for "%p" parameters or "$<..>" delays, and invoke a termcap-
173 style parser if the string does not appear to be terminfo).
174 Because terminfo conventions for representing padding in string capa‐
176 bilities differ from termcap's, users can be surprised:
177 • tputs("50") in a terminfo system will put out a literal “50” rather
179 than busy-waiting for 50 milliseconds.
180 • However, if ncurses is configured to support termcap, it may also
182 have been configured to support the BSD-style padding.
183 In that case, tputs inspects strings passed to it, looking for dig‐
185 its at the beginning of the string.
186 tputs("50") in a termcap system may wait for 50 milliseconds rather
188 than put out a literal “50”
189 Note that termcap has nothing analogous to terminfo's sgr string. One
191 consequence of this is that termcap applications assume me (terminfo
192 sgr0) does not reset the alternate character set. This implementation
193 checks for, and modifies the data shown to the termcap interface to ac‐
194 commodate termcap's limitation in this respect.
195
197 Standards
198 These functions are provided for supporting legacy applications, and
199 should not be used in new programs:
200 • The XSI Curses standard, Issue 4 describes these functions. Howev‐
202 er, they are marked TO BE WITHDRAWN and may be removed in future
203 versions.
204 • X/Open Curses, Issue 5 (December 2007) marked the termcap interface
206 (along with vwprintw and vwscanw) as withdrawn.
207 Neither the XSI Curses standard nor the SVr4 man pages documented the
209 return values of tgetent correctly, though all three were in fact re‐
210 turned ever since SVr1. In particular, an omission in the XSI Curses
211 documentation has been misinterpreted to mean that tgetent returns OK
212 or ERR. Because the purpose of these functions is to provide compati‐
213 bility with the termcap library, that is a defect in XCurses, Issue 4,
214 Version 2 rather than in ncurses.
215 Compatibility with BSD Termcap
217 External variables are provided for support of certain termcap applica‐
218 tions. However, termcap applications' use of those variables is poorly
219 documented, e.g., not distinguishing between input and output. In par‐
220 ticular, some applications are reported to declare and/or modify os‐
221 peed.
222 The comment that only the first two characters of the id parameter are
224 used escapes many application developers. The original BSD 4.2 termcap
225 library (and historical relics thereof) did not require a trailing null
226 NUL on the parameter name passed to tgetstr, tgetnum and tgetflag.
227 Some applications assume that the termcap interface does not require
228 the trailing NUL for the parameter name. Taking into account these is‐
229 sues:
230 • As a special case, tgetflag matched against a single-character
232 identifier provided that was at the end of the terminal descrip‐
233 tion. You should not rely upon this behavior in portable programs.
234 This implementation disallows matches against single-character ca‐
235 pability names.
236 • This implementation disallows matches by the termcap interface
238 against extended capability names which are longer than two charac‐
239 ters.
240 The BSD termcap function tgetent returns the text of a termcap entry in
242 the buffer passed as an argument. This library (like other terminfo
243 implementations) does not store terminal descriptions as text. It sets
244 the buffer contents to a null-terminated string.
245 Other Compatibility
247 This library includes a termcap.h header, for compatibility with other
248 implementations. But the header is rarely used because the other im‐
249 plementations are not strictly compatible.
250 The original BSD termcap (through 4.3BSD) had no header file which gave
252 function prototypes, because that was a feature of ANSI C. BSD termcap
253 was written several years before C was standardized. However, there
254 were two different termcap.h header files in the BSD sources:
255 • One was used internally by the jove editor in 2BSD through 4.4BSD.
257 It defined global symbols for the termcap variables which it used.
258 • The other appeared in 4.4BSD Lite Release 2 (mid-1993) as part of
260 libedit (also known as the editline library). The CSRG source his‐
261 tory shows that this was added in mid-1992. The libedit header
262 file was used internally, as a convenience for compiling the edit‐
263 line library. It declared function prototypes, but no global vari‐
264 ables.
265 The header file from libedit was added to NetBSD's termcap library in
267 mid-1994.
268 Meanwhile, GNU termcap was under development, starting in 1990. The
270 first release (termcap 1.0) in 1991 included a termcap.h header. The
271 second release (termcap 1.1) in September 1992 modified the header to
272 use const for the function prototypes in the header where one would ex‐
273 pect the parameters to be read-only. This was a difference versus the
274 original BSD termcap. The prototype for tputs also differed, but in
275 that instance, it was libedit which differed from BSD termcap.
276 A copy of GNU termcap 1.3 was bundled with bash in mid-1993, to support
278 the readline(3) library.
279 A termcap.h file was provided in ncurses 1.8.1 (November 1993). That
281 reflected influence by emacs(1) (rather than jove(1)) and GNU termcap:
282 • it provided declarations for a few global symbols used by emacs
284 • it provided function prototypes (using const).
286 • a prototype for tparam (a GNU termcap feature) was provided.
288 Later (in mid-1996) the tparam function was removed from ncurses. As a
290 result, there are differences between any of the four implementations,
291 which must be taken into account by programs which can work with all
292 termcap library interfaces.
293
295 curses(3X), putc(3), term_variables(3X), terminfo(5).
296 https://invisible-island.net/ncurses/tctest.html
298 curs_termcap(3X)