- 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.
+ ncurses provides the foregoing variables and functions as a
+ compatibility layer for programs that use the termcap library. The API
+ is the same, but behavior is emulated using the terminfo database.
+ Thus, it can be used only to query the capabilities of terminal
+ database entries for which a terminfo entry has been compiled.
- The tgetent routine loads the entry for name. It returns:
+ tgetent loads the terminal database entry for name; see term(7). This
+ must be done before calling any of the other functions. It returns
- 1 on success,
+ 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
+ 0 if there is no such entry (or if the matching entry describes a
+ generic terminal, having too little information for curses
+ applications to run), and
- -1 if the terminfo database could not be found.
+ -1 if the terminfo database could not be found.
- This differs from the termcap library in two ways:
+ This implementation differs from those of historical termcap libraries.
- o 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.
+ oncurses ignores the buffer pointer bp, as do other termcap
+ implementations conforming to portions of X/Open Curses now
+ withdrawn. The BSD termcap library would store a copy of the
+ terminal type description in the area referenced by this
+ pointer. terminfo stores terminal type descriptions in compiled
+ form, which is not the same thing.
- o There is a difference in return codes. The termcap library does
- not check if the terminal description is marked with the generic
- capability, or if the terminal description has cursor-
- addressing.
+ o The meanings of the return values differ. The BSD termcap
+ library does not check whether the terminal type description
+ includes the generic (gn) capability, nor whether the terminal
+ type description supports an addressable cursor, a property
+ essential for any curses implementation to operate.
-
- 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
+
+ tgetflag reports the Boolean entry for id, or zero 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:
+ tgetnum obtains the numeric entry for id, or -1 if it is not available.
+
+ tgetstr returns the string entry for id, or NULL if it is not
+ available. Use tputs to output the string returned. The area
+ parameter is used as follows.
o It is assumed to be the address of a pointer to a buffer managed
by the calling application.
- o 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.
-
- o If the checks succeed, ncurses also copies the return value to
- the buffer pointed to by area, and the area value will be
- updated to point past the null ending this value.
+ o However, ncurses checks to ensure that area is not NULL, and
+ also that the resulting buffer pointer is not NULL. If either
+ check fails, area is ignored.
- o The return value itself is an address in the terminal
- description which is loaded into memory.
+ o If the checks succeed, ncurses also copies the return value to
+ the buffer pointed to by area, and the library updates area to
+ point past the null character terminating this value.
- Only the first two characters of the id parameter of tgetflag, tgetnum
- and tgetstr are compared in lookups.
+ o The return value itself is an address in the terminal type
+ description loaded into memory.
-
+ String capabilities can be parameterized; see subsection "Parameterized
+ Strings" in terminfo(5). tgoto applies its second and third arguments
+ to the parametric placeholders in the capability stored in the first
+ argument.
- o 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).
+ o The capability may contain padding specifications; see subsection
+ "Delays and Padding" of terminfo(5). The output of tgoto should
+ thus be passed to tputs rather than some other output function such
+ as printf(3).
o While tgoto is assumed to be used for the two-parameter cursor
- positioning capability, termcap applications also use it for
+ positioning capability, termcap applications also use it for
single-parameter capabilities.
- Doing this shows a quirk in tgoto: most hardware terminals use
+ Doing so reveals a quirk in tgoto: most hardware terminals use
cursor addressing with row first, but the original developers of
- the termcap interface chose to put the column parameter first. The
- tgoto function swaps the order of parameters. It does this also
- for calls requiring only a single parameter. In that case, the
- first parameter is merely a placeholder.
+ the termcap interface chose to put the col (column) parameter
+ first. The tgoto function swaps the order of its parameters. It
+ does this even for calls requiring only a single parameter. In
+ that case, the first parameter is merely a placeholder.
- o Normally the ncurses library is compiled with terminfo support. In
- that case, tgoto uses an internal version of tparm(3x) (a more
- capable formatter).
+ o Normally the ncurses library is compiled without full termcap
+ support. In that case, tgoto uses an internal version of tparm(3x)
+ (a more capable function).
- With terminfo support, tgoto is able to use some of the terminfo
- features, but not all. In particular, it allows only numeric
+ Because it uses tparm internally, tgoto is able to use some term-
+ info features, but not all. In particular, it allows only numeric
parameters; tparm supports string parameters.
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.
+ tputs is described in curs_terminfo(3x). It can retrieve capabilities
+ by either termcap or terminfo code.
- The variables PC, UP and BC are set by tgetent to the terminfo entry's
+ 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.
+ is not used by ncurses. PC is used by delay_output(3x). BC is used by
+ tgoto emulation. The variable ospeed is set by ncurses using a system-
+ specific encoding to indicate the terminal's data rate.
- 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
- terminfo.
+ The termcap functions provide no means of freeing memory, because
+ legacy termcap implementations used only the buffer areas provided by
+ the caller via tgetent and tgetstr. Those buffers are unused in term-
+ info.
+
+ By contrast, terminfo allocates memory. It uses setupterm(3x) to
+ obtain the data used by tgetent and the functions that retrieve
+ capability values. 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 value
+ of the terminal name parameter given to tgetent. The screen(1) program
+ relies upon this arrangement to improve its performance.
- 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
+ An application that uses only the termcap functions, not the higher
+ level curses API, could release the memory using del_curterm(3x),
+ because the pool is freed using other functions; see curs_memleaks(3x).
- del_curterm(cur_term);
+
+ The return values of tgetent, tgetflag, tgetname, and tgetstr are
+ documented above.
- 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.
+ tgoto returns NULL on error. Error conditions include:
- 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)).
+ o uninitialized state (tgetent was not called successfully),
+ ocap being a null pointer,
-
- 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.
+ ocap referring to a canceled capability,
- Routines that return pointers return NULL on error.
+ ocap being a capability with string-valued parameters (a term-
+ info-only feature), and
- A few special cases apply:
+ ocap being a capability with more than two parameters.
- o If the terminal database has not been initialized, these return an
- error.
+ See curs_terminfo(3x) regarding tputs.
- 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
- error.
+
+ ncurses compares only the first two characters of the id parameter of
+ tgetflag, tgetnum, and tgetstr to the capability names in the database.
- o A call to tgoto using a capability with more than two parameters is
- an error.
+
+ These functions are no longer standardized (and the variables never
+ were); ncurses provides them to support legacy applications. They
+ should not be used in new programs.
-
- 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" parameters 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:
+
+ o X/Open Curses, Issue 4, Version 2 (1996), describes these
+ functions, marking them as "TO BE WITHDRAWN".
+
+ o X/Open Curses, Issue 7 (2009) marks the termcap interface (along
+ with vwprintw and vwscanw) as withdrawn.
+
+ Neither X/Open Curses nor the SVr4 man pages documented the return
+ values of tgetent correctly, though all three shown here were in fact
+ returned ever since SVr1. In particular, an omission in the X/Open
+ Curses specification 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
+ X/Open Curses, Issue 4, Version 2 rather than in ncurses.
+
+ CompatibilitywithBSDtermcap
+ Externally visible variables are provided for support of certain
+ termcap applications. However, their correct usage is poorly
+ documented; for example, it is unclear when reading and writing them is
+ meaningful. In particular, some applications are reported to declare
+ and/or modify ospeed.
+
+ The constraint that only the first two characters of the id parameter
+ are used escapes many application developers. The BSD termcap library
+ did not require a trailing null character on the capability identifier
+ passed to tgetstr, tgetnum, and tgetflag. Some applications thus
+ assume that the termcap interface does not require the trailing null
+ character for the capability identifier.
+
+ oncurses disallows matches by the termcap interface against extended
+ capability names that are longer than two characters; see
+ user_caps(5).
+
+ 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 type 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
+ implementations are not strictly compatible.
- 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.
+
+ Bill Joy originated a forerunner of termcap called "ttycap", dated
+ September 1977, and released in 1BSD (March 1978). It used many of the
+ same function names as the later termcap, such as tgetent, tgetflag,
+ tgetnum, and tgetstr.
- In that case, tputs inspects strings passed to it, looking for
- digits at the beginning of the string.
+ A clear descendant, the termlib library, followed in 2BSD (May 1979),
+ adding tgoto and tputs. The former applied at that time only to cursor
+ positioning capabilities, thus the overly specific name. Little
+ changed in 3BSD (late 1979) except the addition of test programs and a
+ termlib man page, which documented the API shown in section "SYNOPSIS"
+ above.
- tputs("50") in a termcap system may wait for 50 milliseconds rather
- than put out a literal "50"
+ 4BSD (November 1980) renamed termlib to termcap and added another test
+ program. The library remained much the same though 4.3BSD (June 1986).
+ 4.4BSD-Lite (June 1994) refactored it, leaving the API unchanged.
- 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.
+ Function prototypes were a feature of ANSI C (1989). The library long
+ antedated the standard and thus provided no header file declaring them.
+ Nevertheless, the BSD sources included two different termcap.h header
+ files over time.
+ o One was used internally by jove(1) from 4.3BSD onward. It declared
+ global symbols for the termcap variables that it used.
-
+ o The other appeared in 4.4BSD-Lite Release 2 (June 1995) as part of
+ libedit (also known as the editline library). 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.
+ This header file was added to NetBSD's termcap library in mid-1994.
-
- 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.
- However, 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
- 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:
-
- o 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.
-
- o 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.
-
-
-
- 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.
+ Meanwhile, GNU termcap began development in 1990. Its first release
+ (1.0) in 1991 included a termcap.h header. Its second (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. BSD termcap did not. The prototype for tputs also
+ differed, but in that instance, it was libedit that differed from BSD
+ termcap.
+
+ GNU termcap 1.3 was bundled with bash(1) in mid-1993 to support the
+ readline(3) library.
+
+ ncurses 1.8.1 (November 1993) provided a termcap.h file. It reflected
+ influence from GNU termcap and emacs(1) (rather than jove(1)),
+ providing the following interface:
- 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 global symbols used by emacs,
- 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.
+ oconst-qualified function prototypes, and
- 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
- 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.
+ o a prototype for tparam, a GNU termcap feature.
- The header file from libedit was added to NetBSD's termcap library in
- mid-1994.
+ Later (in mid-1996) the tparam function was removed from ncurses. Any
+ two of the four implementations thus differ, and programs that intend
+ to work with all termcap library interfaces must account for that fact.
- 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.
+
+ If you call tgetstr to fetch column_address (ch) or any other
+ parameterized string capability, be aware that it is returned in term-
+ info notation, not the older and not-quite-compatible termcap notation.
+ This does not cause problems if all you do with it is call tgoto or
+ tparm, which both parametrically expand terminfo-style string
+ capabilities as terminfo does. (If ncurses is configured to support
+ termcap,tgoto checks whether the string is terminfo-style by looking
+ for "%p" parameters or "<...>" delays, and invokes a termcap-style
+ parser if the string appears not to use terminfo syntax.)
+
+ Because terminfo's syntax for padding in string capabilities differs
+ from termcap's, users can be surprised.
- 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:
+ otputs("50") in a terminfo system transmits "50" rather than busy-
+ waiting for 50 milliseconds.
- o it provided declarations for a few global symbols used by emacs
+ o However, if ncurses is configured to support termcap, it may also
+ have been configured to support BSD-style padding.
- o it provided function prototypes (using const).
+ In that case, tputs inspects strings passed to it, looking for
+ digits at the beginning of the string.
- o a prototype for tparam (a GNU termcap feature) was provided.
+ tputs("50") in a termcap system may busy-wait for 50 milliseconds
+ rather than transmitting "50".
- 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.
+ termcap has nothing analogous to terminfo's set_attributes (sgr)
+ capability. One consequence is that termcap applications assume that
+ "me" (equivalent to terminfo's exit_attribute_mode (sgr0) capability)
+ does not reset the alternate character set. ncurses checks for, and
+ modifies the data shared with, the termcap interface to accommodate the
+ latter's limitation in this respect.