Manual Pages  — curs_termcap

 PC,  UP,  BC,  ospeed,  tgetent,  tgetflag,  tgetnum,  tgetstr,  tgoto,  tputs - curses emulation of termcap

SYNOPSIS DESCRIPTION Initialization Retrieving Capability Values Applying String Capabilities Global Variables Releasing Memory RETURN VALUE NOTES PORTABILITY Standards Compatibility with BSD termcap Header File HISTORY BUGS SEE ALSO

#include <curses.h>
#include <term.h>

char PC;
char * UP;
char * BC;
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));

 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  term info database. Thus, it can be used only to query the capabilities of terminal database entries for which a  term info entry has been compiled.

 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,
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  term info database could not be found.

This implementation differs from those of historical termcap libraries.

»	ncurses ignores the buffer pointer bp, as do other termcap implementations conforming to portions of X/Open Curses now withdrawn.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.  term info stores terminal type descriptions in compiled form, which is not the same thing.
»	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.

 tgetflag reports the Boolean entry for id, or zero if it is not available.

 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.

»	It is assumed to be the address of a pointer to a buffer managed by the calling application.
»	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.
»	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.
»	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.

»	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).
»	While  tgoto is assumed to be used for the two-parameter cursor positioning capability, termcap applications also use it for single-parameter capabilities.
	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 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.
»	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).
	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.

 tputs is described in  curs_terminfo(3X). It can retrieve capabilities by either termcap or  term info code.

The variables PC, UP and BC are set by  tgetent to the  term info entry's data for  pad_char,  cursor_up and  backspace_if_not_bs, respectively. UP 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 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,  term info 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.

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).

The return values of  tgetent,  tgetflag,  tgetname, and  tgetstr are documented above.

 tgoto returns NULL on error. Error conditions include:

»	uninitialized state ( tgetent was not called successfully),
»	cap being a null pointer,
»	cap referring to a canceled capability,
»	cap being a capability with string-valued parameters (a  term info-only feature), and
»	cap being a capability with more than two parameters.

See  curs_terminfo(3X) regarding  tputs.

 ncurses compares only the first two characters of the id parameter of  tgetflag,  tgetnum, and  tgetstr to the capability names in the database.

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.

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.

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.

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.

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.

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.

»	One was used internally by jove(1) from 4.3BSD onward. It declared global symbols for the termcap variables that it used.
»	The other appeared in 4.4BSD-Lite Release 2 (June 1995) as part of libedit (also known as the  edit line 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  edit line library. It declared function prototypes, but no global variables. This header file was added to NetBSD's termcap library in mid-1994.

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:

»	global symbols used by emacs,
»	const-qualified function prototypes, and
»	a prototype for tparam, a GNU termcap feature.

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.

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  term info-style string capabilities as  term info does. (If  ncurses is configured to support termcap,  tgoto checks whether the string is  term info-style by looking for %p parameters or <...> delays, and invokes a termcap-style parser if the string appears not to use  term info syntax.)

Because  term info's syntax for padding in string capabilities differs from termcap's, users can be surprised.

»	tputs("50") in a  term info system transmits 50 rather than busy-waiting for 50 milliseconds.
»	However, if  ncurses is configured to support termcap, it may also have been configured to support BSD-style padding.
	In that case,  tputs inspects strings passed to it, looking for digits at the beginning of the string.
	tputs("50") in a termcap system may busy-wait for 50 milliseconds rather than transmitting 50.

termcap has nothing analogous to  term info's  set_attributes (sgr) capability. One consequence is that termcap applications assume that me (equivalent to  term info'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.