PC(3x) — Linux manual page


curs_termcap(3X)                                            curs_termcap(3X)

NAME         top

       PC, UP, BC, ospeed, tgetent, tgetflag, tgetnum, tgetstr, tgoto, tputs
       - direct curses interface to the terminfo capability database

SYNOPSIS         top

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

       extern char PC;
       extern char * UP;
       extern char * BC;
       extern @NCURSES_OSPEED@ 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));

DESCRIPTION         top

       These routines are included as a conversion aid for programs that use
       the termcap library.  Their parameters are the same and 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 tgetent routine loads the entry for name.  It returns:

          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

          -1 if the terminfo database could not be found.

       This differs from the termcap library in two ways:

          •   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.

          •   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-

       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

       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:

          •   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, the area parameter is ignored.

          •   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.

          •   The return value itself is an address in the terminal
              description which is loaded into memory.

       Only the first two characters of the id parameter of tgetflag,
       tgetnum and tgetstr are compared in lookups.

       The tgoto routine expands the given capability using the parameters.

       •   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.

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

           Doing this shows 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.

       •   Normally the ncurses library is compiled with terminfo support.
           In that case, tgoto uses tparm(3X) (a more capable formatter).

           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.

       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.

RETURN VALUE         top

       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.

       Routines that return pointers return NULL on error.

BUGS         top

       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

       Because terminfo conventions for representing padding in string
       capabilities differ from termcap's, tputs("50"); will put out a
       literal “50” rather than busy-waiting for 50 milliseconds.  Cope with

       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.

PORTABILITY         top

       These functions are provided for supporting legacy applications, and
       should not be used in new programs:

       •   The XSI Curses standard, Issue 4 describes these functions.
           However, they are marked TO BE WITHDRAWN and may be removed in
           future versions.

       •   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.

   Compatibility with BSD Termcap
       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:

       •   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.

       •   This implementation disallows matches by the termcap interface
           against extended capability names which are longer than two

       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.

   Other Compatibility
       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.

       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

       •   One was used internally by the jove editor in 2BSD through
           4.4BSD.  It defined global symbols for the termcap variables
           which it used.

       •   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.

       The header file from libedit was added to NetBSD's termcap library in

       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 library.

       A termcap.h file was provided in ncurses 1.8.1 (November 1993).  That
       reflected influence by emacs (rather than jove) and GNU termcap:

       •   it provided declarations for a few global symbols used by emacs

       •   it provided function prototypes (using const).

       •   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.

SEE ALSO         top

       curses(3X), terminfo(5), term_variables(3X), putc(3).


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