curs_termcap 3x

curs_termcap(3x)                                              curs_termcap(3x)


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


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

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


       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.


       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:

          o   The  emulation  ignores  the buffer pointer bp.  The termcap li-
              brary would store a copy of the terminal description in the area
              referenced  by this pointer.  However, ncurses stores its termi-
              nal descriptions in compiled binary form, which is not the  same

          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-address-

Capability Values

       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 pa-
       rameter 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 al-
              so 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 updat-
              ed to point past the null ending this value.

          o   The  return  value itself is an address in the terminal descrip-
              tion which is loaded into memory.

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

Formatting Capabilities

       The tgoto routine expands the given capability using the parameters.

       o   Because  the  capability may have padding characters, the output of
           tgoto should be passed to tputs rather than some other output func-
           tion such as printf(3).

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

           Doing this shows a quirk in tgoto: most hardware terminals use cur-
           sor 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.

       o   Normally the ncurses library is compiled with terminfo support.  In
           that  case, tgoto uses an internal version of tparm(3x) (a more ca-
           pable formatter).

           With terminfo support, tgoto is able to use some  of  the  terminfo
           features,  but  not all.  In particular, it allows only numeric pa-
           rameters; tparm supports string parameters.

           However, tparm is not a termcap feature, and portable  termcap  ap-
           plications 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.

Global Variables

       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.

Releasing Memory

       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  ter-

       On the other hand, terminfo allocates memory.  It uses setupterm to re-
       trieve the data used by tgetent and the functions which return capabil-
       ity values such as tgetstr.  One could use


       to  free  this  memory,  but  there  is an additional complication with
       ncurses.  It uses a fixed-size pool of storage locations, one per  set-
       ting  of  the TERM variable when tgetent is called.  The screen(1) pro-
       gram relies upon this arrangement, to improve its performance.

       An application which uses only the low-level  termcap  functions  could
       free the memory using del_curterm, because the pool is freed using oth-
       er functions (see curs_memleaks(3x)).


       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.

       A few special cases apply:

       o   If the terminal database has not been initialized, these return  an

       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 er-

       o   A call to tgoto using a capability with more than two parameters is
           an error.


       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  sup-
       port  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 capa-
       bilities differ from termcap's, users can be surprised:

       o   tputs("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.

           In that case, tputs inspects strings passed to it, looking for dig-
           its at the beginning of the string.

           tputs("50") in a termcap system may wait for 50 milliseconds rather
           than put out a literal "50"

       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 ac-
       commodate termcap's limitation in this respect.



       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.  Howev-
           er, they are marked TO BE WITHDRAWN and may be  removed  in  future

       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 re-
       turned 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  compati-
       bility  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 applica-
       tions.  However, termcap applications' use of those variables is poorly
       documented, e.g., not distinguishing between input and output.  In par-
       ticular,  some  applications  are reported to declare and/or modify os-

       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 is-

       o   As a special case,  tgetflag  matched  against  a  single-character
           identifier  provided  that  was at the end of the terminal descrip-
           tion.  You should not rely upon this behavior in portable programs.
           This  implementation disallows matches against single-character ca-
           pability names.

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

       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  im-
       plementations 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 sources:

       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.

       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 his-
           tory  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 vari-

       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 ex-
       pect  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.

       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:

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

       o   it provided function prototypes (using const).

       o   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.


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