# curs_termcap 3x

    curs_termcap(3x)                                              curs_termcap(3x)

## NAME

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

## SYNOPSIS

           #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));

## DESCRIPTION

           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.

### Initialization

           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
                  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-address-
                  ing.

### 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
           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 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 tparm(3x) (a more capable formatter).

               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-
           minfo.

           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

                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 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)).

## RETURN VALUE

           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

           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.

## PORTABILITY

### Standards

           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
               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  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-
           peed.

           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-
           sues:

           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-
               ters.

           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-
               ables.

           The  header  file from libedit was added to NetBSD's termcap library in
           mid-1994.

           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.

## SEE ALSO

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

           https://invisible-island.net/ncurses/tctest.html

                                                                  curs_termcap(3x)