Ubuntu Manpage: PC, UP, BC, ospeed, tgetent, tgetflag, tgetnum, tgetstr, tgoto, tputs

Provided by: ncurses-doc_6.2-0ubuntu2.1_all

NAME

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

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 parame‐
       ters 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.

   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:

          •   The emulation ignores the buffer pointer bp.  The termcap library would store a copy of the termi‐
              nal description in the area referenced by this pointer.  However, ncurses stores its terminal  de‐
              scriptions 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 de‐
              scription is marked with the generic capability, or if the  terminal  description  has  cursor-ad‐
              dressing.

   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 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 point‐
              er 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.

   FORMATTING CAPABILITIES
       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 appli‐
           cations 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  parame‐
           ter.  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 terminfo(3NCURSES) 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.

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 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,
       tputs("50"); will put out a literal “50” rather than busy-waiting for 50 milliseconds.  Cope with it.

       Note  that termcap has nothing analogous to terminfo's sgr string.  One consequence of this is that term‐
       cap applications assume me (terminfo sgr0) does not reset the alternate character set.  This  implementa‐
       tion checks for, and modifies the data shown to the termcap interface to accommodate termcap's limitation
       in this respect.

PORTABILITY

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.

External variables are provided for support of certain termcap applications. However, termcap applica‐
tions' 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 de‐
velopers. The original BSD 4.2 termcap library (and historical relics thereof) did not require a trail‐
ing 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.