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

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:

          •   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-addressing.

   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 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.

   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(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  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 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.

   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 terminfo.

       On the other hand, terminfo allocates memory.  It uses setupterm to retrieve the data used
       by tgetent and the functions which return capability 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 setting of the TERM variable when tgetent is
       called.  The screen(1) program 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 other functions (see memleaks(3NCURSES)).

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, users can be surprised:

• tputs("50") in a terminfo system will put out a literal “50” rather than busy-waiting
for 50 milliseconds.

• 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 digits 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 accommodate termcap's limitation in this respect.

PORTABILITY