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.\" $Id: curs_termcap.3x,v 1.37 2018/01/23 10:14:38 tom Exp $
.TH curs_termcap 3X ""
.de bP
.ie n  .IP \(bu 4
.el    .IP \(bu 2
..
.na
.hy 0
.ds n 5
.SH NAME
\fBPC\fR,
\fBUP\fR,
\fBBC\fR,
\fBospeed\fR,
\fBtgetent\fR,
\fBtgetflag\fR,
\fBtgetnum\fR,
\fBtgetstr\fR,
\fBtgoto\fR,
\fBtputs\fR \- direct \fBcurses\fR interface to the terminfo capability database
.ad
.hy
.SH SYNOPSIS
\fB#include <curses.h>\fR
.br
\fB#include <term.h>\fR
.sp
\fBextern char PC;\fR
.br
\fBextern char * UP;\fR
.br
\fBextern char * BC;\fR
.br
\fBextern unsigned ospeed;\fR
.sp
\fBint tgetent(char *bp, const char *name);\fR
.br
\fBint tgetflag(char *id);\fR
.br
\fBint tgetnum(char *id);\fR
.br
\fBchar *tgetstr(char *id, char **area);\fR
.br
\fBchar *tgoto(const char *cap, int col, int row);\fR
.br
\fBint tputs(const char *str, int affcnt, int (*putc)(int));\fR
.br
.SH DESCRIPTION
These routines are included as a conversion aid for programs that use
the \fItermcap\fR library.  Their parameters are the same and the
routines are emulated using the \fIterminfo\fR database.  Thus, they
can only be used to query the capabilities of entries for which a
terminfo entry has been compiled.
.SS INITIALIZATION
.PP
The \fBtgetent\fR routine loads the entry for \fIname\fR.
It returns:
.RS 3
.TP 3
1
on success,
.TP 3
0
if there is no such entry
(or that it is a generic type, having too little information for curses
applications to run), and
.TP 3
\-1
if the terminfo database could not be found.
.RE
.PP
This differs from the \fItermcap\fP library in two ways:
.RS 3
.bP
The emulation ignores the buffer pointer \fIbp\fR.
The \fItermcap\fP 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.
.bP
There is a difference in return codes.
The \fItermcap\fP library does not check if the terminal
description is marked with the \fIgeneric\fP capability,
or if the terminal description has cursor-addressing.
.RE
.SS CAPABILITY VALUES
.PP
The \fBtgetflag\fR routine gets the boolean entry for \fIid\fR,
or zero if it is not available.
.PP
The \fBtgetnum\fR routine gets the numeric entry for \fIid\fR,
or \-1 if it is not available.
.PP
The \fBtgetstr\fR routine returns the string entry for \fIid\fR,
or zero if it is not available.
Use \fBtputs\fR to output the returned string.
The \fIarea\fP parameter is used as follows:
.RS 3
.bP
It is assumed to be the address of a pointer to a buffer managed by the
calling application.
.bP
However, ncurses checks to ensure that \fBarea\fP is not NULL,
and also that the resulting buffer pointer is not NULL.
If either check fails, the \fIarea\fP parameter is ignored.
.bP
If the checks succeed, ncurses also copies the return value to
the buffer pointed to by \fIarea\fR,
and the \fIarea\fR value will be updated to point past the null ending
this value.
.bP
The return value itself is an address in the terminal description which
is loaded into memory.
.RE
.PP
Only the first two characters of the \fBid\fR parameter of
\fBtgetflag\fR,
\fBtgetnum\fR and
\fBtgetstr\fR are compared in lookups.
.SS FORMATTING CAPABILITIES
.PP
The \fBtgoto\fR routine expands the given capability using the parameters.
.bP
Because the capability may have padding characters,
the output of \fBtgoto\fP should be passed to \fBtputs\fR
rather than some other output function such as \fBprintf\fP.
.bP
While \fBtgoto\fP is assumed to be used for the two-parameter
cursor positioning capability,
termcap applications also use it for single-parameter capabilities.
.IP
Doing this shows a quirk in \fBtgoto\fP: most hardware
terminals use cursor addressing with \fIrow\fP first,
but the original developers of the termcap interface chose to
put the \fIcolumn\fP parameter first.
The \fBtgoto\fP 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.
.bP
Normally the ncurses library is compiled with terminfo support.
In that case, \fBtgoto\fP uses \fBtparm\fP(3X) (a more capable formatter).
.IP
However, \fBtparm\fP is not a \fItermcap\fP feature,
and portable \fItermcap\fP applications should not rely upon its availability.
.PP
The \fBtputs\fR routine is described on the \fBcurs_terminfo\fR(3X) manual
page.  It can retrieve capabilities by either termcap or terminfo name.
.SS GLOBAL VARIABLES
.PP
The variables
\fBPC\fR,
\fBUP\fR and
\fBBC\fR
are set by \fBtgetent\fR to the terminfo entry's data for
\fBpad_char\fR,
\fBcursor_up\fR and
\fBbackspace_if_not_bs\fR,
respectively.
\fBUP\fR is not used by ncurses.
\fBPC\fR is used in the \fBtdelay_output\fR function.
\fBBC\fR is used in the \fBtgoto\fR emulation.
The variable \fBospeed\fR is set by ncurses in a system-specific coding
to reflect the terminal speed.
.
.SH RETURN VALUE
Except where explicitly noted,
routines that return an integer return \fBERR\fR upon failure and \fBOK\fR
(SVr4 only specifies "an integer value other than \fBERR\fR") upon successful
completion.
.PP
Routines that return pointers return \fBNULL\fR on error.
.SH BUGS
If you call \fBtgetstr\fR to fetch \fBca\fR 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 \fBtgoto\fR or \fBtparm\fR, which both expand
terminfo-style strings as terminfo.
(The \fBtgoto\fR 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).
.PP
Because terminfo conventions for representing padding in string capabilities
differ from termcap's, \fBtputs("50");\fR will put out a literal "50" rather
than busy-waiting for 50 milliseconds.  Cope with it.
.PP
Note that termcap has nothing analogous to terminfo's \fBsgr\fR string.
One consequence of this is that termcap applications assume \fRme\fR
(terminfo \fBsgr0\fR) 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.
.SH PORTABILITY
The XSI Curses standard, Issue 4 describes these functions.  However, they
are marked TO BE WITHDRAWN and may be removed in future versions.
.PP
Neither the XSI Curses standard nor the SVr4 man pages documented the return
values of \fBtgetent\fR 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 \fBtgetent\fR returns \fBOK\fR or \fBERR\fR.
Because the purpose of these functions is to provide compatibility with
the \fItermcap\fR library, that is a defect in XCurses, Issue 4, Version 2
rather than in ncurses.
.PP
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 \fBospeed\fR.
.PP
The comment that only the first two characters of the \fBid\fR 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 \fBtgetstr\fP, \fBtgetnum\fP and \fBtgetflag\fP.
Some applications assume that the termcap interface does not require
the trailing NUL for the parameter name.
Taking into account these issues:
.bP
As a special case,
\fBtgetflag\fP 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.
.bP
This implementation disallows matches by the termcap interface against
extended capability names which are longer than two characters.
.SH SEE ALSO
\fBcurses\fR(3X),
\fBterminfo\fR(\*n),
\fBterm_variables\fR(3X),
\fBputc\fR(3).
.sp
https://invisible-island.net/ncurses/tctest.html
