man/curs_initscr.3x

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.\" $Id: curs_initscr.3x,v 1.69 2024/04/20 21:24:19 tom Exp $
.TH curs_initscr 3X 2024-04-20 "ncurses @NCURSES_MAJOR@.@NCURSES_MINOR@" "Library calls"
.ie \n(.g \{\
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.de bP
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..
.SH NAME
\fB\%initscr\fP,
\fB\%newterm\fP,
\fB\%endwin\fP,
\fB\%isendwin\fP,
\fB\%set_term\fP,
\fB\%delscreen\fP \-
initialize, manipulate, or tear down \fIcurses\fR terminal interface
.SH SYNOPSIS
.nf
\fB#include <curses.h>
.PP
\fBWINDOW *initscr(void);
\fBint endwin(void);
.PP
\fBbool isendwin(void);
.PP
\fBSCREEN *newterm(const char *\fItype\fP, FILE *\fIoutf\fP, FILE *\fIinf\fP);
\fBSCREEN *set_term(SCREEN *\fInew\fP);
\fBvoid delscreen(SCREEN* \fIsp\fP);
.fi
.SH DESCRIPTION
.SS initscr
\fBinitscr\fP is normally the first \fBcurses\fP routine to call when
initializing a program.
A few special routines sometimes need to be called before it;
these are \fBslk_init\fP(3X), \fBfilter\fP, \fBripoffline\fP,
\fBuse_env\fP.
For multiple-terminal applications,
\fBnewterm\fP may be called before \fBinitscr\fP.
.PP
The initscr code determines the terminal type and initializes all \fBcurses\fP
data structures.
\fBinitscr\fP also causes the first call to \fBrefresh\fP(3X)
to clear the screen.
If errors occur, \fBinitscr\fP writes an appropriate error
message to standard error and exits;
otherwise, a pointer is returned to \fBstdscr\fP.
.SS newterm
A program that outputs to more than one terminal should use the \fBnewterm\fP
routine for each terminal instead of \fBinitscr\fP.
A program that needs to inspect capabilities,
so it can continue to run in a line-oriented mode if the
terminal cannot support a screen-oriented program, would also use
\fBnewterm\fP.
.PP
The routine \fBnewterm\fP should be called once for each terminal.
It returns a variable of type \fISCREEN *\fP which should be saved
as a reference to that terminal.
\fBnewterm\fP's arguments are
.bP
the \fItype\fP of the terminal to be used in place of \fB$TERM\fP,
.bP
an output stream connected to the terminal, and
.bP
an input stream connected to the terminal
.PP
If the \fItype\fP parameter is \fBNULL\fP, \fB$TERM\fP will be used.
.PP
The file descriptor of the output stream is passed to \fBsetupterm\fP(3X),
which returns a pointer to a \fI\%TERMINAL\fP structure.
\fBnewterm\fP's return value holds a pointer to the \fI\%TERMINAL\fP structure.
.SS endwin
The program must also call
\fBendwin\fP for each terminal being used before exiting from \fBcurses\fP.
If \fBnewterm\fP is called more than once for the same terminal, the first
terminal referred to must be the last one for which \fBendwin\fP is called.
.PP
A program should always call \fBendwin\fP before exiting or escaping from
\fBcurses\fP mode temporarily.
This routine
.bP
resets colors to correspond with the default color pair 0,
.bP
moves the cursor to the lower left-hand corner of the screen,
.bP
clears the remainder of the line so that it uses the default colors,
.bP
sets the cursor to normal visibility (see \fBcurs_set\fP(3X)),
.bP
stops cursor-addressing mode using the \fIexit_ca_mode\fP terminal capability,
.bP
restores tty modes (see \fBreset_shell_mode\fP(3X)).
.PP
Calling \fBrefresh\fP(3X) or \fBdoupdate\fP(3X) after a
temporary escape causes the program to resume visual mode.
.SS isendwin
The \fBisendwin\fP routine returns \fBTRUE\fP if \fBendwin\fP has been
called without any subsequent calls to \fBwrefresh\fP,
and \fBFALSE\fP otherwise.
.SS set_term
The \fBset_term\fP routine is used to switch between different terminals.
The screen reference \fInew\fP becomes the new current terminal.
The previous terminal is returned by the routine.
This is the only routine which manipulates \fISCREEN\fP pointers;
all other routines affect only the current terminal.
.SS delscreen
The \fBdelscreen\fP routine frees storage associated with the
\fISCREEN\fP data structure.
The \fBendwin\fP routine does not do
this, so \fBdelscreen\fP should be called after \fBendwin\fP if a
particular \fISCREEN\fP is no longer needed.
.SH RETURN VALUE
\fBendwin\fP returns the integer \fBERR\fP upon failure and \fBOK\fP
upon successful completion.
.PP
Routines that return pointers always return \fBNULL\fP on error.
.PP
X/Open defines no error conditions.
In this implementation
.bP
\fBendwin\fP returns an error if
.RS
.bP
the terminal was not initialized, or
.bP
\fBendwin\fP is called more than once without updating the screen, or
.bP
\fBreset_shell_mode\fP(3X) returns an error.
.RE
.bP
\fBnewterm\fP
returns an error if it cannot allocate the data structures for the screen,
or for the top-level windows within the screen,
i.e.,
\fBcurscr\fP, \fBnewscr\fP, or \fBstdscr\fP.
.bP
\fBset_term\fP
returns no error.
.SH PORTABILITY
These functions were described in X/Open Curses, Issue 4.
As of 2015, the current document is X/Open Curses, Issue 7.
.SS Differences
X/Open Curses specifies that portable applications must not
call \fBinitscr\fP more than once:
.bP
The portable way to use \fBinitscr\fP is once only,
using \fB\%refresh\fP(3X)
to restore the screen after \fBendwin\fP.
.bP
This implementation allows using \fBinitscr\fP after \fBendwin\fP.
.PP
Old versions of curses, e.g., BSD 4.4, would return a null pointer
from \fBinitscr\fP when an error is detected, rather than exiting.
It is safe but redundant to check the return value of \fBinitscr\fP
in X/Open Curses.
.PP
Calling \fBendwin\fP does not dispose of the memory allocated in \fBinitscr\fP
or \fBnewterm\fP.
Deleting a \fISCREEN\fP provides a way to do this:
.bP
X/Open Curses does not say what happens to \fI\%WINDOW\fPs when \fBdelscreen\fP
\*(``frees storage associated with the \fISCREEN\fP\*(''
nor does the SVr4 documentation help,
adding that it should be called after \fBendwin\fP if a \fISCREEN\fP
is no longer needed.
.bP
However, \fI\%WINDOW\fPs are implicitly associated with a \fISCREEN\fP.
so that it is reasonable to expect \fBdelscreen\fP to deal with these.
.bP
SVr4 curses deletes the standard \fI\%WINDOW\fP structures
\fBstdscr\fP and \fBcurscr\fP as well as a work area \fBnewscr\fP.
SVr4 curses ignores other windows.
.bP
Since version 4.0 (1996),
\fI\%ncurses\fP has maintained a list of all windows for each screen,
using that information to delete those windows when \fBdelscreen\fP is called.
.bP
NetBSD copied this feature of \fI\%ncurses\fP in 2001.
PDCurses follows the SVr4 model,
deleting only the standard \fI\%WINDOW\fP structures.
.SS "High-level versus Low-level"
Different implementations may disagree regarding the level of some functions.
For example, \fISCREEN\fP (returned by \fBnewterm\fP) and
\fI\%TERMINAL\fP (returned by \fBsetupterm\fP(3X)) hold file descriptors for
the output stream.
If an application switches screens using \fBset_term\fR,
or switches terminals using \fBset_curterm\fP(3X),
applications which use the output file descriptor can have different
behavior depending on which structure holds the corresponding descriptor.
.PP
For example
.bP
NetBSD's \fBbaudrate\fP(3X) function uses the descriptor in \fI\%TERMINAL\fP.
\fI\%ncurses\fP and SVr4 use the descriptor in \fISCREEN\fP.
.bP
NetBSD and \fI\%ncurses\fP use the descriptor
in \fI\%TERMINAL\fP
for terminal I/O modes,
e.g.,
\fBdef_shell_mode\fP(3X),
\fBdef_prog_mode\fP(3X).
SVr4 curses uses the descriptor in \fISCREEN\fP.
.SS "Unset \fITERM\fP Variable"
If the \fITERM\fP variable is missing or empty, \fBinitscr\fP uses the
value \*(``unknown\*('',
which normally corresponds to a terminal entry with the \fIgeneric\fP
(\fIgn\fP) capability.
Generic entries are detected by \fBsetupterm\fP(3X)
and cannot be used for full-screen operation.
Other implementations may handle
a missing/empty \fITERM\fP variable differently.
.SS "Signal Handlers"
Quoting from X/Open Curses Issue 7, section 3.1.1:
.RS 5
.PP
Curses implementations may provide for special handling of the
\%SIGINT,
\%SIGQUIT,
and \%SIGTSTP signals if their disposition is \%SIG_DFL at the time
.I \%initscr
is called.\|.\|.
.PP
Any special handling for these signals may remain in effect for the
life of the process or until the process changes the disposition of
the signal.
.PP
None of the Curses functions are required to be safe
with respect to signals.\|.\|.
.RE
.PP
This implementation establishes signal handlers during initialization,
e.g., \fBinitscr\fP or \fBnewterm\fP.
Applications which must handle these signals should set up the corresponding
handlers \fIafter\fP initializing the library:
.TP 5
.B SIGINT
The handler \fIattempts\fP to clean up the screen on exit.
Although it \fIusually\fP works as expected, there are limitations:
.RS 5
.bP
Walking the \fISCREEN\fP list is unsafe, since all list management
is done without any signal blocking.
.bP
On systems which have \fBREENTRANT\fP turned on, \fBset_term\fP uses
functions which could deadlock or misbehave in other ways.
.bP
\fBendwin\fP calls other functions,
many of which use \fI\%stdio\fP(3) or other library functions which are
clearly unsafe.
.RE
.TP 5
.B SIGTERM
This uses the same handler as \fBSIGINT\fP, with the same limitations.
It is not mentioned in X/Open Curses, but is more suitable for this
purpose than \fBSIGQUIT\fP (which is used in debugging).
.TP 5
.B SIGTSTP
This handles the \fIstop\fP signal, used in job control.
When resuming the process, this implementation discards pending
input with \fB\%flushinp\fP(3X), and repaints the screen
assuming that it has been completely altered.
It also updates the saved terminal modes with
\fB\%def_shell_mode\fP(3X).
.TP 5
.B SIGWINCH
This handles the window-size changes which were ignored in
the standardization efforts.
The handler sets a (signal-safe) variable
which is later tested in \fB\%wgetch\fP(3X).
If \fBkeypad\fP has been enabled for the corresponding window,
\fBwgetch\fP returns the key symbol \fBKEY_RESIZE\fP.
At the same time, \fBwgetch\fP calls \fBresizeterm\fP to adjust the
standard screen \fBstdscr\fP,
and update other data such as \fBLINES\fP and \fBCOLS\fP.
.SH SEE ALSO
\fB\%curses\fP(3X),
\fB\%curs_kernel\fP(3X),
\fB\%curs_refresh\fP(3X),
\fB\%curs_slk\fP(3X),
\fB\%curs_terminfo\fP(3X),
\fB\%curs_util\fP(3X),
\fB\%curs_variables\fP(3X)