System V curses implementations can support BSD curses programs with just a recompilation, so by capturing the System V API we also capture BSD's.
More importantly for the future, the XSI Curses standard issued by X/Open is explicitly and closely modeled on System V. So conformance with System V took us most of the way to base-level XSI conformance.
Accordingly, we have a policy of associating with each nonstandard extension a feature macro, so that ncurses client code can use this macro to condition in or out the code that requires the ncurses extension.
For example, there is a macro
NCURSES_MOUSE_VERSION which XSI Curses
does not define, but which is defined in the ncurses library header.
You can use this to condition the calls to the mouse API calls.
We encourage (but do not require) developers to make the code friendly to less-capable UNIX environments wherever possible.
We encourage developers to support OS-specific optimizations and methods not available under POSIX/ANSI, provided only that:
autoconf(1)as a tool to deal with portability issues. The right way to leverage an OS-specific feature is to modify the autoconf specification files (configure.in and aclocal.m4) to set up a new feature macro, which you then use to condition your code.
The reason for choosing HTML is that it's (a) well-adapted for on-line browsing through viewers that are everywhere; (b) more easily readable as plain text than most other mark-ups, if you don't have a viewer; and (c) carries enough information that you can generate a nice-looking printed version from it. Also, of course, it make exporting things like the announcement document to WWW pretty trivial.
email@example.com a message containing the line:
ncursescode is maintained by a small group of volunteers. While we try our best to fix bugs promptly, we simply don't have a lot of hours to spend on elementary hand-holding. We rely on intelligent cooperation from our users. If you think you have found a bug in
ncurses, there are some steps you can take before contacting us that will help get the bug fixed quickly.
In order to use our bug-fixing time efficiently, we put people who show us they've taken these steps at the head of our queue. This means that if you don't, you'll probably end up at the tail end and have to wait a while.
Bugs we can reproduce are likely to be fixed very quickly, often within days. The most effective single thing you can do to get a quick fix is develop a way we can duplicate the bad behavior -- ideally, by giving us source for a small, portable test program that breaks the library. (Even better is a keystroke recipe using one of the test programs provided with the distribution.)
In our experience, most of the behaviors people report as library bugs are actually due to subtle problems in terminal descriptions. This is especially likely to be true if you're using a traditional asynchronous terminal or PC-based terminal emulator, rather than xterm or a UNIX console entry.
It's therefore extremely helpful if you can tell us whether or not your problem reproduces on other terminal types. Usually you'll have both a console type and xterm available; please tell us whether or not your bug reproduces on both.
If you have xterm available, it is also good to collect xterm reports for different window sizes. This is especially true if you normally use an unusual xterm window size -- a surprising number of the bugs we've seen are either triggered or masked by these.
Recompile your program with the debugging versions of the libraries.
trace() call with the argument set to
(See "Writing Programs with
NCURSES" for details on trace levels.)
Reproduce your bug, then look at the trace file to see what the library
was actually doing.
Another frequent cause of apparent bugs is application coding errors that cause the wrong things to be put on the virtual screen. Looking at the virtual-screen dumps in the trace file will tell you immediately if this is happening, and save you from the possible embarrassment of being told that the bug is in your code and is your problem rather than ours.
If the virtual-screen dumps look correct but the bug persists, it's possible to crank up the trace level to give more and more information about the library's update actions and the control sequences it issues to perform them. The test directory of the distribution contains a tool for digesting these logs to make them less tedious to wade through.
Often you'll find terminfo problems at this stage by noticing that the escape sequences put out for various capabilities are wrong. If not, you're likely to learn enough to be able to characterize any bug in the screen-update logic quite exactly.
If you do the preceding two steps, it is very likely that you'll discover the nature of the problem yourself and be able to send us a fix. This will create happy feelings all around and earn you good karma for the first time you run into a bug you really can't characterize and fix yourself.
If you're still stuck, at least you'll know what to tell us. Remember, we need details. If you guess about what is safe to leave out, you are too likely to be wrong.
If your bug produces a bad update, include a trace file. Try to make the trace at the least voluminous level that pins down the bug. Logs that have been through tracemunch are OK, it doesn't throw away any information (actually they're better than un-munched ones because they're easier to read).
If your bug produces a core-dump, please include a symbolic stack trace generated by gdb(1) or your local equivalent.
Tell us about every terminal on which you've reproduced the bug -- and every terminal on which you can't. Ideally, sent us terminfo sources for all of these (yours might differ from ours).
Include your ncurses version and your OS/machine type, of course! You can
find your ncurses version in the
The most important of these is
mvcur, a test frame for the
cursor-movement optimization code. With this program, you can see
directly what control sequences will be emitted for any given cursor
movement or scroll/insert/delete operations. If you think you've got
a bad capability identified, you can disable it and test again. The
program is command-driven and has on-line help.
If you think the vertical-scroll optimization is broken, or just want to
understand how it works better, build
hashmap and read the
header comments of
hashmap.c; then try
it out. You can also test the hardware-scrolling optimization separately
are all in this category. They are very unlikely to need change, barring bugs or some fundamental reorganization in the underlying data structures.
lib_addch.c lib_bkgd.c lib_box.c lib_chgat.c lib_clear.c lib_clearok.c lib_clrbot.c lib_clreol.c lib_colorset.c lib_data.c lib_delch.c lib_delwin.c lib_echo.c lib_erase.c lib_gen.c lib_getstr.c lib_hline.c lib_immedok.c lib_inchstr.c lib_insch.c lib_insdel.c lib_insstr.c lib_instr.c lib_isendwin.c lib_keyname.c lib_leaveok.c lib_move.c lib_mvwin.c lib_overlay.c lib_pad.c lib_printw.c lib_redrawln.c lib_scanw.c lib_screen.c lib_scroll.c lib_scrollok.c lib_scrreg.c lib_set_term.c lib_slk.c lib_slkatr_set.c lib_slkatrof.c lib_slkatron.c lib_slkatrset.c lib_slkattr.c lib_slkclear.c lib_slkcolor.c lib_slkinit.c lib_slklab.c lib_slkrefr.c lib_slkset.c lib_slktouch.c lib_touch.c lib_unctrl.c lib_vline.c lib_wattroff.c lib_wattron.c lib_window.c
These files are used only for debugging support:
It is rather unlikely you will ever need to change these, unless you want to introduce a new debug trace level for some reason.
lib_trace.c lib_traceatr.c lib_tracebits.c lib_tracechr.c lib_tracedmp.c lib_tracemse.c trace_buf.c
There is another group of files that do direct I/O via tputs(), computations on the terminal capabilities, or queries to the OS environment, but nevertheless have only fairly low complexity. These include:
They are likely to need revision only if ncurses is being ported to an environment without an underlying terminfo capability representation.
lib_acs.c lib_beep.c lib_color.c lib_endwin.c lib_initscr.c lib_longname.c lib_newterm.c lib_options.c lib_termcap.c lib_ti.c lib_tparm.c lib_tputs.c lib_vidattr.c read_entry.c.
These files have serious hooks into the tty driver and signal facilities:
If you run into porting snafus moving the package to another UNIX, the problem is likely to be in one of these files. The file
lib_kernel.c lib_baudrate.c lib_raw.c lib_tstp.c lib_twait.c
lib_print.cuses sleep(2) and also falls in this category.
Almost all of the real work is done in the files
Most of the algorithmic complexity in the library lives in these files. If there is a real bug in ncurses itself, it's probably here. We'll tour some of these files in detail below (see The Engine Room).
hardscroll.c hashmap.c lib_addch.c lib_doupdate.c lib_getch.c lib_mouse.c lib_mvcur.c lib_refresh.c lib_setup.c lib_vidattr.c
Finally, there is a group of files that is actually most of the terminfo compiler. The reason this code lives in the ncurses library is to support fallback to /etc/termcap. These files include
We'll discuss these in the compiler tour.
alloc_entry.c captoinfo.c comp_captab.c comp_error.c comp_hash.c comp_parse.c comp_scan.c parse_entry.c read_termcap.c write_entry.c
ncursesinput funnels through the function
wgetch(), defined in
lib_getch.c. This function is tricky; it has to poll for keyboard and mouse events and do a running match of incoming input against the set of defined special keys.
The central data structure in this module is a FIFO queue, used to
match multiple-character input sequences against special-key
capabilities; also to implement pushback via
wgetch() code distinguishes between function key
sequences and the same sequences typed manually by doing a timed wait
after each input character that could lead a function key sequence.
If the entire sequence takes less than 1 second, it is assumed to have
been generated by a function key press.
Hackers bruised by previous encounters with variant
calls may find the code in
lib_twait.c interesting. It deals
with the problem that some BSD selects don't return a reliable
time-left value. The function
simulates a System V select.
wgetch()polls for mouse events each call, before it goes to the keyboard for input. It is up to
lib_mouse.chow the polling is accomplished; it may vary for different devices.
Under xterm, however, mouse event notifications come in via the keyboard input stream. They are recognized by having the kmous capability as a prefix. This is kind of klugey, but trying to wire in recognition of a mouse key prefix without going through the function-key machinery would be just too painful, and this turns out to imply having the prefix somewhere in the function-key capabilities at terminal-type initialization.
This kluge only works because kmous isn't actually used by any historic terminal type or curses implementation we know of. Best guess is it's a relic of some forgotten experiment in-house at Bell Labs that didn't leave any traces in the publicly-distributed System V terminfo files. If System V or XPG4 ever gets serious about using it again, this kluge may have to change.
Here are some more details about mouse event handling:
lib_mouse()code is logically split into a lower level that
accepts event reports in a device-dependent format and an upper level that
parses mouse gestures and filters events. The mediating data structure is a
circular queue of event structures.
Functionally, the lower level's job is to pick up primitive events and
put them on the circular queue. This can happen in one of two ways:
_nc_mouse_event() detects a series of incoming
mouse reports and queues them, or (b) code in
lib_getch.c detects the
kmous prefix in the keyboard input stream and calls _nc_mouse_inline
to queue up a series of adjacent mouse reports.
In either case,
_nc_mouse_parse() should be called after the
series is accepted to parse the digested mouse reports (low-level
events) into a gesture (a high-level or composite event).
wgetnstr()call (which simulates cooked-mode line editing in an ncurses window), the library normally does all its output at refresh time.
The main job is to go from the current state of the screen (as represented
curscr window structure) to the desired new state (as
represented in the
newscr window structure), while doing as
little I/O as possible.
The brains of this operation are the modules
lib_doupdate.c; the latter two use
lib_mvcur.c. Essentially, what happens looks like this:
hashmap.c module tries to detect vertical motion
changes between the real and virtual screens. This information
is represented by the oldindex members in the newscr structure.
These are modified by vertical-motion and clear operations, and both are
re-initialized after each update. To this change-journalling
information, the hashmap code adds deductions made using a modified Heckel
algorithm on hash values generated from the line contents.
hardscroll.c module computes an optimum set of scroll,
insertion, and deletion operations to make the indices match. It calls
lib_mvcur.c to do those motions.
lib_doupdate.c goes to work. Its job is to do line-by-line
curscr lines to
newscr lines. Its main
tool is the routine
lib_mvcur.c. This routine
does cursor-movement optimization, attempting to get from given screen
location A to given location B in the fewest output characters possible.
If you want to work on screen optimizations, you should use the fact
that (in the trace-enabled version of the library) enabling the
TRACE_TIMES trace level causes a report to be emitted after
each screen update giving the elapsed time and a count of characters
emitted during the update. You can use this to tell when an update
optimization improves efficiency.
In the trace-enabled version of the library, it is also possible to disable
and re-enable various optimizations at runtime by tweaking the variable
_nc_optimize_enable. See the file
for mask values, near the end.
The configuration code prefers the POSIX regex facility, modeled on System V's, but will settle for BSD regexps if the former isn't available.
Historical note: the panels code was written primarily to assist in
porting u386mon 2.0 (comp.sources.misc v14i001-4) to systems lacking
panels support; u386mon 2.10 and beyond use it. This version has been
slightly cleaned up for
The implementation therefore starts with a table-driven, dual-mode
lexical analyzer (in
comp_scan.c). The lexer chooses its
mode (termcap or terminfo) based on the first `,' or `:' it finds in
each entry. The lexer does all the work of recognizing capability
names and values; the grammar above it is trivial, just "parse entries
till you run out of file".
One possibly interesting aspect of the implementation is the way the
compiler tables are initialized. All the tables are generated by various
awk/sed/sh scripts from a master table
scripts actually write C initializers which are linked to the compiler.
Furthermore, the hash table is generated in the same way, so it doesn't
have to be generated at compiler startup time (another benefit of this
organization is that the hash table can be in shareable text space).
Thus, adding a new capability is usually pretty trivial, just a matter
of adding one line to the
include/Caps file. We'll have more
to say about this in the section on Source-Form
This won't do for ncurses. The problem is that that the whole compilation process has to be embeddable in the ncurses library so that it can be called by the startup code to translate termcap entries on the fly. The embedded version can't go promiscuously writing everything it translates out to disk -- for one thing, it will typically be running with non-root permissions.
So our tic is designed to parse an entire terminfo file into a doubly-linked circular list of entry structures in-core, and then do use resolution in-memory before writing everything out. This design has other advantages: it makes forward and back use-references equally easy (so we get the latter for free), and it makes checking for name collisions before they're written out easy to do.
And this is exactly how the embedded version works. But the stand-alone user-accessible version of tic partly reverts to the historical strategy; it writes to disk (not keeping in core) any entry with no use references.
This is strictly a core-economy kluge, implemented because the terminfo master file is large enough that some core-poor systems swap like crazy when you compile it all in memory...there have been reports of this process taking three hours, rather than the twenty seconds or less typical on the author's development box.
So. The executable tic passes the entry-parser a hook that immediately writes out the referenced entry if it has no use capabilities. The compiler main loop refrains from adding the entry to the in-core list when this hook fires. If some other entry later needs to reference an entry that got written immediately, that's OK; the resolution code will fetch it off disk when it can't find it in core.
Name collisions will still be detected, just not as cleanly. The
write_entry() code complains before overwriting an entry that
postdates the time of tic's first call to
write_entry(), Thus it will complain about overwriting
entries newly made during the tic run, but not about
overwriting ones that predate it.
The translation output code (
ncurses/dump_entry.c) is shared with the infocmp(1)
utility. It takes the same internal representation used to generate
the binary form and dumps it to standard output in a specified
include/Caps file has a header comment describing ways you
can specify source translations for nonstandard capabilities just by
altering the master table. It's possible to set up capability aliasing
or tell the compiler to plain ignore a given capability without writing
any C code at all.
For circumstances where you need to do algorithmic translation, there
are functions in
parse_entry.c called after the parse of each
entry that are specifically intended to encapsulate such
translations. This, for example, is where the AIX box1 capability
get translated to an acsc string.
dump_entry()to control which capabilities are dumped. This is necessary in order to handle both the ordinary De-compilation case and entry difference reporting.
The tput and clear utilities just do an entry load
followed by a
tputs() of a selected capability.
_nc_ should be used on library public functions that are
not part of the curses API in order to prevent pollution of the
If you have to add to or modify the function prototypes in curses.h.in,
read ncurses/MKlib_gen.sh first so you can avoid breaking XSI conformance.
Please join the ncurses mailing list. See the INSTALL file in the
top level of the distribution for details on the list.
Look for the string
FIXME in source files to tag minor bugs
and potential problems that could use fixing.
Don't try to auto-detect OS features in the main body of the C code. That's the job of the configuration system.
To hold down complexity, do make your code data-driven. Especially,
if you can drive logic from a table filtered out of
include/Caps, do it. If you find you need to augment the
data in that file in order to generate the proper table, that's still
preferable to ad-hoc code -- that's why the fifth field (flags) is
The following library modules are `pure curses'; they operate only on
the curses internal structures, do all output through other curses
calls (not including
putp()) and do not
call any other UNIX routines such as signal(2) or the stdio library.
Thus, they should not need to be modified for single-terminal
lib_addch.c lib_addstr.c lib_bkgd.c lib_box.c lib_clear.c lib_clrbot.c lib_clreol.c lib_delch.c lib_delwin.c lib_erase.c lib_inchstr.c lib_insch.c lib_insdel.c lib_insstr.c lib_keyname.c lib_move.c lib_mvwin.c lib_newwin.c lib_overlay.c lib_pad.c lib_printw.c lib_refresh.c lib_scanw.c lib_scroll.c lib_scrreg.c lib_set_term.c lib_touch.c lib_tparm.c lib_tputs.c lib_unctrl.c lib_window.c panel.c
This module is pure curses, but calls outstr():
These modules are pure curses, except that they use
lib_beep.c lib_color.c lib_endwin.c lib_options.c lib_slk.c lib_vidattr.c
This modules assist in POSIX emulation on non-POSIX systems:
alloc_entry.c captoinfo.c clear.c comp_captab.c comp_error.c comp_hash.c comp_main.c comp_parse.c comp_scan.c dump_entry.c infocmp.c parse_entry.c read_entry.c tput.c write_entry.c
The following modules will use open()/read()/write()/close()/lseek() on files, but no other OS calls.
The following modules are `pure curses' but contain assumptions inappropriate for a memory-mapped port.