The curses trace routines are used for debugging the ncurses
libraries, as well as applications which use the ncurses
libraries. Some limitations apply:
• Aside from curses_trace, the other functions are normally
available only with the debugging library e.g.,
All of the trace functions may be compiled into any model
(shared, static, profile) by defining the symbol TRACE.
• Additionally, the functions which use cchar_t are only
available with the wide-character configuration of the
The principal parts of this interface are
• curses_trace, which selectively enables different tracing
• _tracef, which writes formatted data to the trace file.
The other functions either return a pointer to a string-area
(allocated by the corresponding function), or return no value
(such as _tracedump, which implements the screen dump for
TRACE_UPDATE). The caller should not free these strings,
since the allocation is reused on successive calls. To work
around the problem of a single string-area per function, some
use a buffer-number parameter, telling the library to
allocate additional string-areas.
The curses_trace function is always available, whether or not the
other trace functions are available:
• If tracing is available, calling curses_trace with a nonzero
parameter updates the trace mask, and returns the previous
When the trace mask is nonzero, ncurses creates the file
“trace” in the current directory for output. If the file
already exists, no tracing is done.
• If tracing is not available, curses_trace returns zero (0).
The trace parameter is formed by OR'ing values from the list of
TRACE_xxx definitions in <curses.h>. These include:
turn off tracing by passing a zero parameter.
The library flushes the output file, but retains an open
file-descriptor to the trace file so that it can resume
tracing later if a nonzero parameter is passed to the
trace user and system times of updates.
trace tputs(3X) calls.
trace update actions, old & new screens.
trace cursor movement and scrolling.
trace all character outputs.
trace all update actions. The old and new screen contents
are written to the trace file for each refresh.
trace all curses calls. The parameters for each call are
traced, as well as return values.
trace virtual character puts, i.e., calls to addch.
trace low-level input processing, including timeouts.
trace state of TTY control bits.
trace internal/nested calls.
trace per-character calls.
trace read/write of terminfo/termcap data.
trace changes to video attributes and colors.
maximum trace level, enables all of the separate trace
Some tracing features are enabled whenever the curses_trace
parameter is nonzero. Some features overlap. The specific names
are used as a guideline.
These functions check the NCURSES_TRACE environment variable, to
set the tracing feature as if curses_trace was called:
filter, initscr, new_prescr, newterm, nofilter, restartterm,
ripoffline, setupterm, slk_init, tgetent, use_env,
The command-line utilities such as tic(1) provide a verbose
option which extends the set of messages written using the
curses_trace function. Both of these (-v and curses_trace) use
the same variable (_nc_tracing), which determines the messages
which are written.
Because the command-line utilities may call initialization
functions such as setupterm, tgetent or use_extended_names, some
of their debugging output may be directed to the trace file if
the NCURSES_TRACE environment variable is set:
• messages produced in the utility are written to the standard
• messages produced by the underlying library are written to
If ncurses is built without tracing, none of the latter are
produced, and fewer diagnostics are provided by the command-line
These functions are not part of the XSI interface. Some other
curses implementations are known to have similar features, but
they are not compatible with ncurses:
• SVr4 provided traceon and traceoff, to control whether
debugging information was written to the “trace” file. While
the functions were always available, this feature was only
enabled if DEBUG was defined when building the library.
The SVr4 tracing feature is undocumented.
• PDCurses provides traceon and traceoff, which (like SVr4) are
always available, and enable tracing to the “trace” file only
when a debug-library is built.
PDCurses has a short description of these functions, with a
note that they are not present in X/Open Curses, ncurses or
NetBSD. It does not mention SVr4, but the functions'
inclusion in a header file section labeled “Quasi-standard”
hints at the origin.
• NetBSD does not provide functions for enabling/disabling
traces. It uses environment variables CURSES_TRACE_MASK and
CURSES_TRACE_FILE to determine what is traced, and where the
results are written. This is available only when a debug-
library is built.
The NetBSD tracing feature is undocumented.
A few ncurses functions are not provided when symbol versioning
_nc_tracebits, _tracedump, _tracemouse
The original trace routine was deprecated because it often
conflicted with application names.
This page is part of the ncurses (new curses) project.
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