The trace routines are used for debugging the ncurses libraries, as
well as applications which use the ncurses libraries. These
functions are normally available only with the debugging library
e.g., libncurses_g.a, but may be compiled into any model (shared,
static, profile) by defining the symbol TRACE. Additionally, some
functions are only available with the wide-character configuration of
The principal parts of this interface are
· trace, which selectively enables different tracing features, and
· _tracef, which writes formatted data to the trace file.
Calling trace with a nonzero parameter creates the file trace in the
current directory for output. If the file already exists, no tracing
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 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 function.
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 features.
Some tracing features are enabled whenever the trace parameter is
nonzero. Some features overlap. The specific names are used as a
These functions check the NCURSES_TRACE environment variable, to set
the tracing feature as if 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 trace function.
Both of these (-v and 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 de‐
bugging 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 er‐
· messages produced by the underlying library are written to trace.
If ncurses is built without tracing, none of the latter are produced,
and fewer diagnostics are provided by the command-line utilities.
These functions are not part of the XSI interface. Some other curses
implementations are known to have similar, undocumented features, but
they are not compatible with ncurses.
A few functions are not provided when symbol versioning is used:
_nc_tracebits, _tracedump, _tracemouse
This page is part of the ncurses (new curses) project. Information
about the project can be found at
⟨https://www.gnu.org/software/ncurses/ncurses.html⟩. If you have a
bug report for this manual page, send it to
email@example.com. This page was obtained from the
project's upstream Git mirror of the CVS repository
⟨git://ncurses.scripts.mit.edu/ncurses.git⟩ on 2017-03-13. If you
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you believe there is a better or more up-to-date source for the page,
or you have corrections or improvements to the information in this
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