(octave.info)Breakpoints
13.3 Breakpoints
================
Breakpoints can be set in any m-file function by using the ‘dbstop’
function.
-- : dbstop FUNC
-- : dbstop FUNC LINE
-- : dbstop FUNC LINE1 LINE2 ...
-- : dbstop LINE1 ...
-- : dbstop in FUNC
-- : dbstop in FUNC at LINE
-- : dbstop in FUNC at LINE if "CONDITION"
-- : dbstop if EVENT
-- : dbstop if EVENT ID
-- : dbstop (BP_STRUCT)
-- : RLINE = dbstop ...
Set breakpoints for the built-in debugger.
FUNC is the name of a function on the current ‘path’. When already
in debug mode the FUNC argument can be omitted and the current
function will be used. Breakpoints at subfunctions are set with
the scope operator ‘>’. For example, If ‘file.m’ has a subfunction
‘func2’, then a breakpoint in ‘func2’ can be specified by
‘file>func2’.
LINE is the line number at which to break. If LINE is not
specified, it defaults to the first executable line in the file
‘func.m’. Multiple lines can be specified in a single command;
when function syntax is used, the lines may also be passed as a
single vector argument (‘[LINE1, LINE2, ...]’).
CONDITION is any Octave expression that can be evaluated in the
code context that exists at the breakpoint. When the breakpoint is
encountered, CONDITION will be evaluated, and execution will stop
if CONDITION is true. If CONDITION cannot be evaluated, for
example because it refers to an undefined variable, an error will
be thrown. Expressions with side effects (such as ‘y++ > 1’) will
alter variables, and should generally be avoided. Conditions
containing quotes (‘"’, ‘'’) or comment characters (‘#’, ‘%’) must
be enclosed in quotes. (This does not apply to conditions entered
from the editor’s context menu.) For example:
dbstop in strread at 209 if 'any (format == "%f")'
The form specifying EVENT does not cause a specific breakpoint at a
given function and line number. Instead it causes debug mode to be
entered when certain unexpected events are encountered. Possible
values are
‘error’
Stop when an error is reported. This is equivalent to
specifying both ‘debug_on_error (true)’ and
‘debug_on_interrupt (true)’.
‘caught error’
Stop when an error is caught by a try-catch block (not yet
implemented).
‘interrupt’
Stop when an interrupt (‘Ctrl-C’) occurs.
‘naninf’
Stop when code returns a non-finite value (not yet
implemented).
‘warning’
Stop when a warning is reported. This is equivalent to
specifying ‘debug_on_warning (true)’.
The events ‘error’, ‘caught error’, and ‘warning’ can all be
followed by a string specifying an error ID or warning ID. If that
is done, only errors with the specified ID will cause execution to
stop. To stop on one of a set of IDs, multiple ‘dbstop’ commands
must be issued.
Breakpoints and events can be removed using the ‘dbclear’ command
with the same syntax.
It is possible to save all breakpoints and restore them at once by
issuing the commands ‘bp_state = dbstatus; ...; dbstop (bp_state)’.
The optional output RLINE is the real line number where the
breakpoint was set. This can differ from the specified line if the
line is not executable. For example, if a breakpoint attempted on
a blank line then Octave will set the real breakpoint at the next
executable line.
When a file is re-parsed, such as when it is modified outside the
GUI, all breakpoints within the file are cleared.
See also: Note: dbclear, Note: dbstatus,
Note: dbstep, Note: debug_on_error,
Note: debug_on_warning, Note:
debug_on_interrupt.
Breakpoints in class methods are also supported (e.g., ‘dbstop
("@class/method")’). However, breakpoints cannot be set in built-in
functions (e.g., ‘sin’, etc.) or dynamically loaded functions (i.e.,
oct-files).
To set a breakpoint immediately upon entering a function use line
number 1, or omit the line number entirely and just give the function
name. When setting the breakpoint Octave will ignore the leading
comment block, and the breakpoint will be set on the first executable
statement in the function. For example:
dbstop ("asind", 1)
⇒ 29
Note that the return value of ‘29’ means that the breakpoint was
effectively set to line 29. The status of breakpoints in a function can
be queried with ‘dbstatus’.
-- : dbstatus
-- : dbstatus FUNC
-- : BP_LIST = dbstatus ...
Report the location of active breakpoints.
When called with no input or output arguments, print the list of
all functions with breakpoints and the line numbers where those
breakpoints are set.
If a function name FUNC is specified then only report breakpoints
for the named function and its subfunctions.
The optional return argument BP_LIST is a struct array with the
following fields.
name
The name of the function with a breakpoint. A subfunction,
say ‘func2’ within an m-file, say ‘file.m’, is specified as
‘file>func2’.
file
The name of the m-file where the function code is located.
line
The line number with the breakpoint.
cond
The condition that must be satisfied for the breakpoint to be
active, or the empty string for unconditional breakpoints.
If ‘dbstop if error’ is true but no explicit IDs are specified, the
return value will have an empty field called "errs". If IDs are
specified, the ‘errs’ field will have one row per ID. If ‘dbstop
if error’ is false, there is no "errs" field. The "warn" field is
set similarly by ‘dbstop if warning’.
See also: Note: dbstop, Note: dbclear,
Note: dbwhere, Note: dblist, Note:
dbstack.
Reusing the previous example, ‘dbstatus ("asind")’ will return 29. The
breakpoints listed can then be cleared with the ‘dbclear’ function.
-- : dbclear FUNC
-- : dbclear FUNC LINE
-- : dbclear FUNC LINE1 LINE2 ...
-- : dbclear LINE ...
-- : dbclear all
-- : dbclear in FUNC
-- : dbclear in FUNC at LINE
-- : dbclear if EVENT
-- : dbclear ("FUNC")
-- : dbclear ("FUNC", LINE)
-- : dbclear ("FUNC", LINE1, LINE2, ...)
-- : dbclear ("FUNC", LINE1, ...)
-- : dbclear (LINE, ...)
-- : dbclear ("all")
Delete a breakpoint at line number LINE in the function FUNC.
Arguments are
FUNC
Function name as a string variable. When already in debug
mode this argument can be omitted and the current function
will be used.
LINE
Line number from which to remove a breakpoint. Multiple lines
may be given as separate arguments or as a vector.
EVENT
An event such as ‘error’, ‘interrupt’, or ‘warning’ (Note:
dbstop. for details).
When called without a line number specification all breakpoints in
the named function are cleared.
If the requested line is not a breakpoint no action is performed.
The special keyword "all" will clear all breakpoints from all
files.
See also: Note: dbstop, Note: dbstatus,
Note: dbwhere.
A breakpoint may also be set in a subfunction. For example, if a
file contains the functions
function y = func1 (x)
y = func2 (x);
endfunction
function y = func2 (x)
y = x + 1;
endfunction
then a breakpoint can be set at the start of the subfunction directly
with
dbstop func1>func2
⇒ 5
Note that ‘>’ is the character that distinguishes subfunctions from
the m-file containing them.
Another simple way of setting a breakpoint in an Octave script is the
use of the ‘keyboard’ function.
-- : keyboard ()
-- : keyboard ("PROMPT")
Stop m-file execution and enter debug mode.
When the ‘keyboard’ function is executed, Octave prints a prompt
and waits for user input. The input strings are then evaluated and
the results are printed. This makes it possible to examine the
values of variables within a function, and to assign new values if
necessary. To leave the prompt and return to normal execution type
‘return’ or ‘dbcont’. The ‘keyboard’ function does not return an
exit status.
If ‘keyboard’ is invoked without arguments, a default prompt of
‘debug> ’ is used.
See also: Note: dbstop, Note: dbcont, Note:
dbquit.
The ‘keyboard’ function is placed in a script at the point where the
user desires that the execution be stopped. It automatically sets the
running script into the debug mode.
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