13.3 Breakpoints

Breakpoints can be set in any Octave function, using the dbstop function.

Loadable Function: rline = dbstop (func, line, …)

Set a breakpoint in a function

func

String representing the function name. When already in debug mode this should be left out and only the line should be given.

line

Line number you would like the breakpoint to be set on. Multiple lines might be given as separate arguments or as a vector.

The rline returned is the real line that the breakpoint was set at.

See also: dbclear, dbstatus, dbstep.

Note that breakpoints cannot be set in built-in functions (e.g., sin, etc.) or dynamically loaded function (i.e., oct-files). To set a breakpoint immediately on entering a function, the breakpoint should be set to line 1. The leading comment block will be ignored and the breakpoint will be set to the first executable statement in the function. For example

dbstop ("asind", 1)
⇒ 27

Note that the return value of 27 means that the breakpoint was effectively set to line 27. The status of breakpoints in a function can be queried with the dbstatus function.

Loadable Function: lst = dbstatus (func)

Return a vector containing the lines on which a function has breakpoints set.

func

String representing the function name. When already in debug mode this should be left out.

See also: dbclear, dbwhere.

Taking the above as an example, dbstatus ("asind") should return 27. The breakpoints can then be cleared with the dbclear function

Loadable Function: dbclear (func, line, …)

Delete a breakpoint in a function

func

String representing the function name. When already in debug mode this should be left out and only the line should be given.

line

Line number where you would like to remove the breakpoint. Multiple lines might be given as separate arguments or as a vector.

No checking is done to make sure that the line you requested is really a breakpoint. If you get the wrong line nothing will happen.

See also: dbstop, dbstatus, dbwhere.

These functions can be used to clear all the breakpoints in a function. For example,

dbclear ("asind", dbstatus ("asind"));

A breakpoint can 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", filemarker(), "func2"])
⇒ 5

Note that filemarker returns a character that marks the subfunctions from the file containing them.

Another simple way of setting a breakpoint in an Octave script is the use of the keyboard function.

Built-in Function: keyboard ()

Built-in Function: keyboard (prompt)

This function is normally used for simple debugging. 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: dbcont, dbquit.

The keyboard function is typically placed in a script at the point where the user desires that the execution is stopped. It automatically sets the running script into the debug mode.