Octave includes several functions for printing error and warning messages. When you write functions that need to take special action when they encounter abnormal conditions, you should print the error messages using the functions described in this chapter.
errorfunction formats the optional arguments under the control of the template string template using the same rules as the
printffamily of functions (see section Formatted Output). The resulting message is prefixed by the string `error: ' and printed on the
error also sets Octave's internal error state such that
control will return to the top level without evaluating any more
commands. This is useful for aborting from functions or scripts.
If the error message does not end with a new line character, Octave will print a traceback of all the function calls leading to the error. For example, given the following function definitions:
function f () g () end function g () h () end function h () nargin == 1 || error ("nargin != 1"); end
calling the function
f will result in a list of messages that
can help you to quickly locate the exact location of the error:
f () error: nargin != 1 error: evaluating index expression near line 1, column 30 error: evaluating binary operator `||' near line 1, column 27 error: called from `h' error: called from `g' error: called from `f'
If the error message ends in a new line character, Octave will print the message but will not display any traceback messages as it returns control to the top level. For example, modifying the error message in the previous example to end in a new line causes Octave to only print a single message:
function h () nargin == 1 || error ("nargin != 1\n"); end f () error: nargin != 1
trystatement or the try part of the most recent call to the
evalfunction. Outside of the
trystatements or the
evalfunction, or if no error has occurred within them, the value of
error_textis guaranteed to be the empty string.
Note that the message does not include the first `error: ' prefix,
so that it may easily be passed to the
error function without
See section The
try Statement and section The
beep_on_erroris nonzero, Octave will try to ring your terminal's bell before printing an error message. The default value is 0.
usage is evaluated, Octave will print a traceback of all
the function calls leading to the usage message.
You should use this function for reporting problems errors that result from an improper call to a function, such as calling a function with an incorrect number of arguments, or with arguments of the wrong type. For example, most functions distributed with Octave begin with code like this
if (nargin != 2) usage ("foo (a, b)"); endif
to check for the proper number of arguments.
The following pair of functions are of limited usefulness, and may be removed from future versions of Octave.
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