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.
| error (template ...) | Built-in Function |
The error function formats the optional arguments under the
control of the template string template using the same rules as
the printf family of functions (see Formatted Output).
The resulting message is prefixed by the string error: and
printed on the stderr stream.
Calling 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 ()
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
|
| beep_on_error | Built-in Variable |
If the value of beep_on_error is nonzero Octave will try
to ring your terminal's bell before printing an error message. The
default value is 0.
|
| warning (msg) | Built-in Function |
Print a warning message msg prefixed by the string warning: .
After printing the warning message Octave will continue to execute
commands. You should use this function when you want to notify the user
of an unusual condition but only when it makes sense for your program
to go on.
|
| usage (msg) | Built-in Function |
Print the message msg prefixed by the string usage: , and
set 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.
After 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. |
| lasterr () | Built-in Function |
| lasterr (msg) | Built-in Function |
| Without any arguments return the last error message. With one argument set the last error message to msg. |
| lastwarn () | Built-in Function |
| lastwarn (msg) | Built-in Function |
| Without any arguments return the last warning message. With one argument set the last warning message to msg. |
The following pair of functions are of limited usefulness and may be removed from future versions of Octave.
| perror (name num) | Function File |
| Print the error message for function name corresponding to the error number num. This function is intended to be used to print useful error messages for those functions that return numeric error codes. |
| strerror (name num) | Function File |
| Return the text of an error message for function name corresponding to the error number num. This function is intended to be used to print useful error messages for those functions that return numeric error codes. |