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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.
Format the optional arguments under the control of the template string template using the same rules as the
printf
family of functions (see Formatted Output) and print the resulting message on thestderr
stream. The message is prefixed by the character string `error: '.Calling
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"); endcalling 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
Produce a beep from the speaker (or visual bell).
See also: puts, fputs, printf, fprintf.
Query or set the internal variable that controls whether Octave will try to ring the terminal bell before printing an error message.
Format the optional arguments under the control of the template string template using the same rules as the
printf
family of functions (see Formatted Output) and print the resulting message on thestderr
stream. The message is prefixed by the character string `warning: '. 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.The optional message identifier allows users to enable or disable warnings tagged by id. The special identifier `"all"' may be used to set the state of all warnings. — Built-in Function: warning ("on", id)
— Built-in Function: warning ("off", id)
— Built-in Function: warning ("error", id)
— Built-in Function: warning ("query", id)
Set or query the state of a particular warning using the identifier id. If the identifier is omitted, a value of `"all"' is assumed. If you set the state of a warning to `"error"', the warning named by id is handled as if it were an error instead.
See also: warning_ids.
Print the usage message for the currently executing function. The
print_usage
function is only intended to work inside a user-defined function.See also: help.
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
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)"); endifto check for the proper number of arguments.
Returns or sets the last error message. Called without any arguments returns a structure containing the last error message, as well as other information related to this error. The elements of this structure are:
- 'message'
- The text of the last error message
- 'identifier'
- The message identifier of this error message
- 'stack'
- A structure containing information on where the message occured. This might be an empty structure if this in the case where this information can not be obtained. The fields of this structure are:
- 'file'
- The name of the file where the error occurred
- 'name'
- The name of function in which the error occured
- 'line'
- The line number at which the error occured
- 'column'
- An optional field with the column number at which the error occurred
The err structure may also be passed to
lasterror
to set the information about the last error. The only constraint on err in that case is that it is a scalar structure. Any fields of err that match the above are set to the value passed in err, while other fields are set to their default values.If
lasterror
is called with the argument 'reset', all values take their default values.
Without any arguments, return the last error message. With one argument, set the last error message to msg. With two arguments, also set the last message identifier.
Without any arguments, return the last warning message. With one argument, set the last warning message to msg. With two arguments, also set the last message identifier.
Reissues a previous error as defined by err. err is a structure that must contain at least the 'message' and 'identifier' fields. err can also contain a field 'stack' that gives information on the assumed location of the error. Typically err is returned from
lasterror
.See also: lasterror, lasterr, error.
Octave:array-to-scalar
Octave:array-to-scalar
warning is enabled, Octave will
warn when an implicit conversion from an array to a scalar value is
attempted. By default, the Octave:array-to-scalar
warning is
disabled.
Octave:array-to-vector
Octave:array-to-vector
warning is enabled, Octave will
warn when an implicit conversion from an array to a vector value is
attempted. By default, the Octave:array-to-vector
warning is
disabled.
Octave:assign-as-truth-value
Octave:assign-as-truth-value
warning is
enabled, a warning is issued for statements like
if (s = t) ...
since such statements are not common, and it is likely that the intent was to write
if (s == t) ...
instead.
There are times when it is useful to write code that contains
assignments within the condition of a while
or if
statement. For example, statements like
while (c = getc()) ...
are common in C programming.
It is possible to avoid all warnings about such statements by
disabling the Octave:assign-as-truth-value
warning,
but that may also let real errors like
if (x = 1) # intended to test (x == 1)! ...
slip by.
In such cases, it is possible suppress errors for specific statements by writing them with an extra set of parentheses. For example, writing the previous example as
while ((c = getc())) ...
will prevent the warning from being printed for this statement, while allowing Octave to warn about other assignments used in conditional contexts.
By default, the Octave:assign-as-truth-value
warning is enabled.
Octave:associativity-change
Octave:associativity-change
warning is
enabled, Octave will warn about possible changes in the meaning of
some code due to changes in associativity for some operators.
Associativity changes have typically been made for Matlab
compatibility. By default, the Octave:associativity-change
warning is enabled.
Octave:divide-by-zero
Octave:divide-by-zero
warning is enabled, a
warning is issued when Octave encounters a division by zero. By
default, the Octave:divide-by-zero
warning is enabled.
Octave:empty-list-elements
Octave:empty-list-elements
warning is enabled, a
warning is issued when an empty matrix is found in a matrix list.
For example,
a = [1, [], 3, [], 5]
By default, the Octave:empty-list-elements
warning is enabled.
Octave:fortran-indexing
Octave:fortran-indexing
warning is enabled, a warning is
printed for expressions which select elements of a two-dimensional matrix
using a single index. By default, the Octave:fortran-indexing
warning is disabled.
Octave:function-name-clash
Octave:function-name-clash
warning is enabled, a
warning is issued when Octave finds that the name of a function
defined in a function file differs from the name of the file. (If
the names disagree, the name declared inside the file is ignored.)
By default, the Octave:function-name-clash
warning is enabled.
Octave:future-time-stamp
Octave:future-time-stamp
warning is enabled, Octave
will print a warning if it finds a function file with a time stamp
that is in the future. By default, the
Octave:future-time-stamp
warning is enabled.
Octave:imag-to-real
Octave:imag-to-real
warning is enabled, a warning is
printed for implicit conversions of complex numbers to real numbers.
By default, the Octave:imag-to-real
warning is disabled.
Octave:matlab-incompatible
Octave:missing-semicolon
Octave:missing-semicolon
warning is enabled, Octave
will warn when statements in function definitions don't end in
semicolons. By default the Octave:missing-semicolon
warning
is disabled.
Octave:neg-dim-as-zero
Octave:neg-dim-as-zero
warning is enabled, print a warning
for expressions like
eye (-1)
By default, the Octave:neg-dim-as-zero
warning is disabled.
Octave:num-to-str
Octave:num-to-str
warning is enable, a warning is
printed for implicit conversions of numbers to their ASCII character
equivalents when strings are constructed using a mixture of strings and
numbers in matrix notation. For example,
[ "f", 111, 111 ] => "foo"
elicits a warning if the Octave:num-to-str
warning is
enabled. By default, the Octave:num-to-str
warning is enabled.
Octave:precedence-change
Octave:precedence-change
warning is enabled, Octave
will warn about possible changes in the meaning of some code due to
changes in precedence for some operators. Precedence changes have
typically been made for Matlab compatibility. By default, the
Octave:precedence-change
warning is enabled.
Octave:reload-forces-clear
Octave:reload-forces-clear
warning is enabled, Octave will
warn you when this happens, and print a list of the additional
functions that it is forced to clear. By default, the
Octave:reload-forces-clear
warning is enabled.
Octave:resize-on-range-error
Octave:resize-on-range-error
warning is enabled, print a
warning when a matrix is resized by an indexed assignment with
indices outside the current bounds. By default, the
Octave:resize-on-range-error
warning is disabled.
Octave:separator-insert
Octave:single-quote-string
Octave:str-to-num
Octave:str-to-num
warning is enabled, a warning is printed
for implicit conversions of strings to their numeric ASCII equivalents.
For example,
"abc" + 0 => 97 98 99
elicits a warning if the Octave:str-to-num
warning is enabled.
By default, the Octave:str-to-num
warning is disabled.
Octave:string-concat
Octave:string-concat
warning is enabled, print a
warning when concatenating a mixture of double and single quoted strings.
By default, the Octave:string-concat
warning is disabled.
Octave:undefined-return-values
Octave:undefined-return-values
warning is disabled,
print a warning if a function does not define all the values in
the return list which are expected. By default, the
Octave:undefined-return-values
warning is enabled.
Octave:variable-switch-label
Octave:variable-switch-label
warning is enabled, Octave
will print a warning if a switch label is not a constant or constant
expression. By default, the Octave:variable-switch-label
warning is disabled.
Return the current value of the system-dependent variable errno, set its value to val and return the previous value, or return the named error code given name as a character string, or -1 if name is not found.
The following pair of functions are of limited usefulness, and may be removed from future versions of Octave.