(octave.info)Issuing Warnings
12.2.1 Issuing Warnings
-----------------------
It is possible to issue warnings from any code using the ‘warning’
function. In its most simple form, the ‘warning’ function takes a
string describing the warning as its input argument. As an example, the
following code controls if the variable ‘a’ is non-negative, and if not
issues a warning and sets ‘a’ to zero.
a = -1;
if (a < 0)
warning ("'a' must be non-negative. Setting 'a' to zero.");
a = 0;
endif
⊣ 'a' must be non-negative. Setting 'a' to zero.
Since warnings aren’t fatal to a running program, it is not possible
to catch a warning using the ‘try’ statement or something similar. It
is however possible to access the last warning as a string using the
‘lastwarn’ function.
It is also possible to assign an identification string to a warning.
If a warning has such an ID the user can enable and disable this warning
as will be described in the next section. To assign an ID to a warning,
simply call ‘warning’ with two string arguments, where the first is the
identification string, and the second is the actual warning. Note that
warning IDs are in the format "NAMESPACE:WARNING-NAME". The namespace
"Octave" is used for Octave’s own warnings. Any other string is
available as a namespace for user’s own warnings.
-- : warning (TEMPLATE, ...)
-- : warning (ID, TEMPLATE, ...)
-- : warning ("on", ID)
-- : warning ("off", ID)
-- : warning ("error", ID)
-- : warning ("query", ID)
-- : warning (STATE, ID, "local")
-- : warning (WARNING_STRUCT)
-- : WARNING_STRUCT = warning (...)
-- : warning (STATE, MODE)
Display a warning message or control the behavior of Octave’s
warning system.
The first call form uses a template TEMPLATE and optional
additional arguments to display a message on the ‘stderr’ stream.
The message is formatted using the same rules as the ‘printf’
family of functions (Note: Formatted Output) and 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. For example:
warning ("foo: maybe something wrong here");
The optional warning identifier ID allows users to enable or
disable warnings tagged by this identifier. A message identifier
is a string of the form "NAMESPACE:WARNING-NAME". Octave’s own
warnings use the "Octave" namespace (*note warning_ids:
XREFwarning_ids.). For example:
warning ("MyNameSpace:check-something",
"foo: maybe something wrong here");
The second call form is meant to change and/or query the state of
warnings. The first input argument must be a string STATE ("on",
"off", "error", or "query") followed by an optional warning
identifier ID or "all" (default).
The optional output argument WARNING_STRUCT is a structure or
structure array with fields "state" and "identifier". The STATE
argument may have the following values:
"on"|"off":
Enable or disable the display of warnings identified by ID and
optionally return their previous state STOUT.
"error":
Turn warnings identified by ID into errors and optionally
return their previous state STOUT.
"query":
Return the current state of warnings identified by ID.
A structure or structure array WARNING_STRUCT, with fields "state"
and "identifier", may be given as an input to achieve equivalent
results. The following example shows how to temporarily disable a
warning and then restore its original state:
loglog (-1:10);
## Disable the previous warning and save its original state
[~, id] = lastwarn ();
warnstate = warning ("off", id);
loglog (-1:10);
## Restore its original state
warning (warnstate);
If a final argument "local" is provided then the warning state will
be set temporarily until the end of the current function. Changes
to warning states that are set locally affect the current function
and all functions called from the current scope. The previous
warning state is restored on return from the current function. The
"local" option is ignored if used in the top-level workspace.
With no input argument ‘warning ()’ is equivalent to ‘warning
("query", "all")’ except that in the absence of an output argument,
the state of warnings is displayed on ‘stderr’.
The level of verbosity of the warning system may also be controlled
by two modes MODE:
"backtrace":
enable/disable the display of the stack trace after the
warning message
"verbose":
enable/disable the display of additional information after the
warning message
In this case the STATE argument may only be "on" or "off".
Implementation Note: For compatibility with MATLAB, escape
sequences in TEMPLATE (e.g., "\n" => newline) are processed
regardless of whether TEMPLATE has been defined with single quotes,
as long as there are two or more input arguments. To disable
escape sequence expansion use a second backslash before the
sequence (e.g., "\\n") or use the ‘regexptranslate’ function.
See also: Note: warning_ids, *note lastwarn:
XREFlastwarn, Note: error.
-- : [MSG, MSGID] = lastwarn ()
-- : lastwarn (MSG)
-- : lastwarn (MSG, MSGID)
Query or set the last warning message.
When called without input arguments, return the last warning
message and message identifier.
With one argument, set the last warning message to MSG.
With two arguments, also set the last message identifier.
See also: Note: warning, *note lasterror:
XREFlasterror, Note: lasterr.
The functions distributed with Octave can issue one of the following
warnings.
‘Octave:abbreviated-property-match’
By default, the ‘Octave:abbreviated-property-match’ warning is
enabled.
‘Octave:addpath-pkg’
If the ‘Octave:addpath-pkg’ warning is enabled, Octave will warn
when a package directory (i.e., +package_name) is added to the
‘path’. Typically, only the parent directory which contains the
package directory should be added to the load path. By default,
the ‘Octave:addpath-pkg’ warning is enabled.
‘Octave:array-as-logical’
If the ‘Octave:array-as-logical’ warning is enabled, Octave will
warn when an array of size greater than 1x1 is used as a truth
value in an if, while or until statement. By default, the
‘Octave:array-as-logical’ warning is disabled.
‘Octave:array-to-scalar’
If the ‘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’
If the ‘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’
If the ‘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’
If the ‘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:autoload-relative-file-name’
If the ‘Octave:autoload-relative-file-name’ is enabled, Octave will
warn when parsing autoload() function calls with relative paths to
function files. This usually happens when using autoload() calls
in PKG_ADD files, when the PKG_ADD file is not in the same
directory as the .oct file referred to by the autoload() command.
By default, the ‘Octave:autoload-relative-file-name’ warning is
enabled.
‘Octave:built-in-variable-assignment’
By default, the ‘Octave:built-in-variable-assignment’ warning is
enabled.
‘Octave:deprecated-function’
If the ‘Octave:deprecated-function’ warning is enabled, a warning
is issued when Octave encounters a function that is obsolete and
scheduled for removal from Octave. By default, the
‘Octave:deprecated-function’ warning is enabled.
‘Octave:deprecated-keyword’
If the ‘Octave:deprecated-keyword’ warning is enabled, a warning is
issued when Octave encounters a keyword that is obsolete and
scheduled for removal from Octave. By default, the
‘Octave:deprecated-keyword’ warning is enabled.
‘Octave:deprecated-property’
If the ‘Octave:deprecated-property’ warning is enabled, a warning
is issued when Octave encounters a graphics property that is
obsolete and scheduled for removal from Octave. By default, the
‘Octave:deprecated-property’ warning is enabled.
‘Octave:divide-by-zero’
If the ‘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:eigs:UnconvergedEigenvalues’
If the ‘Octave:eigs:UnconvergedEigenvalues’ warning is enabled then
the eigs function will issue a warning if the number of calculated
eigenvalues is less than the number of requested eigenvalues. By
default, the ‘Octave:eigs:UnconvergedEigenvalues’ warning is
enabled.
‘Octave:erase:chararray’
If the ‘Octave:erase:chararray’ warning is enabled then the erase
function will issue a warning if the input pattern is a character
array rather than a string or cell array of strings. By default,
the ‘Octave:erase:chararray’ warning is enabled.
‘Octave:data-file-in-path’
If the ‘Octave:data-file-in-path’ warning is enabled, a warning is
issued when Octave does not find the target of a file operation
such as ‘load’ or ‘fopen’ directly, but is able to locate the file
in Octave’s search ‘path’ for files. The warning could indicate
that a different file target than the programmer intended is being
used. By default, the ‘Octave:data-file-in-path’ warning is
enabled.
‘Octave:function-name-clash’
If the ‘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’
If the ‘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:glyph-render’
By default, the ‘Octave:glyph-render’ warning is enabled.
‘Octave:imag-to-real’
If the ‘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:language-extension’
Print warnings when using features that are unique to the Octave
language and that may still be missing in MATLAB. By default, the
‘Octave:language-extension’ warning is disabled. The
‘--traditional’ or ‘--braindead’ startup options for Octave may
also be of use, Note: Command Line Options.
‘Octave:logical-conversion’
By default, the ‘Octave:logical-conversion’ warning is enabled.
‘Octave:lu:sparse_input’
If the ‘Octave:lu:sparse_input’ warning is enabled, Octave will
warn when the lu function is called with a sparse input and less
than four output arguments. In this case, sparsity-preserving
column permutations are not performed and the result may be
inaccurate. By default, the ‘Octave:lu:sparse_input’ warning is
enabled.
‘Octave:missing-glyph’
By default, the ‘Octave:missing-glyph’ warning is enabled.
‘Octave:missing-semicolon’
If the ‘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:mixed-string-concat’
If the ‘Octave:mixed-string-concat’ warning is enabled, print a
warning when concatenating a mixture of double and single quoted
strings. By default, the ‘Octave:mixed-string-concat’ warning is
disabled.
‘Octave:nearly-singular-matrix’
‘Octave:singular-matrix’
By default, the ‘Octave:nearly-singular-matrix’ and
‘Octave:singular-matrix’ warnings are enabled.
‘Octave:neg-dim-as-zero’
If the ‘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:nested-functions-coerced’
By default, the ‘Octave:nested-functions-coerced’ warning is
enabled.
‘Octave:noninteger-range-as-index’
By default, the ‘Octave:noninteger-range-as-index’ warning is
enabled.
‘Octave:num-to-str’
If the ‘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:possible-matlab-short-circuit-operator’
If the ‘Octave:possible-matlab-short-circuit-operator’ warning is
enabled, Octave will warn about using the not short circuiting
operators ‘&’ and ‘|’ inside ‘if’ or ‘while’ conditions. They
normally never short circuit, but they do short circuit when used
in a condition. By default, the
‘Octave:possible-matlab-short-circuit-operator’ warning is enabled.
‘Octave:precedence-change’
If the ‘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:recursive-path-search’
By default, the ‘Octave:recursive-path-search’ warning is enabled.
‘Octave:remove-init-dir’
The ‘path’ function changes the search path that Octave uses to
find functions. It is possible to set the path to a value which
excludes Octave’s own built-in functions. If the
‘Octave:remove-init-dir’ warning is enabled then Octave will warn
when the ‘path’ function has been used in a way that may render
Octave unworkable. By default, the ‘Octave:remove-init-dir’
warning is enabled.
‘Octave:reload-forces-clear’
If several functions have been loaded from the same file, Octave
must clear all the functions before any one of them can be
reloaded. If the ‘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’
If the ‘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’
Print warning if commas or semicolons might be inserted
automatically in literal matrices. By default, the
‘Octave:separator-insert’ warning is disabled.
‘Octave:shadowed-function’
By default, the ‘Octave:shadowed-function’ warning is enabled.
‘Octave:single-quote-string’
Print warning if a single quote character is used to introduce a
string constant. By default, the ‘Octave:single-quote-string’
warning is disabled.
‘Octave:sqrtm:SingularMatrix’
By default, the ‘Octave:sqrtm:SingularMatrix’ warning is enabled.
‘Octave:str-to-num’
If the ‘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:variable-switch-label’
If the ‘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.
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