octave: 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 ("query", ID)
-- : warning ("error", ID)
-- : warning (STATE, "backtrace")
-- : warning (STATE, ID, "local")
Display a warning message or control the behavior of Octave’s
warning system.
Format the optional arguments under the control of the template
string TEMPLATE using the same rules as the ‘printf’ family of
functions (
Formatted Output) and print the resulting
message on the ‘stderr’ 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. A message identifier is of the form
"NAMESPACE:WARNING-NAME". Octave’s own warnings use the "Octave"
namespace (warning_ids XREFwarning_ids.). The special
identifier "all" may be used to set the state of all warnings.
If the first argument is "on" or "off", set the state of a
particular warning using the identifier ID. If the first argument
is "query", query the state of this warning instead. 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. So, for example, the following
handles all warnings as errors:
warning ("error");
If the state is "on" or "off" and the third argument is
"backtrace", then a stack trace is printed along with the warning
message when warnings occur inside function calls. This option is
enabled by default.
If the state is "on", "off", or "error" and the third argument is
"local", 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.
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.
DONTPRINTYET See also: warning_ids XREFwarning_ids, *notelastwarn:
DONTPRINTYET See also: warning_ids XREFwarning_ids, lastwarn
XREFlastwarn, error XREFerror.
-- : [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.
DONTPRINTYET See also: warning XREFwarning, *notelasterror:
DONTPRINTYET See also: warning XREFwarning, lasterror
XREFlasterror, lasterr XREFlasterr.
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: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:fopen-file-in-path’
By default, the ‘Octave:fopen-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, Command Line Options.
‘Octave:load-file-in-path’
By default, the ‘Octave:load-file-in-path’ warning is enabled.
‘Octave:logical-conversion’
By default, the ‘Octave:logical-conversion’ 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: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 MATLAB always short circuits if
any logical operators are used in a condition. You can turn on the
option
do_braindead_shortcircuit_evaluation (1)
if you would like to enable this short-circuit evaluation in
Octave. Note that the ‘&&’ and ‘||’ operators always short circuit
in both Octave and MATLAB, so it’s only necessary to enable
MATLAB-style short-circuiting if it’s too arduous to modify
existing code that relies on this behavior. 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:nearly-singular-matrix’
‘Octave:singular-matrix’
By default, the ‘Octave:nearly-singular-matrix’ and
‘Octave:singular-matrix’ warnings are enabled.
‘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:undefined-return-values’
If the ‘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’
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.
Info Catalog
octave: Handling Warnings
octave: Enabling and Disabling Warnings