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<h4 class="subsection">12.2.2 Enabling and Disabling Warnings</h4>
<p>The <code>warning</code> function also allows you to control which warnings
are actually printed to the screen. If the <code>warning</code> function
is called with a string argument that is either <code>"on"</code> or <code>"off"</code>
all warnings will be enabled or disabled.
<p>It is also possible to enable and disable individual warnings through
their string identifications. The following code will issue a warning
<pre class="example"> warning ("non-negative-variable",
"'a' must be non-negative. Setting 'a' to zero.");
</pre>
<p class="noindent">while the following won't issue a warning
<pre class="example"> warning ("off", "non-negative-variable");
warning ("non-negative-variable",
"'a' must be non-negative. Setting 'a' to zero.");
</pre>
<p>The functions distributed with Octave can issue one of the following
warnings.
<!-- ./miscellaneous/warning_ids.m -->
<p><a name="doc_002dwarning_005fids"></a>
<dl>
<dt><code>Octave:array-to-scalar</code><dd>If the <code>Octave:array-to-scalar</code> warning is enabled, Octave will
warn when an implicit conversion from an array to a scalar value is
attempted. By default, the <code>Octave:array-to-scalar</code> warning is
disabled.
<br><dt><code>Octave:array-to-vector</code><dd>If the <code>Octave:array-to-vector</code> warning is enabled, Octave will
warn when an implicit conversion from an array to a vector value is
attempted. By default, the <code>Octave:array-to-vector</code> warning is
disabled.
<br><dt><code>Octave:assign-as-truth-value</code><dd>If the <code>Octave:assign-as-truth-value</code> warning is
enabled, a warning is issued for statements like
<pre class="example"> if (s = t)
...
</pre>
<p class="noindent">since such statements are not common, and it is likely that the intent
was to write
<pre class="example"> if (s == t)
...
</pre>
<p class="noindent">instead.
<p>There are times when it is useful to write code that contains
assignments within the condition of a <code>while</code> or <code>if</code>
statement. For example, statements like
<pre class="example"> while (c = getc())
...
</pre>
<p class="noindent">are common in C programming.
<p>It is possible to avoid all warnings about such statements by
disabling the <code>Octave:assign-as-truth-value</code> warning,
but that may also let real errors like
<pre class="example"> if (x = 1) # intended to test (x == 1)!
...
</pre>
<p class="noindent">slip by.
<p>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
<pre class="example"> while ((c = getc()))
...
</pre>
<p class="noindent">will prevent the warning from being printed for this statement, while
allowing Octave to warn about other assignments used in conditional
contexts.
<p>By default, the <code>Octave:assign-as-truth-value</code> warning is enabled.
<br><dt><code>Octave:associativity-change</code><dd>If the <code>Octave:associativity-change</code> 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 <span class="sc">matlab</span>
compatibility. By default, the <code>Octave:associativity-change</code>
warning is enabled.
<br><dt><code>Octave:divide-by-zero</code><dd>If the <code>Octave:divide-by-zero</code> warning is enabled, a
warning is issued when Octave encounters a division by zero. By
default, the <code>Octave:divide-by-zero</code> warning is enabled.
<br><dt><code>Octave:empty-list-elements</code><dd>If the <code>Octave:empty-list-elements</code> warning is enabled, a
warning is issued when an empty matrix is found in a matrix list.
For example,
<pre class="example"> a = [1, [], 3, [], 5]
</pre>
<p class="noindent">By default, the <code>Octave:empty-list-elements</code> warning is enabled.
<br><dt><code>Octave:fortran-indexing</code><dd>If the <code>Octave:fortran-indexing</code> warning is enabled, a warning is
printed for expressions which select elements of a two-dimensional matrix
using a single index. By default, the <code>Octave:fortran-indexing</code>
warning is disabled.
<br><dt><code>Octave:function-name-clash</code><dd>If the <code>Octave:function-name-clash</code> 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 <code>Octave:function-name-clash</code> warning is enabled.
<br><dt><code>Octave:future-time-stamp</code><dd>If the <code>Octave:future-time-stamp</code> 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
<code>Octave:future-time-stamp</code> warning is enabled.
<br><dt><code>Octave:imag-to-real</code><dd>If the <code>Octave:imag-to-real</code> warning is enabled, a warning is
printed for implicit conversions of complex numbers to real numbers.
By default, the <code>Octave:imag-to-real</code> warning is disabled.
<br><dt><code>Octave:matlab-incompatible</code><dd>Print warnings for Octave language features that may cause
compatibility problems with <span class="sc">matlab</span>.
<br><dt><code>Octave:missing-semicolon</code><dd>If the <code>Octave:missing-semicolon</code> warning is enabled, Octave
will warn when statements in function definitions don't end in
semicolons. By default the <code>Octave:missing-semicolon</code> warning
is disabled.
<br><dt><code>Octave:neg-dim-as-zero</code><dd>If the <code>Octave:neg-dim-as-zero</code> warning is enabled, print a warning
for expressions like
<pre class="example"> eye (-1)
</pre>
<p class="noindent">By default, the <code>Octave:neg-dim-as-zero</code> warning is disabled.
<br><dt><code>Octave:num-to-str</code><dd>If the <code>Octave:num-to-str</code> 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,
<pre class="example"> [ "f", 111, 111 ]
⇒ "foo"
</pre>
<p>elicits a warning if the <code>Octave:num-to-str</code> warning is
enabled. By default, the <code>Octave:num-to-str</code> warning is enabled.
<br><dt><code>Octave:precedence-change</code><dd>If the <code>Octave:precedence-change</code> 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 <span class="sc">matlab</span> compatibility. By default, the
<code>Octave:precedence-change</code> warning is enabled.
<br><dt><code>Octave:reload-forces-clear</code><dd>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 <code>Octave:reload-forces-clear</code> 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
<code>Octave:reload-forces-clear</code> warning is enabled.
<br><dt><code>Octave:resize-on-range-error</code><dd>If the <code>Octave:resize-on-range-error</code> warning is enabled, print a
warning when a matrix is resized by an indexed assignment with
indices outside the current bounds. By default, the
<code>Octave:resize-on-range-error</code> warning is disabled.
<br><dt><code>Octave:separator-insert</code><dd>Print warning if commas or semicolons might be inserted
automatically in literal matrices.
<br><dt><code>Octave:single-quote-string</code><dd>Print warning if a single quote character is used to introduce a
string constant.
<br><dt><code>Octave:str-to-num</code><dd>If the <code>Octave:str-to-num</code> warning is enabled, a warning is printed
for implicit conversions of strings to their numeric ASCII equivalents.
For example,
<pre class="example"> "abc" + 0
⇒ 97 98 99
</pre>
<p>elicits a warning if the <code>Octave:str-to-num</code> warning is enabled.
By default, the <code>Octave:str-to-num</code> warning is disabled.
<br><dt><code>Octave:string-concat</code><dd>If the <code>Octave:string-concat</code> warning is enabled, print a
warning when concatenating a mixture of double and single quoted strings.
By default, the <code>Octave:string-concat</code> warning is disabled.
<br><dt><code>Octave:undefined-return-values</code><dd>If the <code>Octave:undefined-return-values</code> 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
<code>Octave:undefined-return-values</code> warning is enabled.
<br><dt><code>Octave:variable-switch-label</code><dd>If the <code>Octave:variable-switch-label</code> warning is enabled, Octave
will print a warning if a switch label is not a constant or constant
expression. By default, the <code>Octave:variable-switch-label</code>
warning is disabled.
</dl>
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