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<title>Debugging with GDB: Type Checking</title>
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<a name="Type-Checking"></a>
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<div class="header">
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<p>
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Next: <a href="Range-Checking.html#Range-Checking" accesskey="n" rel="next">Range Checking</a>, Up: <a href="Checks.html#Checks" accesskey="u" rel="up">Checks</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<a name="An-Overview-of-Type-Checking"></a>
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<h4 class="subsection">15.3.1 An Overview of Type Checking</h4>
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<p>Some languages, such as C and C<tt>++</tt>, are strongly typed, meaning that the
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arguments to operators and functions have to be of the correct type,
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otherwise an error occurs. These checks prevent type mismatch
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errors from ever causing any run-time problems. For example,
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</p>
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<div class="smallexample">
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<pre class="smallexample">int klass::my_method(char *b) { return b ? 1 : 2; }
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(gdb) print obj.my_method (0)
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$1 = 2
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</pre><pre class="smallexample">but
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</pre><pre class="smallexample">(gdb) print obj.my_method (0x1234)
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Cannot resolve method klass::my_method to any overloaded instance
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</pre></div>
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<p>The second example fails because in C<tt>++</tt> the integer constant
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‘<samp>0x1234</samp>’ is not type-compatible with the pointer parameter type.
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</p>
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<p>For the expressions you use in <small>GDB</small> commands, you can tell
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<small>GDB</small> to not enforce strict type checking or
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to treat any mismatches as errors and abandon the expression;
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When type checking is disabled, <small>GDB</small> successfully evaluates
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expressions like the second example above.
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</p>
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<p>Even if type checking is off, there may be other reasons
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related to type that prevent <small>GDB</small> from evaluating an expression.
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For instance, <small>GDB</small> does not know how to add an <code>int</code> and
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a <code>struct foo</code>. These particular type errors have nothing to do
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with the language in use and usually arise from expressions which make
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little sense to evaluate anyway.
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</p>
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<p><small>GDB</small> provides some additional commands for controlling type checking:
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</p>
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<a name="index-set-check-type"></a>
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<a name="index-show-check-type"></a>
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<dl compact="compact">
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<dt><code>set check type on</code></dt>
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<dt><code>set check type off</code></dt>
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<dd><p>Set strict type checking on or off. If any type mismatches occur in
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evaluating an expression while type checking is on, <small>GDB</small> prints a
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message and aborts evaluation of the expression.
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</p>
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</dd>
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<dt><code>show check type</code></dt>
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<dd><p>Show the current setting of type checking and whether <small>GDB</small>
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is enforcing strict type checking rules.
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</p></dd>
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</dl>
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<a name="index-range-checking"></a>
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<a name="index-checks_002c-range"></a>
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Next: <a href="Range-Checking.html#Range-Checking" accesskey="n" rel="next">Range Checking</a>, Up: <a href="Checks.html#Checks" accesskey="u" rel="up">Checks</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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