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