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| <h4 class="subsection">15.3.1 An Overview of Type Checking</h4> |
| |
| <p>Some languages, such as Modula-2, 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, |
| |
| <pre class="smallexample"> 1 + 2 ⇒ 3 |
| <br>but<br> |
| error--> 1 + 2.3 |
| </pre> |
| <p>The second example fails because the <code>CARDINAL</code> 1 is not |
| type-compatible with the <code>REAL</code> 2.3. |
| |
| <p>For the expressions you use in <span class="sc">gdb</span> commands, you can tell the |
| <span class="sc">gdb</span> type checker to skip checking; |
| to treat any mismatches as errors and abandon the expression; |
| or to only issue warnings when type mismatches occur, |
| but evaluate the expression anyway. When you choose the last of |
| these, <span class="sc">gdb</span> evaluates expressions like the second example above, but |
| also issues a warning. |
| |
| <p>Even if you turn type checking off, there may be other reasons |
| related to type that prevent <span class="sc">gdb</span> from evaluating an expression. |
| For instance, <span class="sc">gdb</span> 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, such as |
| the one described above, which make little sense to evaluate anyway. |
| |
| <p>Each language defines to what degree it is strict about type. For |
| instance, both Modula-2 and C require the arguments to arithmetical |
| operators to be numbers. In C, enumerated types and pointers can be |
| represented as numbers, so that they are valid arguments to mathematical |
| operators. See <a href="Supported-Languages.html#Supported-Languages">Supported Languages</a>, for further |
| details on specific languages. |
| |
| <p><span class="sc">gdb</span> provides some additional commands for controlling the type checker: |
| |
| <p><a name="index-set-check-type-787"></a><a name="index-show-check-type-788"></a> |
| <dl> |
| <dt><code>set check type auto</code><dd>Set type checking on or off based on the current working language. |
| See <a href="Supported-Languages.html#Supported-Languages">Supported Languages</a>, for the default settings for |
| each language. |
| |
| <br><dt><code>set check type on</code><dt><code>set check type off</code><dd>Set type checking on or off, overriding the default setting for the |
| current working language. Issue a warning if the setting does not |
| match the language default. If any type mismatches occur in |
| evaluating an expression while type checking is on, <span class="sc">gdb</span> prints a |
| message and aborts evaluation of the expression. |
| |
| <br><dt><code>set check type warn</code><dd>Cause the type checker to issue warnings, but to always attempt to |
| evaluate the expression. Evaluating the expression may still |
| be impossible for other reasons. For example, <span class="sc">gdb</span> cannot add |
| numbers and structures. |
| |
| <br><dt><code>show type</code><dd>Show the current setting of the type checker, and whether or not <span class="sc">gdb</span> |
| is setting it automatically. |
| </dl> |
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