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| <title>Debugging with GDB: Exception Handling</title> |
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| <a name="Exception-Handling"></a> |
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| <a name="Exception-Handling-1"></a> |
| <h4 class="subsubsection">23.2.2.2 Exception Handling</h4> |
| <a name="index-python-exceptions"></a> |
| <a name="index-exceptions_002c-python"></a> |
| |
| <p>When executing the <code>python</code> command, Python exceptions |
| uncaught within the Python code are translated to calls to |
| <small>GDB</small> error-reporting mechanism. If the command that called |
| <code>python</code> does not handle the error, <small>GDB</small> will |
| terminate it and print an error message containing the Python |
| exception name, the associated value, and the Python call stack |
| backtrace at the point where the exception was raised. Example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) python print foo |
| Traceback (most recent call last): |
| File "<string>", line 1, in <module> |
| NameError: name 'foo' is not defined |
| </pre></div> |
| |
| <p><small>GDB</small> errors that happen in <small>GDB</small> commands invoked by |
| Python code are converted to Python exceptions. The type of the |
| Python exception depends on the error. |
| </p> |
| <dl compact="compact"> |
| <dt><code>gdb.error</code> |
| <a name="index-gdb_002eerror"></a> |
| </dt> |
| <dd><p>This is the base class for most exceptions generated by <small>GDB</small>. |
| It is derived from <code>RuntimeError</code>, for compatibility with earlier |
| versions of <small>GDB</small>. |
| </p> |
| <p>If an error occurring in <small>GDB</small> does not fit into some more |
| specific category, then the generated exception will have this type. |
| </p> |
| </dd> |
| <dt><code>gdb.MemoryError</code> |
| <a name="index-gdb_002eMemoryError"></a> |
| </dt> |
| <dd><p>This is a subclass of <code>gdb.error</code> which is thrown when an |
| operation tried to access invalid memory in the inferior. |
| </p> |
| </dd> |
| <dt><code>KeyboardInterrupt</code> |
| <a name="index-KeyboardInterrupt"></a> |
| </dt> |
| <dd><p>User interrupt (via <kbd>C-c</kbd> or by typing <kbd>q</kbd> at a pagination |
| prompt) is translated to a Python <code>KeyboardInterrupt</code> exception. |
| </p></dd> |
| </dl> |
| |
| <p>In all cases, your exception handler will see the <small>GDB</small> error |
| message as its value and the Python call stack backtrace at the Python |
| statement closest to where the <small>GDB</small> error occured as the |
| traceback. |
| </p> |
| <a name="index-gdb_002eGdbError"></a> |
| <p>When implementing <small>GDB</small> commands in Python via <code>gdb.Command</code>, |
| it is useful to be able to throw an exception that doesn’t cause a |
| traceback to be printed. For example, the user may have invoked the |
| command incorrectly. Use the <code>gdb.GdbError</code> exception |
| to handle this case. Example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) python |
| >class HelloWorld (gdb.Command): |
| > """Greet the whole world.""" |
| > def __init__ (self): |
| > super (HelloWorld, self).__init__ ("hello-world", gdb.COMMAND_USER) |
| > def invoke (self, args, from_tty): |
| > argv = gdb.string_to_argv (args) |
| > if len (argv) != 0: |
| > raise gdb.GdbError ("hello-world takes no arguments") |
| > print "Hello, World!" |
| >HelloWorld () |
| >end |
| (gdb) hello-world 42 |
| hello-world takes no arguments |
| </pre></div> |
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