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4.8 KiB
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100 lines
4.8 KiB
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<title>Selecting Pretty-Printers - Debugging with GDB</title>
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Python-API.html#Python-API" title="Python API">
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<link rel="prev" href="Pretty-Printing-API.html#Pretty-Printing-API" title="Pretty Printing API">
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<link rel="next" href="Writing-a-Pretty_002dPrinter.html#Writing-a-Pretty_002dPrinter" title="Writing a Pretty-Printer">
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<div class="node">
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<a name="Selecting-Pretty-Printers"></a>
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<a name="Selecting-Pretty_002dPrinters"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Writing-a-Pretty_002dPrinter.html#Writing-a-Pretty_002dPrinter">Writing a Pretty-Printer</a>,
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Previous: <a rel="previous" accesskey="p" href="Pretty-Printing-API.html#Pretty-Printing-API">Pretty Printing API</a>,
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Up: <a rel="up" accesskey="u" href="Python-API.html#Python-API">Python API</a>
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<hr>
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</div>
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<h5 class="subsubsection">23.2.2.6 Selecting Pretty-Printers</h5>
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<p><a name="index-selecting-python-pretty_002dprinters-2010"></a>
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The Python list <code>gdb.pretty_printers</code> contains an array of
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functions or callable objects that have been registered via addition
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as a pretty-printer. Printers in this list are called <code>global</code>
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printers, they're available when debugging all inferiors.
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Each <code>gdb.Progspace</code> contains a <code>pretty_printers</code> attribute.
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Each <code>gdb.Objfile</code> also contains a <code>pretty_printers</code>
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attribute.
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<p>Each function on these lists is passed a single <code>gdb.Value</code>
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argument and should return a pretty-printer object conforming to the
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interface definition above (see <a href="Pretty-Printing-API.html#Pretty-Printing-API">Pretty Printing API</a>). If a function
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cannot create a pretty-printer for the value, it should return
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<code>None</code>.
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<p><span class="sc">gdb</span> first checks the <code>pretty_printers</code> attribute of each
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<code>gdb.Objfile</code> in the current program space and iteratively calls
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each enabled lookup routine in the list for that <code>gdb.Objfile</code>
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until it receives a pretty-printer object.
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If no pretty-printer is found in the objfile lists, <span class="sc">gdb</span> then
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searches the pretty-printer list of the current program space,
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calling each enabled function until an object is returned.
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After these lists have been exhausted, it tries the global
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<code>gdb.pretty_printers</code> list, again calling each enabled function until an
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object is returned.
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<p>The order in which the objfiles are searched is not specified. For a
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given list, functions are always invoked from the head of the list,
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and iterated over sequentially until the end of the list, or a printer
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object is returned.
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<p>For various reasons a pretty-printer may not work.
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For example, the underlying data structure may have changed and
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the pretty-printer is out of date.
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<p>The consequences of a broken pretty-printer are severe enough that
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<span class="sc">gdb</span> provides support for enabling and disabling individual
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printers. For example, if <code>print frame-arguments</code> is on,
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a backtrace can become highly illegible if any argument is printed
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with a broken printer.
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<p>Pretty-printers are enabled and disabled by attaching an <code>enabled</code>
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attribute to the registered function or callable object. If this attribute
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is present and its value is <code>False</code>, the printer is disabled, otherwise
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the printer is enabled.
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</body></html>
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