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diff --git a/share/doc/gdb/Pretty-Printing-API.html b/share/doc/gdb/Pretty-Printing-API.html new file mode 100644 index 0000000..84aab1e --- /dev/null +++ b/share/doc/gdb/Pretty-Printing-API.html @@ -0,0 +1,209 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Free Software" and "Free Software Needs +Free Documentation", with the Front-Cover Texts being "A GNU Manual," +and with the Back-Cover Texts as in (a) below. + +(a) The FSF's Back-Cover Text is: "You are free to copy and modify +this GNU Manual. Buying copies from GNU Press supports the FSF in +developing GNU and promoting software freedom." --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Debugging with GDB: Pretty Printing API</title> + +<meta name="description" content="Debugging with GDB: Pretty Printing API"> +<meta name="keywords" content="Debugging with GDB: Pretty Printing API"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Concept-Index.html#Concept-Index" rel="index" title="Concept Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="Python-API.html#Python-API" rel="up" title="Python API"> +<link href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" rel="next" title="Selecting Pretty-Printers"> +<link href="Types-In-Python.html#Types-In-Python" rel="previous" title="Types In Python"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Pretty-Printing-API"></a> +<div class="header"> +<p> +Next: <a href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Pretty-Printers</a>, Previous: <a href="Types-In-Python.html#Types-In-Python" accesskey="p" rel="previous">Types In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</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> +</div> +<hr> +<a name="Pretty-Printing-API-1"></a> +<h4 class="subsubsection">23.3.2.5 Pretty Printing API</h4> +<a name="index-python-pretty-printing-api"></a> + +<p>A pretty-printer is just an object that holds a value and implements a +specific interface, defined here. An example output is provided +(see <a href="Pretty-Printing.html#Pretty-Printing">Pretty Printing</a>). +</p> +<dl> +<dt><a name="index-pretty_005fprinter_002echildren"></a>Function: <strong>pretty_printer.children</strong> <em>(self)</em></dt> +<dd><p><small>GDB</small> will call this method on a pretty-printer to compute the +children of the pretty-printer’s value. +</p> +<p>This method must return an object conforming to the Python iterator +protocol. Each item returned by the iterator must be a tuple holding +two elements. The first element is the “name” of the child; the +second element is the child’s value. The value can be any Python +object which is convertible to a <small>GDB</small> value. +</p> +<p>This method is optional. If it does not exist, <small>GDB</small> will act +as though the value has no children. +</p> +<p>For efficiency, the <code>children</code> method should lazily compute its +results. This will let <small>GDB</small> read as few elements as +necessary, for example when various print settings (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>) or <code>-var-list-children</code> (see <a href="GDB_002fMI-Variable-Objects.html#GDB_002fMI-Variable-Objects">GDB/MI Variable Objects</a>) limit the number of elements to be displayed. +</p> +<p>Children may be hidden from display based on the value of ‘<samp>set +print max-depth</samp>’ (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>). +</p></dd></dl> + +<dl> +<dt><a name="index-pretty_005fprinter_002edisplay_005fhint"></a>Function: <strong>pretty_printer.display_hint</strong> <em>(self)</em></dt> +<dd><p>The CLI may call this method and use its result to change the +formatting of a value. The result will also be supplied to an MI +consumer as a ‘<samp>displayhint</samp>’ attribute of the variable being +printed. +</p> +<p>This method is optional. If it does exist, this method must return a +string or the special value <code>None</code>. +</p> +<p>Some display hints are predefined by <small>GDB</small>: +</p> +<dl compact="compact"> +<dt>‘<samp>array</samp>’</dt> +<dd><p>Indicate that the object being printed is “array-like”. The CLI +uses this to respect parameters such as <code>set print elements</code> and +<code>set print array</code>. +</p> +</dd> +<dt>‘<samp>map</samp>’</dt> +<dd><p>Indicate that the object being printed is “map-like”, and that the +children of this value can be assumed to alternate between keys and +values. +</p> +</dd> +<dt>‘<samp>string</samp>’</dt> +<dd><p>Indicate that the object being printed is “string-like”. If the +printer’s <code>to_string</code> method returns a Python string of some +kind, then <small>GDB</small> will call its internal language-specific +string-printing function to format the string. For the CLI this means +adding quotation marks, possibly escaping some characters, respecting +<code>set print elements</code>, and the like. +</p></dd> +</dl> + +<p>The special value <code>None</code> causes <small>GDB</small> to apply the default +display rules. +</p></dd></dl> + +<dl> +<dt><a name="index-pretty_005fprinter_002eto_005fstring"></a>Function: <strong>pretty_printer.to_string</strong> <em>(self)</em></dt> +<dd><p><small>GDB</small> will call this method to display the string +representation of the value passed to the object’s constructor. +</p> +<p>When printing from the CLI, if the <code>to_string</code> method exists, +then <small>GDB</small> will prepend its result to the values returned by +<code>children</code>. Exactly how this formatting is done is dependent on +the display hint, and may change as more hints are added. Also, +depending on the print settings (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>), the CLI may +print just the result of <code>to_string</code> in a stack trace, omitting +the result of <code>children</code>. +</p> +<p>If this method returns a string, it is printed verbatim. +</p> +<p>Otherwise, if this method returns an instance of <code>gdb.Value</code>, +then <small>GDB</small> prints this value. This may result in a call to +another pretty-printer. +</p> +<p>If instead the method returns a Python value which is convertible to a +<code>gdb.Value</code>, then <small>GDB</small> performs the conversion and prints +the resulting value. Again, this may result in a call to another +pretty-printer. Python scalars (integers, floats, and booleans) and +strings are convertible to <code>gdb.Value</code>; other types are not. +</p> +<p>Finally, if this method returns <code>None</code> then no further operations +are peformed in this method and nothing is printed. +</p> +<p>If the result is not one of these types, an exception is raised. +</p></dd></dl> + +<p><small>GDB</small> provides a function which can be used to look up the +default pretty-printer for a <code>gdb.Value</code>: +</p> +<a name="index-gdb_002edefault_005fvisualizer"></a> +<dl> +<dt><a name="index-gdb_002edefault_005fvisualizer-1"></a>Function: <strong>gdb.default_visualizer</strong> <em>(value)</em></dt> +<dd><p>This function takes a <code>gdb.Value</code> object as an argument. If a +pretty-printer for this value exists, then it is returned. If no such +printer exists, then this returns <code>None</code>. +</p></dd></dl> + +<p>Normally, a pretty-printer can respect the user’s print settings +(including temporarily applied settings, such as ‘<samp>/x</samp>’) simply by +calling <code>Value.format_string</code> (see <a href="Values-From-Inferior.html#Values-From-Inferior">Values From Inferior</a>). +However, these settings can also be queried directly: +</p> +<a name="index-gdb_002eprint_005foptions"></a> +<dl> +<dt><a name="index-gdb_002eprint_005foptions-1"></a>Function: <strong>gdb.print_options</strong> <em>()</em></dt> +<dd><p>Return a dictionary whose keys are the valid keywords that can be +given to <code>Value.format_string</code>, and whose values are the user’s +settings. During a <code>print</code> or other operation, the values will +reflect any flags that are temporarily in effect. +</p> +<div class="smallexample"> +<pre class="smallexample">(gdb) python print (gdb.print_options ()['max_elements']) +200 +</pre></div> +</dd></dl> + +<hr> +<div class="header"> +<p> +Next: <a href="Selecting-Pretty_002dPrinters.html#Selecting-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Pretty-Printers</a>, Previous: <a href="Types-In-Python.html#Types-In-Python" accesskey="p" rel="previous">Types In Python</a>, Up: <a href="Python-API.html#Python-API" accesskey="u" rel="up">Python API</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> +</div> + + + +</body> +</html> |