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| <a name="Command-Completion"></a> |
| <h3 class="section">3.2 Command Completion</h3> |
| |
| <a name="index-completion"></a> |
| <a name="index-word-completion"></a> |
| <p><small>GDB</small> can fill in the rest of a word in a command for you, if there is |
| only one possibility; it can also show you what the valid possibilities |
| are for the next word in a command, at any time. This works for <small>GDB</small> |
| commands, <small>GDB</small> subcommands, and the names of symbols in your program. |
| </p> |
| <p>Press the <tt class="key">TAB</tt> key whenever you want <small>GDB</small> to fill out the rest |
| of a word. If there is only one possibility, <small>GDB</small> fills in the |
| word, and waits for you to finish the command (or press <tt class="key">RET</tt> to |
| enter it). For example, if you type |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) info bre <span class="key">TAB</span> |
| </pre></div> |
| |
| <p><small>GDB</small> fills in the rest of the word ‘<samp>breakpoints</samp>’, since that is |
| the only <code>info</code> subcommand beginning with ‘<samp>bre</samp>’: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) info breakpoints |
| </pre></div> |
| |
| <p>You can either press <tt class="key">RET</tt> at this point, to run the <code>info |
| breakpoints</code> command, or backspace and enter something else, if |
| ‘<samp>breakpoints</samp>’ does not look like the command you expected. (If you |
| were sure you wanted <code>info breakpoints</code> in the first place, you |
| might as well just type <tt class="key">RET</tt> immediately after ‘<samp>info bre</samp>’, |
| to exploit command abbreviations rather than command completion). |
| </p> |
| <p>If there is more than one possibility for the next word when you press |
| <tt class="key">TAB</tt>, <small>GDB</small> sounds a bell. You can either supply more |
| characters and try again, or just press <tt class="key">TAB</tt> a second time; |
| <small>GDB</small> displays all the possible completions for that word. For |
| example, you might want to set a breakpoint on a subroutine whose name |
| begins with ‘<samp>make_</samp>’, but when you type <kbd>b make_<span class="key">TAB</span></kbd> <small>GDB</small> |
| just sounds the bell. Typing <tt class="key">TAB</tt> again displays all the |
| function names in your program that begin with those characters, for |
| example: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) b make_ <span class="key">TAB</span> |
| </pre><pre class="smallexample">GDB sounds bell; press <span class="key">TAB</span> again, to see: |
| </pre><pre class="smallexample">make_a_section_from_file make_environ |
| make_abs_section make_function_type |
| make_blockvector make_pointer_type |
| make_cleanup make_reference_type |
| make_command make_symbol_completion_list |
| (gdb) b make_ |
| </pre></div> |
| |
| <p>After displaying the available possibilities, <small>GDB</small> copies your |
| partial input (‘<samp>b make_</samp>’ in the example) so you can finish the |
| command. |
| </p> |
| <p>If you just want to see the list of alternatives in the first place, you |
| can press <kbd>M-?</kbd> rather than pressing <tt class="key">TAB</tt> twice. <kbd>M-?</kbd> |
| means <kbd><span class="key">META</span> ?</kbd>. You can type this either by holding down a |
| key designated as the <tt class="key">META</tt> shift on your keyboard (if there is |
| one) while typing <kbd>?</kbd>, or as <tt class="key">ESC</tt> followed by <kbd>?</kbd>. |
| </p> |
| <p>If the number of possible completions is large, <small>GDB</small> will |
| print as much of the list as it has collected, as well as a message |
| indicating that the list may be truncated. |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) b m<span class="key">TAB</span><span class="key">TAB</span> |
| main |
| <... the rest of the possible completions ...> |
| *** List may be truncated, max-completions reached. *** |
| (gdb) b m |
| </pre></div> |
| |
| <p>This behavior can be controlled with the following commands: |
| </p> |
| <dl compact="compact"> |
| <dd><a name="index-set-max_002dcompletions"></a> |
| </dd> |
| <dt><code>set max-completions <var>limit</var></code></dt> |
| <dt><code>set max-completions unlimited</code></dt> |
| <dd><p>Set the maximum number of completion candidates. <small>GDB</small> will |
| stop looking for more completions once it collects this many candidates. |
| This is useful when completing on things like function names as collecting |
| all the possible candidates can be time consuming. |
| The default value is 200. A value of zero disables tab-completion. |
| Note that setting either no limit or a very large limit can make |
| completion slow. |
| <a name="index-show-max_002dcompletions"></a> |
| </p></dd> |
| <dt><code>show max-completions</code></dt> |
| <dd><p>Show the maximum number of candidates that <small>GDB</small> will collect and show |
| during completion. |
| </p></dd> |
| </dl> |
| |
| <a name="index-quotes-in-commands"></a> |
| <a name="index-completion-of-quoted-strings"></a> |
| <p>Sometimes the string you need, while logically a “word”, may contain |
| parentheses or other characters that <small>GDB</small> normally excludes from |
| its notion of a word. To permit word completion to work in this |
| situation, you may enclose words in <code>'</code> (single quote marks) in |
| <small>GDB</small> commands. |
| </p> |
| <p>The most likely situation where you might need this is in typing the |
| name of a C<tt>++</tt> function. This is because C<tt>++</tt> allows function |
| overloading (multiple definitions of the same function, distinguished |
| by argument type). For example, when you want to set a breakpoint you |
| may need to distinguish whether you mean the version of <code>name</code> |
| that takes an <code>int</code> parameter, <code>name(int)</code>, or the version |
| that takes a <code>float</code> parameter, <code>name(float)</code>. To use the |
| word-completion facilities in this situation, type a single quote |
| <code>'</code> at the beginning of the function name. This alerts |
| <small>GDB</small> that it may need to consider more information than usual |
| when you press <tt class="key">TAB</tt> or <kbd>M-?</kbd> to request word completion: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) b 'bubble( <kbd>M-?</kbd> |
| bubble(double,double) bubble(int,int) |
| (gdb) b 'bubble( |
| </pre></div> |
| |
| <p>In some cases, <small>GDB</small> can tell that completing a name requires using |
| quotes. When this happens, <small>GDB</small> inserts the quote for you (while |
| completing as much as it can) if you do not type the quote in the first |
| place: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) b bub <span class="key">TAB</span> |
| </pre><pre class="smallexample">GDB alters your input line to the following, and rings a bell: |
| </pre><pre class="smallexample">(gdb) b 'bubble( |
| </pre></div> |
| |
| <p>In general, <small>GDB</small> can tell that a quote is needed (and inserts it) if |
| you have not yet started typing the argument list when you ask for |
| completion on an overloaded symbol. |
| </p> |
| <p>For more information about overloaded functions, see <a href="C-Plus-Plus-Expressions.html#C-Plus-Plus-Expressions">C<tt>++</tt> Expressions</a>. You can use the command <code>set |
| overload-resolution off</code> to disable overload resolution; |
| see <a href="Debugging-C-Plus-Plus.html#Debugging-C-Plus-Plus"><small>GDB</small> Features for C<tt>++</tt></a>. |
| </p> |
| <a name="index-completion-of-structure-field-names"></a> |
| <a name="index-structure-field-name-completion"></a> |
| <a name="index-completion-of-union-field-names"></a> |
| <a name="index-union-field-name-completion"></a> |
| <p>When completing in an expression which looks up a field in a |
| structure, <small>GDB</small> also tries<a name="DOCF2" href="#FOOT2"><sup>2</sup></a> to |
| limit completions to the field names available in the type of the |
| left-hand-side: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">(gdb) p gdb_stdout.<kbd>M-?</kbd> |
| magic to_fputs to_rewind |
| to_data to_isatty to_write |
| to_delete to_put to_write_async_safe |
| to_flush to_read |
| </pre></div> |
| |
| <p>This is because the <code>gdb_stdout</code> is a variable of the type |
| <code>struct ui_file</code> that is defined in <small>GDB</small> sources as |
| follows: |
| </p> |
| <div class="smallexample"> |
| <pre class="smallexample">struct ui_file |
| { |
| int *magic; |
| ui_file_flush_ftype *to_flush; |
| ui_file_write_ftype *to_write; |
| ui_file_write_async_safe_ftype *to_write_async_safe; |
| ui_file_fputs_ftype *to_fputs; |
| ui_file_read_ftype *to_read; |
| ui_file_delete_ftype *to_delete; |
| ui_file_isatty_ftype *to_isatty; |
| ui_file_rewind_ftype *to_rewind; |
| ui_file_put_ftype *to_put; |
| void *to_data; |
| } |
| </pre></div> |
| |
| |
| <div class="footnote"> |
| <hr> |
| <h4 class="footnotes-heading">Footnotes</h4> |
| |
| <h3><a name="FOOT2" href="#DOCF2">(2)</a></h3> |
| <p>The completer can be |
| confused by certain kinds of invalid expressions. Also, it only |
| examines the static type of the expression, not the dynamic type.</p> |
| </div> |
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