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 <h3 class="section">10.2 Ambiguous Expressions</h3>

 <p><a name="index-ambiguous-expressions-632"></a>
 Expressions can sometimes contain some ambiguous elements.  For instance,
 some programming languages (notably Ada, C<tt>++</tt> and Objective-C) permit
 a single function name to be defined several times, for application in
 different contexts.  This is called <dfn>overloading</dfn>.  Another example
 involving Ada is generics.  A <dfn>generic package</dfn> is similar to C<tt>++</tt>
 templates and is typically instantiated several times, resulting in
 the same function name being defined in different contexts.

    <p>In some cases and depending on the language, it is possible to adjust
 the expression to remove the ambiguity.  For instance in C<tt>++</tt>, you
 can specify the signature of the function you want to break on, as in
 <kbd>break </kbd><var>function</var><kbd>(</kbd><var>types</var><kbd>)</kbd>.  In Ada, using the fully
 qualified name of your function often makes the expression unambiguous
 as well.

    <p>When an ambiguity that needs to be resolved is detected, the debugger
 has the capability to display a menu of numbered choices for each
 possibility, and then waits for the selection with the prompt &lsquo;<samp><span class="samp">&gt;</span></samp>&rsquo;.
 The first option is always &lsquo;<samp><span class="samp">[0] cancel</span></samp>&rsquo;, and typing <kbd>0 &lt;RET&gt;</kbd>
 aborts the current command.  If the command in which the expression was
 used allows more than one choice to be selected, the next option in the
 menu is &lsquo;<samp><span class="samp">[1] all</span></samp>&rsquo;, and typing <kbd>1 &lt;RET&gt;</kbd> selects all possible
 choices.

    <p>For example, the following session excerpt shows an attempt to set a
 breakpoint at the overloaded symbol <code>String::after</code>.
 We choose three particular definitions of that function name:

 <!-- FIXME! This is likely to change to show arg type lists, at least -->
 <pre class="smallexample">     (gdb) b String::after
      [0] cancel
      [1] all
      [2] file:String.cc; line number:867
      [3] file:String.cc; line number:860
      [4] file:String.cc; line number:875
      [5] file:String.cc; line number:853
      [6] file:String.cc; line number:846
      [7] file:String.cc; line number:735
      &gt; 2 4 6
      Breakpoint 1 at 0xb26c: file String.cc, line 867.
      Breakpoint 2 at 0xb344: file String.cc, line 875.
      Breakpoint 3 at 0xafcc: file String.cc, line 846.
      Multiple breakpoints were set.
      Use the "delete" command to delete unwanted
       breakpoints.
      (gdb)
 </pre>

 <a name="index-set-multiple_002dsymbols-633"></a>
 <dl><dt><code>set multiple-symbols </code><var>mode</var><dd><a name="index-multiple_002dsymbols-menu-634"></a>
 This option allows you to adjust the debugger behavior when an expression
 is ambiguous.

      <p>By default, <var>mode</var> is set to <code>all</code>.  If the command with which
 the expression is used allows more than one choice, then <span class="sc">gdb</span>
 automatically selects all possible choices.  For instance, inserting
 a breakpoint on a function using an ambiguous name results in a breakpoint
 inserted on each possible match.  However, if a unique choice must be made,
 then <span class="sc">gdb</span> uses the menu to help you disambiguate the expression.
 For instance, printing the address of an overloaded function will result
 in the use of the menu.

      <p>When <var>mode</var> is set to <code>ask</code>, the debugger always uses the menu
 when an ambiguity is detected.

      <p>Finally, when <var>mode</var> is set to <code>cancel</code>, the debugger reports
 an error due to the ambiguity and the command is aborted.

      <p><a name="index-show-multiple_002dsymbols-635"></a><br><dt><code>show multiple-symbols</code><dd>Show the current value of the <code>multiple-symbols</code> setting.
 </dl>

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	<hr>
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	<h3 class="section">10.2 Ambiguous Expressions</h3>

	<p><a name="index-ambiguous-expressions-632"></a>
	Expressions can sometimes contain some ambiguous elements. For instance,
	some programming languages (notably Ada, C<tt>++</tt> and Objective-C) permit
	a single function name to be defined several times, for application in
	different contexts. This is called <dfn>overloading</dfn>. Another example
	involving Ada is generics. A <dfn>generic package</dfn> is similar to C<tt>++</tt>
	templates and is typically instantiated several times, resulting in
	the same function name being defined in different contexts.

	<p>In some cases and depending on the language, it is possible to adjust
	the expression to remove the ambiguity. For instance in C<tt>++</tt>, you
	can specify the signature of the function you want to break on, as in
	<kbd>break </kbd><var>function</var><kbd>(</kbd><var>types</var><kbd>)</kbd>. In Ada, using the fully
	qualified name of your function often makes the expression unambiguous
	as well.

	<p>When an ambiguity that needs to be resolved is detected, the debugger
	has the capability to display a menu of numbered choices for each
	possibility, and then waits for the selection with the prompt ‘<samp><span class="samp">></span></samp>’.
	The first option is always ‘<samp><span class="samp">[0] cancel</span></samp>’, and typing <kbd>0 <RET></kbd>
	aborts the current command. If the command in which the expression was
	used allows more than one choice to be selected, the next option in the
	menu is ‘<samp><span class="samp">[1] all</span></samp>’, and typing <kbd>1 <RET></kbd> selects all possible
	choices.

	<p>For example, the following session excerpt shows an attempt to set a
	breakpoint at the overloaded symbol <code>String::after</code>.
	We choose three particular definitions of that function name:

	<!-- FIXME! This is likely to change to show arg type lists, at least -->
	<pre class="smallexample"> (gdb) b String::after
	[0] cancel
	[1] all
	[2] file:String.cc; line number:867
	[3] file:String.cc; line number:860
	[4] file:String.cc; line number:875
	[5] file:String.cc; line number:853
	[6] file:String.cc; line number:846
	[7] file:String.cc; line number:735
	> 2 4 6
	Breakpoint 1 at 0xb26c: file String.cc, line 867.
	Breakpoint 2 at 0xb344: file String.cc, line 875.
	Breakpoint 3 at 0xafcc: file String.cc, line 846.
	Multiple breakpoints were set.
	Use the "delete" command to delete unwanted
	breakpoints.
	(gdb)
	</pre>

	<a name="index-set-multiple_002dsymbols-633"></a>
	<dl><dt><code>set multiple-symbols </code><var>mode</var><dd><a name="index-multiple_002dsymbols-menu-634"></a>
	This option allows you to adjust the debugger behavior when an expression
	is ambiguous.

	<p>By default, <var>mode</var> is set to <code>all</code>. If the command with which
	the expression is used allows more than one choice, then <span class="sc">gdb</span>
	automatically selects all possible choices. For instance, inserting
	a breakpoint on a function using an ambiguous name results in a breakpoint
	inserted on each possible match. However, if a unique choice must be made,
	then <span class="sc">gdb</span> uses the menu to help you disambiguate the expression.
	For instance, printing the address of an overloaded function will result
	in the use of the menu.

	<p>When <var>mode</var> is set to <code>ask</code>, the debugger always uses the menu
	when an ambiguity is detected.

	<p>Finally, when <var>mode</var> is set to <code>cancel</code>, the debugger reports
	an error due to the ambiguity and the command is aborted.

	<p><a name="index-show-multiple_002dsymbols-635"></a><br><dt><code>show multiple-symbols</code><dd>Show the current value of the <code>multiple-symbols</code> setting.
	</dl>

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