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

<p><a name="index-ambiguous-expressions-501"></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-502"></a>
<dl><dt><code>set multiple-symbols </code><var>mode</var><dd><a name="index-multiple_002dsymbols-menu-503"></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-504"></a><br><dt><code>show multiple-symbols</code><dd>Show the current value of the <code>multiple-symbols</code> setting. 
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