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<a name="GDB_002fMI-Development-and-Front-Ends"></a>
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<hr>
<a name="GDB_002fMI-Development-and-Front-Ends-1"></a>
<h3 class="section">27.4 <small>GDB/MI</small> Development and Front Ends</h3>
<a name="index-GDB_002fMI-development"></a>

<p>The application which takes the MI output and presents the state of the
program being debugged to the user is called a <em>front end</em>.
</p>
<p>Since <small>GDB/MI</small> is used by a variety of front ends to <small>GDB</small>, changes
to the MI interface may break existing usage.  This section describes how the
protocol changes and how to request previous version of the protocol when it
does.
</p>
<p>Some changes in MI need not break a carefully designed front end, and
for these the MI version will remain unchanged.  The following is a
list of changes that may occur within one level, so front ends should
parse MI output in a way that can handle them:
</p>
<ul>
<li> New MI commands may be added.

</li><li> New fields may be added to the output of any MI command.

</li><li> The range of values for fields with specified values, e.g.,
<code>in_scope</code> (see <a href="GDB_002fMI-Variable-Objects.html#g_t_002dvar_002dupdate">-var-update</a>) may be extended.


</li></ul>

<p>If the changes are likely to break front ends, the MI version level
will be increased by one.  The new versions of the MI protocol are not compatible
with the old versions.  Old versions of MI remain available, allowing front ends
to keep using them until they are modified to use the latest MI version.
</p>
<p>Since <code>--interpreter=mi</code> always points to the latest MI version, it is
recommended that front ends request a specific version of MI when launching
<small>GDB</small> (e.g. <code>--interpreter=mi2</code>) to make sure they get an
interpreter with the MI version they expect.
</p>
<p>The following table gives a summary of the released versions of the MI
interface: the version number, the version of GDB in which it first appeared
and the breaking changes compared to the previous version.
</p>
<table>
<thead><tr><th width="5%">MI version</th><th width="5%">GDB version</th><th width="90%">Breaking changes</th></tr></thead>
<tr><td width="5%"><div align="center">1
</div></td><td width="5%"><div align="center">5.1
</div></td><td width="90%">None</td></tr>
<tr><td width="5%"><div align="center">2
</div></td><td width="5%"><div align="center">6.0
</div></td><td width="90%"><ul>
<li> The <code>-environment-pwd</code>, <code>-environment-directory</code> and
<code>-environment-path</code> commands now returns values using the MI output
syntax, rather than CLI output syntax.

</li><li> <code>-var-list-children</code>&rsquo;s <code>children</code> result field is now a list, rather
than a tuple.

</li><li> <code>-var-update</code>&rsquo;s <code>changelist</code> result field is now a list, rather than
a tuple.
</li></ul></td></tr>
<tr><td width="5%"><div align="center">3
</div></td><td width="5%"><div align="center">9.1
</div></td><td width="90%"><ul>
<li> The output of information about multi-location breakpoints has changed in the
responses to the <code>-break-insert</code> and <code>-break-info</code> commands, as well
as in the <code>=breakpoint-created</code> and <code>=breakpoint-modified</code> events.
The multiple locations are now placed in a <code>locations</code> field, whose value
is a list.
</li></ul></td></tr>
</table>

<p>If your front end cannot yet migrate to a more recent version of the
MI protocol, you can nevertheless selectively enable specific features
available in those recent MI versions, using the following commands:
</p>
<dl compact="compact">
<dt><code>-fix-multi-location-breakpoint-output</code></dt>
<dd><p>Use the output for multi-location breakpoints which was introduced by
MI 3, even when using MI versions 2 or 1.  This command has no
effect when using MI version 3 or later.
</p>
</dd>
</dl>

<p>The best way to avoid unexpected changes in MI that might break your front
end is to make your project known to <small>GDB</small> developers and
follow development on <a href="mailto:gdb@sourceware.org">gdb@sourceware.org</a> and
<a href="mailto:gdb-patches@sourceware.org">gdb-patches@sourceware.org</a>.
<a name="index-mailing-lists"></a>
</p>
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Next: <a href="GDB_002fMI-Output-Records.html#GDB_002fMI-Output-Records" accesskey="n" rel="next">GDB/MI Output Records</a>, Previous: <a href="GDB_002fMI-Compatibility-with-CLI.html#GDB_002fMI-Compatibility-with-CLI" accesskey="p" rel="prev">GDB/MI Compatibility with CLI</a>, Up: <a href="GDB_002fMI.html#GDB_002fMI" accesskey="u" rel="up">GDB/MI</a> &nbsp; [<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>
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