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   <title>Chapter&nbsp;5.&nbsp;Questions &amp; Answers</title><link rel="stylesheet" href="boostbook.css" type="text/css"><meta name="generator" content="DocBook XSL-NS Stylesheets V1.75.2"><link rel="home" href="index.html" title="Meta State Machine (MSM) V2.12"><link rel="up" href="pt01.html" title="Part&nbsp;I.&nbsp;User' guide"><link rel="prev" href="ch04s05.html" title="Compilers corner"><link rel="next" href="ch06.html" title="Chapter&nbsp;6.&nbsp;Internals"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter&nbsp;5.&nbsp;Questions &amp; Answers</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s05.html">Prev</a>&nbsp;</td><th width="60%" align="center">Part&nbsp;I.&nbsp;User' guide</th><td width="20%" align="right">&nbsp;<a accesskey="n" href="ch06.html">Next</a></td></tr></table><hr></div><div class="chapter" title="Chapter&nbsp;5.&nbsp;Questions &amp; Answers"><div class="titlepage"><div><div><h2 class="title"><a name="d0e2587"></a>Chapter&nbsp;5.&nbsp;Questions &amp; Answers</h2></div></div></div><p><span class="underline">Question</span>: on_entry gets as argument, the
                sent event. What event do I get when the state becomes default-activated (because it
                is an initial state)?</p><p>
                <span class="underline">Answer</span>: To allow you to know that the state
                was default-activated, MSM generates a boost::msm::InitEvent default event. </p><p><span class="underline">Question</span>: Why do I see no call to
                no_transition in my submachine? </p><p><span class="underline">Answer</span>: Because of the priority rule defined
                by UML. It says that in case of transition conflict, the most inner state has a
                higher priority. So after asking the inner state, the containing composite has to be
                also asked to handle the transition and could find a possible transition.</p><p><span class="underline">Question</span>: Why do I get a compile error
                saying the compiler cannot convert to a function ...Fsm::*(some_event)? </p><p><span class="underline">Answer</span>: You probably defined a transition
                triggered by the event some_event, but used a guard/action method taking another
                event. </p><p><span class="underline">Question</span>: Why do I get a compile error
                saying something like &#8220;too few&#8221; or &#8220;too many&#8221; template arguments? </p><p><span class="underline">Answer</span>: You probably defined a transition in
                form of a a_row or g_row where you wanted just a _row or the other way around. With
                Row, it could mean that you forgot a "none". </p><p><span class="underline">Question</span>: Why do I get a very long compile
                error when I define more than 20 rows in the transition table? </p><p><span class="underline">Answer</span>: MSM uses Boost.MPL under the hood
                and this is the default maximum size. Please define the following 3 macros before
                including any MSM headers: </p><pre class="programlisting">#define BOOST_MPL_CFG_NO_PREPROCESSED_HEADERS
#define BOOST_MPL_LIMIT_VECTOR_SIZE 30 // or whatever you need               
#define BOOST_MPL_LIMIT_MAP_SIZE 30 // or whatever you need </pre><p><span class="underline">Question</span>: Why do I get this error: &#8221;error
                C2977: 'boost::mpl::vector' : too many template arguments&#8221;? </p><p><span class="underline">Answer</span>: The first possibility is that you
                defined a transition table as, say, vector17 and have 18 entries. The second is that
                you have 17 entries and have a composite state. Under the hood, MSM adds a row for
                every event in the composite transition table. The third one is that you used a
                mpl::vector without the number of entries but are close to the MPL default of 50 and
                have a composite, thus pushing you above 50. Then you need mpl/vector60/70&#8230;.hpp and
                a mpl/map60/70&#8230;.hpp </p><p><span class="underline">Question</span>: Why do I get a very long compile
                error when I define more than 10 states in a state machine? </p><p><span class="underline">Answer</span>: MSM uses Boost.Fusion under the hood
                and this is the default maximum size. Please define the following macro before
                including any MSM headers: </p><pre class="programlisting">#define FUSION_MAX_VECTOR_SIZE 20 // or whatever you need </pre></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="ch04s05.html">Prev</a>&nbsp;</td><td width="20%" align="center"><a accesskey="u" href="pt01.html">Up</a></td><td width="40%" align="right">&nbsp;<a accesskey="n" href="ch06.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> Compilers corner &nbsp;</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">&nbsp;Chapter&nbsp;6.&nbsp;Internals</td></tr></table></div></body></html>