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<title>Chapter 5. Questions & 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) V2.10"><link rel="up" href="pt01.html" title="Part I. User' guide"><link rel="prev" href="ch04s05.html" title="Compilers corner"><link rel="next" href="ch06.html" title="Chapter 6. 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 5. Questions & Answers</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s05.html">Prev</a> </td><th width="60%" align="center">Part I. User' guide</th><td width="20%" align="right"> <a accesskey="n" href="ch06.html">Next</a></td></tr></table><hr></div><div class="chapter" title="Chapter 5. Questions & Answers"><div class="titlepage"><div><div><h2 class="title"><a name="d0e3867"></a>Chapter 5. Questions & 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 “too few” or “too many” 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: ”error
C2977: 'boost::mpl::vector' : too many template arguments”? </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….hpp and
a mpl/map60/70….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> </td><td width="20%" align="center"><a accesskey="u" href="pt01.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="ch06.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top"> Compilers corner </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 6. Internals</td></tr></table></div></body></html>
