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POConstant correctness
 

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  1. POConstant correctness
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    <p>In the printMessage if you access the vector of a constant class using the index it works fine, but not with the the iterator (*itr). If the iterator is declared as constant_iterator then it works fine.</p> <p>Why? </p> <p>In both cases I am reading the data and not modifying the vector. Can someone shed some light? </p> <pre><code> #include &lt;iostream&gt; #include &lt;vector&gt; #include &lt;sstream&gt; //Set this define to enable the block to compile. #define WILL_WORK 1 #define WILL_NOT_WORK !WILL_WORK class TestMessage { public: TestMessage(){}; typedef std::vector&lt;int&gt; TestVec; typedef std::vector&lt;int&gt;::iterator TestItr; //The const iterator will work //typedef std::vector&lt;uint32_t&gt;::const_iterator TestItr; typedef std::vector&lt;int&gt;::size_type TestSize; TestVec m_testVector; }; void printMessage(const TestMessage &amp; tmessage) { std::ostringstream asciiMessage; asciiMessage &lt;&lt; tmessage.m_testVector.size() &lt;&lt; ","; #if WILL_NOT_WORK //This will not work // MS Visual Studio // error C2440: 'initializing' : cannot convert from // 'std::_Vector_const_iterator&lt;_Ty,_Alloc&gt;' to // 'std::_Vector_iterator&lt;_Ty,_Alloc&gt;' // GCC // error: conversion from // '__gnu_cxx::__normal_iterator&lt;const int*, // std::vector&lt;int, std::allocator&lt;int&gt; &gt; &gt;' // to non-scalar type // '__gnu_cxx::__normal_iterator&lt;int*, // std::vector&lt;int, std::allocator&lt;int&gt; &gt; &gt;' // requested for (TestMessage::TestItr itr = tmessage.m_testVector.begin(); itr != tmessage.m_testVector.end(); ++itr) { asciiMessage &lt;&lt; *itr; } #endif #if WILL_WORK // This will work for(TestMessage::TestSize index = 0; index &lt; tmessage.m_testVector.size(); ++index) { asciiMessage &lt;&lt; tmessage.m_testVector[index] &lt;&lt; ","; } #endif asciiMessage &lt;&lt; std::endl; std::cout &lt;&lt; asciiMessage.str(); } int main() { TestMessage message; message.m_testVector.push_back(10); message.m_testVector.push_back(20); message.m_testVector.push_back(30); message.m_testVector.push_back(40); printMessage(message); return 0; } </code></pre>
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    1. PTQuestion
    1. USMichael Myers
    1. USschakkere
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    1. PO
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    2. PO
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    3. PO
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    1. VO
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      1. VTUpMod
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