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POStrange error regarding STL vector of pointers
 

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  1. POStrange error regarding STL vector of pointers
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    <p>I've a small code snippet which produces an error on running. The following code stores data of mystruct and creates a vector of pointers which store the addresses of the corresponding data.</p> <pre><code>struct mystruct{ std::vector &lt; int &gt; someinfo; int somenumbers; double *somepointer; double someparm; void Print(){....} }; void DoSomething(mystruct &amp;_somestruct, std::vector&lt; mystruct &gt; &amp;_somevec, std::vector&lt;mystruct *&gt; &amp;_ptr){ _somevec.push_back(_somestruct); _ptr.push_back(&amp;(_somevec.back())); } void ReadStruct(){ std::vector&lt;mystruct &gt; _vec; std::vector&lt;mystruct *&gt; _ptr; for(int i=0;i&lt;100;i++){ mystruct _struct; _struct.somenumbers = 3; _struct.someinfo.push_back(0); _struct.someinfo.push_back(1); _struct.someinfo.push_back(2); DoSomething(_struct, _vec, _ptr); } _vec[0].Print(); //Prints correctly _ptr[0]-&gt;Print();//Prints garbage info } </code></pre> <p>If I first create the vector and then create the vector of pointers then the code works perfectly i.e.</p> <pre><code>void DoSomething(mystruct &amp;_somestruct, std::vector&lt; mystruct &gt; &amp;_somevec){ _somevec.push_back(_somestruct); //_ptr.push_back(&amp;(_somevec.back())); } void DoSomething1(std::vector&lt; mystruct &gt; &amp;_somevec, std::vector&lt;mystruct *&gt; &amp;_ptr){ for(int i=0;i&lt;_somevec.size();i++) _ptr.push_back(&amp;(_somevec[i])); } </code></pre> <p>I do not know what mistake I am doing. Your help/inputs is greatly appreciated!!</p>
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    1. USSuman Vajjala
    1. USSuman Vajjala
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    1. COPlease indent your code so that it's readable. Thanks.
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      1. USOliver Charlesworth
    2. COthe pointer version is undefined behavior, as `_struct` is out of scope and destructed after each iteration of the loop, the non pointer version works by copying the struct.
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      1. POStrange error regarding STL vector of pointers
      1. USMgetz
    3. COpossible duplicate of [Strange behaviour with a vector of pointers](http://stackoverflow.com/questions/15899040/strange-behaviour-with-a-vector-of-pointers)
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