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POWhat is the correct syntax to construct a class with a shared_ptr as member field?
 

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  1. POWhat is the correct syntax to construct a class with a shared_ptr as member field?
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    <p>Suppose, I want to make a class <code>B</code> with a pointer to another class <code>A</code>. In the constructor of <code>A</code> I want to construct <code>B</code> and passing it a pointer to <code>this</code>. In principle, this pointer can be a <code>shared_ptr</code>, correct? Then how do I make such a class with the assignment of the <code>shared_ptr</code> in the constructor?</p> <p>I tried it in the code below. <code>ClassB</code> and <code>ClassC</code> are identical, with a pointer to <code>ClassA</code> which constructs instances of <code>ClassB</code> and <code>ClassC</code>. The only two differences are that <code>ClassB</code> holds a regular pointer and <code>ClassC</code> holds a <code>shared_ptr</code> to <code>ClassA</code> and that the code with <code>ClassB</code> is working and the code with <code>ClassC</code> is not. What am I doing wrong?</p> <pre><code>// Main.cpp : Defines the entry point for the console application. #include "ClassA.h" #include &lt;iostream&gt; int main(int argc, char* argv[]) { std::cout &lt;&lt; "Create B and C separately, without a reference to A:" &lt;&lt; std::endl; ClassB(nullptr); ClassC(nullptr); std::cout &lt;&lt; "Create A, and through it B and C:" &lt;&lt; std::endl; ClassA A; A.PrintHello(); A.getObjectB().getPointerToA()-&gt;PrintHello(); A.PrintHello(); A.getObjectC().getPointerToA()-&gt;PrintHello(); return 0; } // ClassA.h #pragma once #include "ClassB.h" #include "ClassC.h" class ClassA { private: ClassB objectB; ClassC objectC; public: ClassA(void); ClassB getObjectB() { return objectB; }; ClassC getObjectC() { return objectC; }; void PrintHello(); }; // ClassA.cpp #include "ClassA.h" #include &lt;iostream&gt; #include &lt;memory&gt; ClassA::ClassA(void) : objectB(ClassB( this )), objectC(ClassC( std::make_shared&lt;ClassA&gt;(*this) )) { std::cout &lt;&lt; "Class A fully constructed" &lt;&lt; std::endl; } void ClassA::PrintHello() { std::cout &lt;&lt; "Hello" &lt;&lt; std::endl; } // ClassB.h #pragma once #include &lt;memory&gt; class ClassA; class ClassB { private: ClassA* pointerToA; public: ClassB(ClassA* pA); ClassA* getPointerToA() { return pointerToA; }; }; // ClassB.cpp #include "ClassB.h" #include &lt;iostream&gt; ClassB::ClassB(ClassA* pA) : pointerToA(pA) { std::cout &lt;&lt; "Class B constructed" &lt;&lt; std::endl; } // ClassC.h #pragma once #include &lt;memory&gt; class ClassA; class ClassC { private: std::shared_ptr&lt;ClassA&gt; pointerToA; public: ClassC(std::shared_ptr&lt;ClassA&gt; pA); std::shared_ptr&lt;ClassA&gt; getPointerToA() { return pointerToA; }; }; // ClassC.cpp #include "ClassC.h" #include &lt;iostream&gt; ClassC::ClassC(std::shared_ptr&lt;ClassA&gt; pA) : pointerToA(pA) { std::cout &lt;&lt; "Class C constructed" &lt;&lt; std::endl; } </code></pre>
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