mirror of
https://github.com/triqs/dft_tools
synced 2024-11-01 03:33:50 +01:00
92 lines
1.5 KiB
C++
92 lines
1.5 KiB
C++
#include <iostream>
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#include <boost/shared_ptr.hpp>
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class myObject{
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int i;
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public:
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myObject(){}
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myObject(int i_):i(i_){}
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int getValue() const {return i;}
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};
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struct A{
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};
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struct B{
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int data;
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boost::shared_ptr<A> p;
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};
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struct C{
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boost::shared_ptr<A> p;
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};
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int main(){
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/* WHY POINTERS? */
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myObject A(0); // object is allocated on the stack
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/* stack VS heap */
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// small variables on the stack
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// dynamical memory on the heap == "new"
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//when running, the OS has allocated the stack size...
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//when allocatinh by new ==> HEAP, one asks the kernel for space in the system ... takes time!
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//RULE: in critical loops, do not allocate using new !
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//stack: only for objects whose size is known at compile time
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//array lib : minivector on stack, to avoid allocation problems (ulimit...
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std::cout << A.getValue()<<std::endl;
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/* USUAL POINTERS */
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myObject * p1;
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p1 = new myObject(1); //allocate on the heap
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myObject * p2(new myObject(2)); // shorter way
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// two equivalent ways of accessing public members
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std::cout << p1->getValue() << std::endl;
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std::cout << (*p1).getValue() << std::endl;
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/* THE ISSUE */
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delete(p1); // deletes the pointer but not the underlying data
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/* SHARED POINTER */
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boost::shared_ptr<myObject> p1_sh(new myObject(1));
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std::cout << p1_sh->getValue()<<std::endl;
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boost::shared_ptr<myObject> p2_sh = p1_sh;
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std::cout << p2_sh->getValue()<<std::endl;
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//never delete it!!
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/* difference betw pointer and reference : dynamical polymorphism */
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return 0;
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}
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