mirror of
https://github.com/triqs/dft_tools
synced 2024-12-28 15:15:52 +01:00
92 lines
1.5 KiB
C++
92 lines
1.5 KiB
C++
|
#include <iostream>
|
||
|
#include <boost/shared_ptr.hpp>
|
||
|
|
||
|
|
||
|
class myObject{
|
||
|
|
||
|
int i;
|
||
|
|
||
|
public:
|
||
|
|
||
|
myObject(){}
|
||
|
myObject(int i_):i(i_){}
|
||
|
int getValue() const {return i;}
|
||
|
};
|
||
|
|
||
|
|
||
|
|
||
|
struct A{
|
||
|
|
||
|
|
||
|
};
|
||
|
|
||
|
struct B{
|
||
|
int data;
|
||
|
boost::shared_ptr<A> p;
|
||
|
};
|
||
|
|
||
|
struct C{
|
||
|
boost::shared_ptr<A> p;
|
||
|
};
|
||
|
|
||
|
|
||
|
int main(){
|
||
|
|
||
|
/* WHY POINTERS? */
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
myObject A(0); // object is allocated on the stack
|
||
|
|
||
|
/* stack VS heap */
|
||
|
// small variables on the stack
|
||
|
// dynamical memory on the heap == "new"
|
||
|
|
||
|
//when running, the OS has allocated the stack size...
|
||
|
//when allocatinh by new ==> HEAP, one asks the kernel for space in the system ... takes time!
|
||
|
//RULE: in critical loops, do not allocate using new !
|
||
|
|
||
|
//stack: only for objects whose size is known at compile time
|
||
|
|
||
|
//array lib : minivector on stack, to avoid allocation problems (ulimit...
|
||
|
|
||
|
|
||
|
std::cout << A.getValue()<<std::endl;
|
||
|
|
||
|
/* USUAL POINTERS */
|
||
|
myObject * p1;
|
||
|
p1 = new myObject(1); //allocate on the heap
|
||
|
|
||
|
myObject * p2(new myObject(2)); // shorter way
|
||
|
|
||
|
|
||
|
// two equivalent ways of accessing public members
|
||
|
std::cout << p1->getValue() << std::endl;
|
||
|
std::cout << (*p1).getValue() << std::endl;
|
||
|
|
||
|
|
||
|
|
||
|
/* THE ISSUE */
|
||
|
delete(p1); // deletes the pointer but not the underlying data
|
||
|
|
||
|
|
||
|
|
||
|
/* SHARED POINTER */
|
||
|
boost::shared_ptr<myObject> p1_sh(new myObject(1));
|
||
|
|
||
|
std::cout << p1_sh->getValue()<<std::endl;
|
||
|
|
||
|
boost::shared_ptr<myObject> p2_sh = p1_sh;
|
||
|
|
||
|
std::cout << p2_sh->getValue()<<std::endl;
|
||
|
|
||
|
//never delete it!!
|
||
|
/* difference betw pointer and reference : dynamical polymorphism */
|
||
|
|
||
|
|
||
|
|
||
|
|
||
|
return 0;
|
||
|
}
|