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#include <iostream>
#include <boost/shared_ptr.hpp>
class A {
public :
A ( ) { std :: cout << "in A::A()." << std :: endl ; }
~ A ( ) { std :: cout << "in A::~A()." << std :: endl ; }
} ;
class B {
public :
B ( ) { std :: cout << "in B::B()." << std :: endl ; throw 1024 ; }
~ B ( ) { std :: cout << "in B::~B()." << std :: endl ; }
} ;
class C {
public :
C ( ) : m_a ( new A ) , m_b ( new B ) { }
#ifndef _USE_SHARED_PTR
~ C ( ) { delete m_b ; delete m_a ; }
#endif
private :
#ifndef _USE_SHARED_PTR
A * m_a ;
B * m_b ;
#else
boost :: shared_ptr < A > m_a ;
boost :: shared_ptr < B > m_b ;
#endif
} ;
int main ( ) {
try { C c ; } catch ( . . . ) { }
return 0 ;
}
Output:
binson@binson-precise:~$ g++ ptr.cpp -o ptr
binson@binson-precise:~$ ./ptr
in A::A().
in B::B().
binson@binson-precise:~$ g++ -D_USE_SHARED_PTR ptr.cpp -o ptr
binson@binson-precise:~$ ./ptr
in A::A().
in B::B().
in A::~A().
Exception safety is ensured, when using shared_ptr. Memory allocated by m_a is freed even when an exception is thrown. The trick is: the destructor of class shared_ptr is invoked after the destructor of class C.