Created
July 27, 2013 00:14
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A simple example demonstrating C++ virtual destructors and the pitfalls if they are not used.
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/** An example of a virtual destructor. | |
* | |
* Compile with: | |
* g++ -Wall test_cpp_virtual_destructor.cpp -o test_cpp_virtual_destructor | |
*/ | |
#include <iostream> | |
using namespace std; | |
/// A class with a non-virtual destructor. | |
struct NonVirtualDestructor | |
{ | |
~NonVirtualDestructor(void) | |
{ | |
cout << "NonVirtualDestructor::~NonVirtualDestructor" << endl; | |
} | |
// Simple method to allow us to do something with the class instance. | |
// Otherwise compiler might optimize out. | |
void Foo(void) | |
{ | |
cout << "NonVirtualDestructor::Foo" << endl; | |
} | |
}; | |
/// A class derived from a base class with non-virtual destructor. | |
struct DerivedNonVirtualDestructor : NonVirtualDestructor | |
{ | |
~DerivedNonVirtualDestructor(void) | |
{ | |
cout << "DerivedNonVirtualDestructor::~DerivedNonVirtualDestructor" << endl; | |
} | |
}; | |
/// A class with a virtual destructor. | |
struct VirtualDestructor | |
{ | |
virtual ~VirtualDestructor(void) | |
{ | |
cout << "VirtualDestructor::~VirtualDestructor" << endl; | |
} | |
// Simple method to allow us to do something with the class instance. | |
// Otherwise compiler might optimize out. | |
void Foo(void) | |
{ | |
cout << "VirtualDestructor::Foo" << endl; | |
} | |
}; | |
/// A class derived from a base class with virtual destructor. | |
struct DerivedVirtualDestructor : VirtualDestructor | |
{ | |
// Note, that destructor is not defined with explicit virtual keyword. | |
// It will still be virtual because base class destructor is virtual. | |
~DerivedVirtualDestructor(void) | |
{ | |
cout << "DerivedVirtualDestructor::~DerivedVirtualDestructor" << endl; | |
} | |
}; | |
// Test DerivedNonVirtualDestructor in a local scope. | |
// Destructors are called for derived and base class. | |
// Expect output: | |
// NonVirtualDestructor::Foo | |
// DerivedNonVirtualDestructor::~DerivedNonVirtualDestructor | |
// NonVirtualDestructor::~NonVirtualDestructor | |
void test_DerivedNonVirtualDestructor_in_local_scope(void) | |
{ | |
cout << endl << __FUNCTION__ << endl; | |
DerivedNonVirtualDestructor c; | |
c.Foo(); | |
} | |
// Test DerivedVirtualDestructor in a local scope. | |
// Destructors are called for derived and base class. | |
// Expect output: | |
// VirtualDestructor::Foo | |
// DerivedVirtualDestructor::~DerivedVirtualDestructor | |
// VirtualDestructor::~VirtualDestructor | |
void test_DerivedVirtualDestructor_in_local_scope(void) | |
{ | |
cout << endl << __FUNCTION__ << endl; | |
DerivedVirtualDestructor c; | |
c.Foo(); | |
} | |
// Test dynamically allocated DerivedNonVirtualDestructor. | |
// Destructors are called for base class BUT NOT DERIVED CLASS! | |
// If the derived class had allocated new memory, the destructor would not be called | |
// in order to delete the memory. This could cause memory leaks! | |
// | |
// Expect output: | |
// NonVirtualDestructor::Foo | |
// NonVirtualDestructor::~NonVirtualDestructor | |
// | |
void test_DerivedNonVirtualDestructor_in_dynamic_memory(void) | |
{ | |
cout << endl << __FUNCTION__ << endl; | |
NonVirtualDestructor* c = new DerivedNonVirtualDestructor(); | |
c->Foo(); | |
delete c; | |
} | |
// Test dynamically allocated DerivedVirtualDestructor. | |
// Destructors are called for base class and derived class. | |
// This is most often the desired behavior. | |
// | |
// Expect output: | |
// VirtualDestructor::Foo | |
// DerivedVirtualDestructor::~DerivedVirtualDestructor | |
// VirtualDestructor::~VirtualDestructor | |
// | |
void test_DerivedVirtualDestructor_in_dynamic_memory(void) | |
{ | |
cout << endl << __FUNCTION__ << endl; | |
VirtualDestructor* c = new DerivedVirtualDestructor(); | |
c->Foo(); | |
delete c; | |
} | |
int main(int argc, const char* argv[]) | |
{ | |
test_DerivedNonVirtualDestructor_in_local_scope(); | |
test_DerivedVirtualDestructor_in_local_scope(); | |
test_DerivedNonVirtualDestructor_in_dynamic_memory(); | |
test_DerivedVirtualDestructor_in_dynamic_memory(); | |
} |
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