void f(shared_ptr<int>, int);
int g();
void ok()
{
shared_ptr<int> p( new int(2) );
f( p, g() );
}
void bad()
{
f( shared_ptr<int>( new int(2) ), g() );
}
shared_ptr
#include <iostream>
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>
using std::cout;
using std::endl;
struct Base
{
Base() {
cout << "Base::Base()\n";
}
~Base() {
cout << "Base::~Base()\n";
}
};
struct Derived :public Base {
Derived() {
cout << "Derived::Derived()" << endl;
}
~Derived() {
cout << "Dervive::~Derived()" << endl;
}
};
void thr(std::shared_ptr<Base> p) {
std::this_thread::sleep_for(std::chrono::seconds(1));
std::shared_ptr<Base> lp = p;
{
static std::mutex io_mutex;
std::lock_guard<std::mutex> lk(io_mutex);
std::cout << "local pointer in a thread:\n"
<< "lp.get()" << lp.get()
<< ",lp.use_count()" << lp.use_count() << "\n";
}
}
int main() {
std::shared_ptr<Base> p = std::make_shared<Derived>();
std::cout << "Created a shared Derived (as a pointer to Base)\n"
<< "p.get" << p.get()
<< ",p.use_count()= " << p.use_count() << "\n";
std::thread t1(thr, p), t2(thr, p), t3(thr, p);
p.reset(); // release ownership from main
std::cout << "shared ownership between 3 threads and released\n"
<< "ownership from main:\n"
<< "p.get()" << p.get()
<< ",p.use_count()" << p.use_count() << "\n";
t1.join(); t2.join(); t3.join();
std::cout << "All threads completed,the lase one deleted Derived\n";
system("pause");
return 0;
}
