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109 lines
2.4 KiB
C++
109 lines
2.4 KiB
C++
#include <cassert>
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#include <iostream>
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#include <memory>
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#include <vector>
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// From Wikipedia.
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void shared_ptr() {
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std::cout << __FUNCTION__ << std::endl;
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std::shared_ptr<int> p1(new int(5));
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std::shared_ptr<int> p2 = p1; // Both now own the memory.
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assert(p1.use_count() == 2);
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// Memory still exists, due to p2:
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p1.reset();
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assert(p1.get() == NULL && p2.get() != NULL);
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assert(p2.use_count() == 1);
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assert(p1.use_count() == 0);
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// Deletes the memory, since no one else owns the memory.
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p2.reset();
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assert(p1.get() == NULL && p2.get() == NULL);
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assert(p2.use_count() == 0);
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assert(p1.use_count() == 0);
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}
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void shared_ptr_container() {
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std::cout << __FUNCTION__ << std::endl;
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std::shared_ptr<int> p1(new int(5));
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std::shared_ptr<int> p2 = p1; // Both now own the memory.
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assert(p1.use_count() == 2);
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std::vector<std::shared_ptr<int>> v;
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v.push_back(p1);
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v.push_back(p1);
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assert(p1.use_count() == 4);
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p2.reset();
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assert(p1.use_count() == 3);
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assert(p2.use_count() == 0);
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v.pop_back();
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v.pop_back();
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assert(p1.use_count() == 1);
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}
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void weak_ptr() {
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std::cout << __FUNCTION__ << std::endl;
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std::shared_ptr<int> p1(new int(5));
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std::weak_ptr<int> wp1 = p1; // p1 owns the memory.
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{
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std::shared_ptr<int> p2 = wp1.lock(); // Now p1 and p2 own the memory.
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assert(p2 != NULL);
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if (p2) { // As p2 is initialized from a weak pointer,
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// you have to check if the memory still exists!
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// Do something with p2
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}
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} // p2 is destroyed. Memory is owned by p1.
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assert(wp1.lock() != NULL);
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assert(wp1.use_count() == 1);
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p1.reset(); // Memory is deleted.
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assert(wp1.lock() == NULL);
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assert(wp1.use_count() == 0);
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std::shared_ptr<int> p3 = wp1.lock();
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// Memory is gone, so we get an empty shared_ptr.
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assert(p3 == NULL);
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if (p3) {
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// Will not execute this.
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}
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}
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void add_one(std::shared_ptr<int> i) {
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(*i)++;
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}
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void make_shared() {
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std::cout << __FUNCTION__ << std::endl;
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std::shared_ptr<int> sp = std::shared_ptr<int>(new int(12));
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assert(*sp == 12);
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add_one(sp);
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assert(*sp == 13);
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auto sp2 = std::shared_ptr<int>(new int(12));
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assert(*sp2 == 12);
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add_one(sp2);
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add_one(sp2);
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add_one(sp2);
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assert(*sp2 == 15);
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auto sp3 = std::make_shared<int>(12);
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assert(*sp3 == 12);
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add_one(sp3);
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add_one(sp3);
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assert(*sp3 == 14);
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}
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int main() {
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shared_ptr();
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shared_ptr_container();
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weak_ptr();
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make_shared();
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}
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