└── shared_ptr.cpp


/shared_ptr.cpp:
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  1 | #include <iostream>
  2 | #include <memory>
  3 | #include <vector>
  4 | #include <thread>
  5 | #include <atomic>
  6 | 
  7 | void AdvancedSharedPtr();                   // Forward reference
  8 | void FileExample();                         // Forward reference
  9 | void WeakPtrDemo();                         // Forward reference
 10 | 
 11 | class Base {
 12 | public:
 13 |     virtual void speak() {
 14 |         std::cout << "I am a Base." << std::endl;
 15 |     }
 16 | 
 17 |     virtual ~Base() {
 18 |         std::cout << "Base destroyed." << std::endl;
 19 |     }
 20 | };
 21 | 
 22 | class Derived : public Base {
 23 | public:
 24 |     void speak() override {
 25 |         std::cout << "I am a Derived." << std::endl;
 26 |     }
 27 | 
 28 |     ~Derived() override {
 29 |         std::cout << "Derived destroyed." << std::endl;
 30 |     }
 31 | };
 32 | 
 33 | void custom_deleter(Base *ptr) {
 34 |     std::cout << "Custom deleter called." << std::endl;
 35 |     delete ptr;
 36 | }
 37 | 
 38 | int main() 
 39 | {
 40 |     // Creating a shared_ptr and initializing it with a new object
 41 |     std::shared_ptr<Base> sp1 = std::make_shared<Base>();
 42 |     sp1->speak();
 43 | 
 44 |     // Creating a shared_ptr with a custom deleter
 45 |     std::shared_ptr<Base> sp2(new Derived, custom_deleter);
 46 |     sp2->speak();
 47 | 
 48 |     // Creating a shared_ptr from another shared_ptr (copying)
 49 |     std::shared_ptr<Base> sp3 = sp1;
 50 |     sp3->speak();
 51 | 
 52 |     // Resetting a shared_ptr
 53 |     sp3.reset(new Derived);
 54 |     sp3->speak();
 55 | 
 56 |     // Checking the use_count of a shared_ptr
 57 |     std::cout << "sp1 use_count: " << sp1.use_count() << std::endl;
 58 | 
 59 |     // Using shared_ptr in a container
 60 |     std::vector<std::shared_ptr<Base>> container;
 61 |     container.push_back(sp1);
 62 |     container.push_back(sp2);
 63 |     container.push_back(sp3);
 64 | 
 65 |     for (const auto &item : container) {
 66 |         item->speak();
 67 |     }
 68 | 
 69 |     AdvancedSharedPtr();
 70 |     WeakPtrDemo();
 71 | 
 72 |     return 0;
 73 | }
 74 | 
 75 | //-------------------------------------------------------------------------
 76 | // Advanced shared_ptr examples
 77 | //-------------------------------------------------------------------------
 78 | 
 79 | void AdvancedSharedPtr() 
 80 | {
 81 |     // 1. Weak pointers
 82 |     std::shared_ptr<Base> sp1 = std::make_shared<Base>();
 83 |     std::weak_ptr<Base> wp1 = sp1;
 84 | 
 85 |     if (std::shared_ptr<Base> locked = wp1.lock()) {
 86 |         locked->speak();
 87 |     }
 88 | 
 89 |     sp1.reset();
 90 | 
 91 |     if (wp1.expired()) {
 92 |         std::cout << "The weak_ptr is expired." << std::endl;
 93 |     }
 94 | 
 95 |     // 2. Aliasing constructor
 96 |     std::shared_ptr<Base> sp2 = std::make_shared<Base>();
 97 |     std::shared_ptr<Base> sp2_alias(sp2, sp2.get());
 98 |     sp2_alias->speak();
 99 |     std::cout << "sp2 use_count: " << sp2.use_count() << std::endl;
100 | 
101 |     // 3. shared_ptr for arrays
102 |     std::shared_ptr<Base[]> sp3(new Base[3]);
103 |     sp3[0].speak();
104 |     sp3[1].speak();
105 |     sp3[2].speak();
106 | 
107 |     // 4. Atomic operations
108 |     std::shared_ptr<Base> sp4 = std::make_shared<Base>();
109 |     std::shared_ptr<Base> sp5;
110 | 
111 |     std::thread t1([&]() {
112 |         std::atomic_store(&sp5, std::atomic_load(&sp4));
113 |     });
114 | 
115 |     std::thread t2([&]() {
116 |         std::atomic_store(&sp4, std::shared_ptr<Base>(nullptr));
117 |     });
118 | 
119 |     t1.join();
120 |     t2.join();
121 | 
122 |     if (sp5) {
123 |         sp5->speak();
124 |     }
125 | }
126 | 
127 | //-------------------------------------------------------------------------
128 | // Custom deleter example for FILE objects
129 | //-------------------------------------------------------------------------
130 | 
131 | void file_deleter(FILE *file) {
132 |     if (file) {
133 |         std::cout << "Closing the file." << std::endl;
134 |         fclose(file);
135 |     }
136 | }
137 | 
138 | void readFile(const char *filename) {
139 |     // Create a shared_ptr with a custom deleter
140 |     std::shared_ptr<FILE> file(fopen(filename, "r"), file_deleter);
141 | 
142 |     if (!file) {
143 |         std::cerr << "Failed to open the file." << std::endl;
144 |         return;
145 |     }
146 | 
147 |     // Read the file
148 |     char buffer[256];
149 |     while (fgets(buffer, sizeof(buffer), file.get()) != nullptr) {
150 |         std::cout << buffer;
151 |     }
152 | 
153 |     // The file will be closed automatically by the custom deleter
154 | }
155 | 
156 | void FileExample()
157 | {
158 |     readFile("main.cpp");
159 | }
160 | 
161 | //-------------------------------------------------------------------------
162 | // Weak pointer demo
163 | //-------------------------------------------------------------------------
164 | 
165 | void WeakPtrDemo() 
166 | {
167 |     // Create a shared_ptr and initialize it with a new object
168 |     std::shared_ptr<Base> sp1 = std::make_shared<Derived>();
169 | 
170 |     // Create a weak_ptr from the shared_ptr
171 |     std::weak_ptr<Base> wp1(sp1);
172 | 
173 |     // Check if the weak_ptr is valid and lock it to obtain a shared_ptr
174 |     if (auto locked = wp1.lock()) {
175 |         std::cout << "Weak pointer is valid. Locked and obtained shared_ptr." << std::endl;
176 |         locked->speak();
177 |     } else {
178 |         std::cout << "Weak pointer is not valid." << std::endl;
179 |     }
180 | 
181 |     // Reset the shared_ptr, causing the object to be destroyed
182 |     sp1.reset();
183 | 
184 |     // Check if the weak_ptr is still valid
185 |     if (wp1.expired()) {
186 |         std::cout << "Weak pointer is now expired." << std::endl;
187 |     } else {
188 |         std::cout << "Weak pointer is still valid." << std::endl;
189 |     }
190 | }


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