Как работают методы expired() и lock() у std::weak_ptr.

gusenov · gusenov · commit b0ec903f840e · 2020-05-05T18:55:39.000+06:00
diff --git a/README.md b/README.md
@@ -212,12 +212,18 @@
 
 ## Умные указатели
 
+## std::shared_ptr
+
 - [Сравнение shared_ptr](smart-ptr/shared_ptr/cmp-shared-ptr)
 - [Простейшая реализация shared_from_this функциональности](smart-ptr/shared_ptr/shared-from-this)
 - [Приведение типов умных указателей](smart-ptr/shared_ptr/shared-ptr-casting)
 - [Сброс std::shared_ptr](smart-ptr/shared_ptr/shared-ptr-reset)
 - [Удаление элемента из std::vector<std::shared_ptr<…>>](smart-ptr/shared_ptr/vec-with-shared-ptr-items)
 
+## std::weak_ptr
+
+- [Как работают методы expired() и lock() у std::weak_ptr](smart-ptr/weak_ptr/lock-weak-ptr)
+
 
 # Макросы
 
diff --git a/smart-ptr/weak_ptr/lock-weak-ptr/.gitignore b/smart-ptr/weak_ptr/lock-weak-ptr/.gitignore
@@ -0,0 +1,37 @@
+# ---------------------------------------------------------------------------
+# https://github.com/github/gitignore/blob/master/C++.gitignore
+
+# Prerequisites
+*.d
+
+# Compiled Object files
+*.slo
+*.lo
+*.o
+*.obj
+
+# Precompiled Headers
+*.gch
+*.pch
+
+# Compiled Dynamic libraries
+*.so
+*.dylib
+*.dll
+
+# Fortran module files
+*.mod
+*.smod
+
+# Compiled Static libraries
+*.lai
+*.la
+*.a
+*.lib
+
+# Executables
+*.exe
+*.out
+*.app
+
+# ---------------------------------------------------------------------------
diff --git a/smart-ptr/weak_ptr/lock-weak-ptr/main.cc b/smart-ptr/weak_ptr/lock-weak-ptr/main.cc
@@ -0,0 +1,57 @@
+#include <memory>
+#include <iostream>
+#include <cstdlib>
+
+struct A {
+    virtual ~A() = default;
+
+    virtual void whoami() const = 0;
+};
+
+class B : public A {
+public:
+    B() = default;
+    ~B() override {
+        std::cout << "~B()" << std::endl;
+    }
+
+    void whoami() const override {
+        std::cout << "B" << std::endl;
+    }
+
+private:
+};
+
+
+void test1() {
+    std::weak_ptr<A> w;
+    assert(w.expired());  // TRUE
+    assert(!w.lock());  // TRUE
+    {
+        std::shared_ptr<A> s = std::make_shared<B>();
+        w = s;
+        assert(!w.expired());  // TRUE
+        assert(w.lock());  // TRUE
+    }
+    assert(w.expired());  // TRUE
+    assert(!w.lock());  // TRUE
+}
+
+
+void test2() {
+    std::weak_ptr<A> w;
+    assert(w.expired());  // TRUE
+    auto s = w.lock();
+    assert(!s);  // TRUE
+    s = std::make_shared<B>();
+    assert(s);  // TRUE
+    assert(w.expired());  // TRUE
+}
+
+
+int main(int argc, char const * argv[]) {
+    // test1();
+    test2();
+
+    return EXIT_SUCCESS;
+}
diff --git a/smart-ptr/weak_ptr/lock-weak-ptr/run.sh b/smart-ptr/weak_ptr/lock-weak-ptr/run.sh
@@ -0,0 +1,7 @@
+#!/bin/bash
+
+EXE_FILE="./a.out"
+
+[ -f "$EXE_FILE" ] && rm "$EXE_FILE"
+
+clang++ --std=c++17 main.cc -o "$EXE_FILE" && "$EXE_FILE"
