提交第3题

src/群友提交/第03题/TEST.ixx

@@ -0,0 +1,76 @@
+#define _CRT_SECURE_NO_WARNINGS
+
+#include <cstdio>
+#include <cassert>
+#include <stdexcept>
+#include <iostream>
+#include <functional>
+
+struct X {
+    X() { puts("X()"); }
+    X(const X&) { puts("X(const X&)"); }
+    X(X&&) noexcept { puts("X(X&&)"); }
+    ~X() { puts("~X()"); }
+};
+
+template <typename F, typename... Args>
+class scope_guard {
+public:
+	scope_guard(F&& f, Args&&... args) : f_(std::forward<F>(f)), args_(std::forward<Args>(args)...) {}
+	~scope_guard() {
+		std::apply(f_, args_);
+	}
+private:
+    F f_;
+	std::tuple<Args...> args_;
+};
+
+template <typename F, typename... Args>
+scope_guard(F&& f, Args&&... args) -> scope_guard<F, Args...>;
+
+int main() {
+    {
+        // scope_guard的作用之一，是让各种C风格指针接口作为局部变量时也能得到RAII支持
+        // 这也是本题的基础要求
+        FILE* fp = nullptr;
+        try {
+            fp = fopen("test.txt", "a");
+            auto guard = scope_guard([&] {
+                fclose(fp);
+                fp = nullptr;
+                });
+
+            throw std::runtime_error{"Test"};
+        }
+        catch (std::exception& e) {
+            puts(e.what());
+        }
+        assert(fp == nullptr);
+    }
+    puts("----------");
+    {
+        // 附加要求1，支持函数对象调用
+        struct Test {
+            void operator()(X* x) {
+                delete x;
+            }
+        } t;
+        auto x = new X{};
+        auto guard = scope_guard(t, x);
+    }
+    puts("----------");
+    {
+        // 附加要求2，支持成员函数和std::ref
+        auto x = new X{};
+        {
+            struct Test {
+                void f(X*& px) {
+                    delete px;
+                    px = nullptr;
+                }
+            } t;
+            auto guard = scope_guard{ &Test::f, &t, std::ref(x) };
+        }
+        assert(x == nullptr);
+    }
+}