update dir

decltype/decltype.cpp

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+/**
+ * @file decltype.cpp
+ * @brief g++ -o decltype decltype.cpp -std=c++11
+ * @author 光城
+ * @version v1
+ * @date 2019-08-08
+ */
+
+#include <iostream>
+#include <vector>
+using namespace std;
+/**
+ * 泛型编程中结合auto，用于追踪函数的返回值类型
+ */
+template <typename T>
+
+auto multiply(T x, T y)->decltype(x*y)
+{
+    return x*y;
+}
+
+int main()
+{
+    int nums[] = {1,2,3,4};
+    vector<int> vec(nums,nums+4);
+    vector<int>::iterator it;
+
+    for(it=vec.begin();it!=vec.end();it++)
+        cout<<*it<<" ";
+    cout<<endl;
+
+
+    using nullptr_t = decltype(nullptr);
+    nullptr_t  nu;
+    int * p =NULL;
+    if(p==nu)
+        cout<<"NULL"<<endl;
+
+
+    typedef decltype(vec.begin()) vectype;
+
+    for(vectype i=vec.begin();i!=vec.end();i++)
+        cout<<*i<<" ";
+    cout<<endl;
+
+    /**
+     * 匿名结构体
+     */
+    struct
+    {
+        int d ;
+        double b;
+    }anon_s;
+
+    decltype(anon_s) as; // 定义了一个上面匿名的结构体
+
+    cout<<multiply(11,2)<<endl;
+
+    return 0;
+}