C++中的统一初始化-yiteyi-C++库

统一初始化是C++ 11中的一个特性，它允许使用一致的语法来初始化从原始类型到集合的变量和对象。换句话说，它引入了大括号初始化，它使用大括号（{}）来封装初始值设定项值。语法如下：

null

type var_name{arg1, arg2, ....arg n}

以下是初始化不同类型的不同方法的一些示例：

// uninitialized built-in typeint i;    // initialized built-in typeint j=10; // initialized built-in typeint k(10);// Aggregate initializationint a[]={1, 2, 3, 4} // default constructorX x1; // Parameterized constructorX x2(1); // Parameterized constructor with single argumentX x3=3; // copy-constructorX x4=x3;

如果使用大括号初始化进行初始化，上述代码可以重新编写为：

int i{};     // initialized built-in type, equals to int i{0};int j{10}; // initialized built-in typeint a[]{1, 2, 3, 4} // Aggregate initializationX x1{}; // default constructorX x2{1}; // Parameterized constructor;X x4{x3}; // copy-constructor

统一初始化的应用

动态分配数组的初始化 :

C++

                         // C++ program to demonstrate initialization                       
                         // of dynamic array in C++ using uniform initialization                       
                         #include <bits/stdc++.h>                       
                         using                                     namespace                                     std;                       
                         int                                     main()                       
                         {                       
                                                 // declaring a dynamic array                       
                                                 // and initializing using braces                       
                                                 int                                     * pi =                                     new                                     int                                     [5]{ 1, 2, 3, 4, 5 };                       
           
                                                 // printing the contents of the array                       
                                                 for                                     (                                     int                                     i = 0; i < 5; i++)                       
                                                 cout << *(pi + i) <<                                     " "                                     ;                       
                         }                       

输出

1 2 3 4 5

初始化类的数组数据成员 :

C++

                         // C++ program to initialize                       
                         //  an array data member of a class                       
                         // with uniform initialization                       
                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         class                                     A                       
                         {                       
                                                 int                                     arr[3];                       
           
                         public                                     :                       
                                                 // initializing array using                       
                                                 // uniform initialization                       
                                                 A(                                     int                                     x,                                     int                                     y,                                     int                                     z)                       
                                                 : arr{ x, y, z } {};                       
           
                                                 void                                     show()                       
                                                 {                       
                                                 // printing the contents of the array                       
                                                 for                                     (                                     int                                     i = 0; i < 3; i++)                       
                                                 cout << *(arr + i) <<                                     " "                                     ;                       
                                                 }                       
                         };                       
           
                         // Driver Code                       
                         int                                     main()                       
                         {                       
                                                 // New object created and the numbers                       
                                                 // to initialize the array with, are passed                       
                                                 // into it as arguments                       
                                                 A a(1, 2, 3);                       
                                                 a.show();                       
                                                 return                                     0;                       
                         }                       

输出

1 2 3

隐式初始化要返回的对象 :

C++

                         // C++ program to implicitly                       
                         // initialize an object to return                       
                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         // declaring a class 'A'                       
                         class                                     A {                       
                                                 // a and b are data members                       
                                                 int                                     a;                       
                                                 int                                     b;                       
           
                                                 // constructor                       
                         public                                     :                       
                                                 A(                                     int                                     x,                                     int                                     y)                       
                                                 : a(x)                       
                                                 , b(y)                       
                                                 {                       
                                                 }                       
                                                 void                                     show() { cout << a <<                                     " "                                     << b; }                       
                         };                       
           
                         A f(                                     int                                     a,                                     int                                     b)                       
                         {                       
                                                 // The compiler automatically                       
                                                 // deduces that the constructor                       
                                                 // of the class A needs to be called                       
                                                 // and the function parameters of f are                       
                                                 // needed to be passed here                       
                                                 return                                     { a, b };                       
                         }                       
           
                         // Driver Code                       
                         int                                     main()                       
                         {                       
                                                 A x = f(1, 2);                       
                                                 x.show();                       
                                                 return                                     0;                       
                         }                       

输出

1 2

隐式初始化函数参数

C++

                         // C++ program to demonstrate how to                       
                         // initialize a function parameter                       
                         // using Uniform Initialization                       
           
                         #include <iostream>                       
                         using                                     namespace                                     std;                       
           
                         // declaring a class 'A'                       
                         class                                     A {                       
           
                                                 // a and b are data members                       
                                                 int                                     a;                       
                                                 int                                     b;                       
           
                         public                                     :                       
                                                 A(                                     int                                     x,                                     int                                     y)                       
                                                 : a(x)                       
                                                 , b(y)                       
                                                 {                       
                                                 }                       
                                                 void                                     show() { cout << a <<                                     " "                                     << b; }                       
                         };                       
           
                         void                                     f(A x) { x.show(); }                       
           
                         // Driver Code                       
                         int                                     main()                       
                         {                       
           
                                                 // calling function and initializing it's argument                       
                                                 // using brace initialization                       
                                                 f({ 1, 2 });                       
                                                 return                                     0;                       
                         }                       

输出

1 2

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