Console.WriteLine 中的 {0} 代表什么? [英] What does {0} stands for in Console.WriteLine?

问题描述

给定代码:

// person.cs
using System;

// #if false

class Person
{
    private string myName = "N/A";
    private int myAge = 0;

    // Declare a Name property of type string:
    public string Name
    {
        get
        {
            return myName;
        }
        set
        {
            myName = value;
        }
    }

    // Declare an Age property of type int:
    public int Age
    {
        get
        {
            return myAge;
        }
        set
        {
            myAge = value;
        }
    }

    public override string ToString()
    {
        return "Name = " + Name + ", Age = " + Age;
    }

    public static void Main()
    {
        Console.WriteLine("Simple Properties");

        // Create a new Person object:
        Person person = new Person();

        // Print out the name and the age associated with the person:
        Console.WriteLine("Person details - {0}", person);

        // Set some values on the person object:
        person.Name = "Joe";
        person.Age = 99;
        Console.WriteLine("Person details - {0}", person);

        // Increment the Age property:
        person.Age += 1;
        Console.WriteLine("Person details - {0}", person);
    }
}

// #endif

代码的输出是:

Simple Properties
Person details - Name = N/A, Age = 0
Person details - Name = Joe, Age = 99
Person details - Name = Joe, Age = 100

Console.WriteLine("Person details - {0}", person); 中的 {0} 代表什么?怎么换成 Name..... 了?

What does the {0} in Console.WriteLine("Person details - {0}", person); stands for ? How come it's replaced by Name..... ?

当我使用 {1} 而不是 {0} 时，我得到一个异常...

When I put {1} instead of {0} I get an exception ...

推荐答案

如您所见，您的 person 对象上有一个返回字符串的代码，控制台检查您的对象上是否存在名称为 ToString 的字符串类型类与否，如果存在则返回你的字符串:

As you can see, There's a code on your person object that returns a string, Console checks for If a type of string with name of ToString exists on your object class or not, If exists then It returns your string:

public override string ToString()
{
     return "Name = " + Name + ", Age = " + Age;
}

并且 {0} 是格式化的消息，当您将其定义为 {0} 时，这意味着打印/格式化您插入到函数的 params 参数中的零索引对象.这是一个从零开始的数字，用于获取您想要的对象的索引，这是一个示例:

And {0} Is a formatted message, When you define It to {0} It means printing/formatting the zero Index object that you Inserted Into params arguments of your function. It's a zero based number that gets the index of object you want, Here's an example:

Console.WriteLine("{0} Is great, {1} Do you think of It? {2} Think {0} Is great!", "C#", "What", "I");

// C# Is great, What do you think of It? I think C# Is great!

当您说 {0} 时，它会获取 C# 或您的对象 [] 的 [0].

When you say {0} It gets C# or the [0] of your object[].

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