Detailed introduction to the difference between out and ref in C# (picture and text)

This article mainly introduces the relevant knowledge of out and ref. It has a certain reference value. Let’s take a look at it with the editor.

In order to fully understand C# out and ref, you must first clarify the following two concepts ( If you have a good grasp of value types and reference types, you can skip "1. Clarify two basic concepts")

1. Clarify two basic concepts

Value type:

Definition: Passed by value, that is, the actual parameters are passed to the formal parameters (the terms formal parameters and actual parameters are not defined here).

Storage method: Mainly in the stack.

Essence: Implemented through value transfer, copycopy form, and the Pop() and Push() methods of the call stack.

Common types: int, float, bool, enum, struct, Array, etc.

Value type example:

//主函数
 static void Main(string[] args)
 {
  //定义两个实参n1和n2，并初始化
  int n1 = 10, n2 = 20;
  Console.WriteLine("交换前n1和n2的值");
  Console.WriteLine("n1={0},n2={1}", n1, n2);//n1=10,n2=20
  Swap(n1,n2);
  Console.WriteLine("交换后n1和n2的值");
  Console.WriteLine("n1={0},n2={1}",n1,n2);//n1=10,n2=20
  Console.Read();
 }
 /// <summary>
 /// 交换两个变量的值
 /// </summary>
 /// <param name="n1">形参n1</param>
 /// <param name="n2">形参n2</param>
 static private void Swap(int t1,int t2)
 {
  int temp;
  temp =t1;
  t1 =t2;
  t2 = temp;
 }

Analysis: The above code is passed by value. After exchanging the two variables, the values ​​of n1 and n2 are not changed. The fundamental reason is that the value is passed through copy. Copy form without changing the original value. The picture is as follows:

1) Define variables n1 and n2, and initialize the variables. The representation in memory is roughly as follows (int n1 = 10, n2 = 20;)

CodeDebugging

is represented in memory

2) When executing the exchange variable method

Code debugging

Represented in memory

Exchange detailed steps diagram

Reference type:

Definition: Passed by address, such as a pointer in c++. In layman's terms, just think of the address as the key to the door.

Storage method: Mainly stored in the heap.

Essence: Passed by address, shared variables, one change, all changes.

Common types: String, Object, etc.

code:c++

// Cpplus.cpp : 定义控制台应用程序的入口点。
//
#include "stdafx.h"
//主函数
int _tmain(int argc, _TCHAR* argv[])
{
 void Swap(int *x, int *y);
 int n1 = 10, n2 = 20;
 printf("交换前n1和n2的值\n");
 printf("%d,%d\n", n1, n2);
 Swap(&n1,&n2);
 printf("交换后n1和n2的值\n");
 printf("%d,%d",n1,n2);
 getchar();
 return 0;
}
//交换函数
void Swap(int *x, int *y)
{
 int temp = *x;
 *x = *y;
 *y = temp;
}

result:

2. Why are out and ref introduced

c#Introduced out and ref to solve this problem. Therefore, both out and ref are reference types.

2. Detailed explanation of out

//主函数
 static void Main(string[] args)
 {
  int n1, n2;
  Console.WriteLine(GetSum(out n1,out n2));
  Console.Read();
 }
 //out参数
 static public int GetSum(out int numberFirst,out int numberSecond)
 {
  numberFirst = 10;
  numberSecond = 3;
  return numberFirst + numberSecond;
 }

out Features:

overloaded.

//如下两个方法可以重载
public void getNumer(int num){}
public void setTime(out int num){num=10;}
//如下两个方法不能重载
public void getNumer(ref int num){num=10;}
public void setTime(out int num){num=10;}

3. Detailed explanation of ref

//主函数
 static void Main(string[] args)
 {
  int n1=1, n2=3;
  Console.WriteLine(refGetSum(ref n1,ref n2));
  Console.Read();

 } 
 //ref参数
 static public int refGetSum(ref int numberFirst, ref int numberSecond)
 {
  numberFirst = 10;
  numberSecond = 3;
  return numberFirst + numberSecond;
 }

ref特点： 

   1、方法定义和调用方法都必须显示使用ref关键字。（如上代码显然易见）

   2、ref有进有出，即可以把值传入方法体内。（如上代码，读者可以任意改变n1和n2的值）

   3、为引用类型。（直接调用而不事先定义n1和n2，编译不通过）

   4、同名函数，out不与ref同时存在，可以重载。

四、out与ref异同

主要区别，out只输出yuan'chuang，ref有进有出。

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