C# 中的值傳遞與引用傳遞

首先明確一個概念：值傳遞和引用傳遞，是指在方法中傳遞參數的方式。

既然是在方法的區別的話，那麼咱們首先首先總結幾個方法出來。

傳遞類型	參數數據類型爲值類型和引用數據類型	特色
值傳遞	Sum(int num1,int num2)	修改了形參內容，結果不會保留
	Sum(int [] num1)	修改了形參內容，結果會保留
引用傳遞	Sum(ref int num1,ref int num2)	使用 ref ，實參必需要初始化賦值；修改了形參內容，結果會保留
	Sum(out int num1,out int num2)	使用out，形參必需要賦值；修改了形參內容，結果會保留

 

示例：

定義一個計算器類：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Lesson3
{

    /// <summary>
    /// 計算器類
    /// </summary>
    public class Calc
    {
        /// <summary>
        /// 求和：參數是int——值類型
        /// </summary>
        public int Sum(int num1, int num2)
        {

            int sum = 0;
            num1 = 10;
            sum = num1 + num2;

            return sum;

        }

        /// <summary>
        /// 求和：參數是數組——引用類型
        /// </summary> 
        public int SumParam(int[] nums)
        {
            nums[0] = 10;
            int sum = nums[0] + nums[1];

            return sum;
        }

        /// <summary>
        /// 求和：參數是值類型——引用傳遞
        /// </summary> 
        public int SumRef(ref int num1, ref int num2) {
            int sum = 0;
            num1 = 10;
            sum = num1 + num2;

            return sum;

        }

        /// <summary>
        /// 交換兩個數
        /// </summary>
        /// <param name="num1"></param>
        /// <param name="num2"></param>
        public void Swap(int num1,int num2) {

            int temp = 0;

            temp = num1;
            num1 = num2;
            num2 = temp;

        }


        /// <summary>
        /// 交換兩個數
        /// </summary>
        /// <param name="num1"></param>
        /// <param name="num2"></param>
        public void SwapRef(ref int num1, ref int num2)
        {

            int temp = 0;

            temp = num1;
            num1 = num2;
            num2 = temp;

        }
    }
}

 

測試類：

// 求和：值傳遞
            Calc calc = new Calc();
            int num1 = int.Parse(Console.ReadLine());
            int num2 = int.Parse(Console.ReadLine());

            // 
            int sum = calc.Sum(num1, num2);

            // 輸出和
            Console.WriteLine(num1 + "+" + num2 + "=" + sum);


            // 求和：參數是數組——值傳遞
            Calc calc1 = new Calc();

            int[] nums = { 1, 2 };


            int sum1 = calc1.SumParam(nums);
            // 輸出和
            Console.WriteLine(nums[0] + "+" + nums[1] + "=" + sum1);



            // 求和：參數是ref關鍵字——引用傳遞
            Calc calc2 = new Calc();
            int refNum1 = 1;
            int refNum2 = 2;

            int refSum = calc2.SumRef(ref refNum1, ref refNum2);

            // 輸出和
            Console.WriteLine(refNum1 + "+" + refNum2 + "=" + refSum);




            // 交換兩個數

            //Calc calc = new Calc();

            //int num1 = 8;

            //int num2 = 10;
            //Console.WriteLine("值傳遞：交換前的數是" + num1 + "," + num2);

            //// 交換
            //calc.Swap(num1, num2);
            //Console.WriteLine("值傳遞：交換後的數是" + num1 + "," + num2);




            //int num1Ref = 8;

            //int num2Ref = 10;
            //Console.WriteLine("引用傳遞：交換前的數是" + num1Ref + "," + num2Ref);

            //// 交換
            //calc.SwapRef(ref num1Ref, ref  num2Ref);
            //Console.WriteLine("引用傳遞：交換後的數是" + num1Ref + "," + num2Ref);