《C#高级编程》读书笔记（六）：字符串和正则表达式

1，创建字符串

    字符串是一个不可变的数据类型，一旦对字符串对象进行了初始化，该字符串对象就不能改变了。所以，如果用字符串频繁进行文字处理，应用程序就会遇到严重的性能问题，这时需要采用StringBuilder类。

2，对自定义结构的格式化输出

    实现IFormattable接口

struct Vector:IFormattable
    {
        public double x, y, z;


        public Vector(double x, double y, double z) : this()
        {
            this.x = x;
            this.y = y;
            this.z = z;
        }

        public Vector(Vector rhs)
        {
            x = rhs.x;
            y = rhs.y;
            z = rhs.z;
        }

        public string ToString(string format, IFormatProvider formatProvider)
        {
            if (format == null)
            {
                return ToString();
            }

            switch (format.ToUpper())
            {
                case "N":
                    return "||" + Norm().ToString() + "||";
                case "VE":
                    return $"({x:E},{y:E},{z:E})";
                default:
                    return ToString();
            }
        }

        private double Norm()
        {
            return x*x + y*y + z*z;
        }

        public override string ToString()
        {
            return "(" + x + "," + y + "," + z + ")";
        }
    }

    测试一下：

static void Main(string[] args)
        {
            var v1 = new Vector(1,4,-5);
            Console.WriteLine($"{v1,0:N}");
            Console.WriteLine($"{v1,0:VE}");
            Console.WriteLine(v1);

            Console.ReadKey();
        }

    输出：    

||42||
(1.000000E+000,4.000000E+000,-5.000000E+000)
(1,4,-5)

 3，正则表达式

const string myTest = @"This comprehensive comendium provides a broad and thorough investigation
of all aspects of programming with ASP.NET.Entirely revised and updated for the fourth release of .NET,this 
book will give you the information you need to master ASP.NET and build a dynamic,sucessful,enterprise Web 
application.";
            const string pattern = @"aS*ion";
            MatchCollection myMatches = Regex.Matches(myTest, pattern, RegexOptions.IgnoreCase|
                RegexOptions.ExplicitCapture);

            foreach (Match nextMatch in myMatches)
            {
                Console.WriteLine(nextMatch.Index);
            }