C# 数据类型

Char Array

Char Array储存string data。有两个方法建立StringBuilder和Character array

【Character array】

用来存储character data，比如字母和数字

好处：array element被储存在内存中的一块，避免了存储于分开的对象所带来的内存消耗。Char是基本的变量类型，她不是存储reference而是存储在内存本身。

建立char array：

using System;

class Program
{
    static void Main()
    {
    char[] array1 = { 's', 'a', 'm' };
    char[] array2 = new char[] { 's', 'a', 'm' };　　　　char[] array3 = new char[3];　　　　//可以使用这个方法，后面用for循环添加每一个character
    array3[0] = 's';
    array3[1] = 'a';
    array3[2] = 'm';
    // Write total length:
    Console.WriteLine(array1.Length + array2.Length + array3.Length);
    }
}

Output
9

【StringBuilder】

Example using char array: faster [C#]

class Program
{
    static void Main()
    {
    // Use a new char array.
    char[] buffer = new char[100];    
    for (int i = 0; i < 100; i++)
    {
        buffer[i] = 'a';
    }
    string result = new string(buffer);
    }
}

The array is instantiated with the new char syntax, and this allocates 100 2-byte chars. 
We assign each index to the char we want to append. This example uses the new string constructor.

Example using StringBuilder: slower [C#]

using System.Text;

class Program
{
    static void Main()
    {
    // Declare new StringBuilder and append to it 100 times.
    StringBuilder builder = new StringBuilder(100);
    for (int i = 0; i < 100; i++)
    {
        builder.Append('a');
    }
    string result = builder.ToString();
    }
}

The biggest advantage the StringBuilder method has is that you could keep appending items to the buffer after the 100th char.

总结：

1：Char Array比StringBuilder要来的快，因为其没有预制的很多方法。

2：StringBuilder可以Append更多的chars。StringBuilder可以使用很多预制的方法，在多数情况下使用起来很方便，但是对于简单的case，还是CharArray来的快。

3：当事先知道有多少character需要储存，我们使用Char Array。

String

【string.split】

分谁：

分一个特定string中的 ' '， \r ，\n ，',' ，按非字母元素分等等
分***.txt
Seprate words
分文件路径： @"C:\Users\Sam\Documents\Perls\Main"

分法：（2个以上的char和string分要先做一个new，实际上是按sting[]分）

char分：　　‘a’， ‘ ’， ‘\r’
char[]分： char[] delimiters = new char[] { '\r', '\n' };
string[]分：

　const string dir = @"C:\Users\hb92540\AAppData\LocalAA\Temporary Projects\ConsoleAApplication1";
  string[] seprator = new string[] {"AA","Te" };

Regex.split分

string value = "cat\r\ndog\r\nanimal\r\nperson";
    //
    // Split the string on line breaks.
    // ... The return value from Split is a string[] array.
    //
    string[] lines = Regex.Split(value, "\r\n");

附加选项：

StringSplitOptions.RemoveEmptyEntries
StringSplitOptions.None

按空格分

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string s = "there is a cat";
            string[] words = s.Split(' ');
            StringBuilder sb = new StringBuilder();
            foreach (var item in words)
            {
                Console.WriteLine(item as string);
                sb.Append(item);
            }
            Console.WriteLine(sb);
            Console.ReadLine();
        }
    }
}

Regex.Split:

using System; 
using System.Text.RegularExpressions;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            string value = "cat\r\ndog\r\nanimal\r\nperson";
            string[] lines = Regex.Split(value, "\r\n");
            foreach (var item in lines)
            {
                Console.WriteLine(item);
            }
            Console.ReadLine();
        }
    }
}

Output

cat
dog
animal
person

RemoveEmptyEntries:

using System;

class Program
{
    static void Main()
    {
    //
    // This string is also separated by Windows line breaks.
    //
    string value = "shirt\r\ndress\r\npants\r\njacket";

    //
    // Use a new char[] array of two characters (\r and \n) to break
    // lines from into separate strings. Use "RemoveEmptyEntries"
    // to make sure no empty strings get put in the string[] array.
    //
    char[] delimiters = new char[] { '\r', '\n' };
    string[] parts = value.Split(delimiters,
                     StringSplitOptions.RemoveEmptyEntries);
    for (int i = 0; i < parts.Length; i++)
    {
        Console.WriteLine(parts[i]);
    }

    //
    // Same as the previous example, but uses a new string of 2 characters.
    //
    parts = value.Split(new string[] { "\r\n" }, StringSplitOptions.None);
    for (int i = 0; i < parts.Length; i++)
    {
        Console.WriteLine(parts[i]);
    }
    }
}

Output
(Repeated two times)

shirt
dress
pants
jacket

Sperate words：

using System;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
    string[] w = SplitWords("That is a cute cat, man");
    foreach (string s in w)
    {
        Console.WriteLine(s);
    }
    Console.ReadLine();
    }

    /// <summary>
    /// Take all the words in the input string and separate them.
    /// </summary>
    static string[] SplitWords(string s)
    {
    //
    // Split on all non-word characters.
    // ... Returns an array of all the words.
    //
    return Regex.Split(s, @"\W+");
    // @      special verbatim string syntax
    // \W+    one or more non-word characters together
    }
}

Output

That
is
a
cute
cat
man

分路径：

using System;

class Program
{
    static void Main()
    {
    // The directory from Windows
    const string dir = @"C:\Users\Sam\Documents\Perls\Main";
    // Split on directory separator
    string[] parts = dir.Split('\\');　　　　//escape “\”
    foreach (string part in parts)
    {
        Console.WriteLine(part);
    }
    }
}

Output

C:
Users
Sam
Documents
Perls
Main

执行效率：

//
// Build long string.
//
_test = string.Empty;
for (int i = 0; i < 120; i++)
{
    _test += "01234567\r\n";
}
//
// Build short string.
//
_test = string.Empty;
for (int i = 0; i < 10; i++)
{
    _test += "ab\r\n";
}

Methods tested: 100000 iterations

static void Test1()
{
    string[] arr = Regex.Split(_test, "\r\n", RegexOptions.Compiled);
}

static void Test2()
{
    string[] arr = _test.Split(new char[] { '\r', '\n' },
                   StringSplitOptions.RemoveEmptyEntries);
}

static void Test3()
{
    string[] arr = _test.Split(new string[] { "\r\n" },
                   StringSplitOptions.None);

结果：少量的字char[].split更快。For somewhat longer strings or files that contain more lines, Regex is appropriate.

Benchmark of Split on long strings

[1] Regex.Split:    3470 ms
[2] char[] Split:   1255 ms [fastest]
[3] string[] Split: 1449 ms

Benchmark of Split on short strings

[1] Regex.Split:     434 ms
[2] char[] Split:     63 ms [fastest]
[3] string[] Split:   83 ms

在loop外分更好：

Slow version, before [C#]

//
// Split on multiple characters using new char[] inline.
//
string t = "string to split, ok";

for (int i = 0; i < 10000000; i++)
{
    string[] s = t.Split(new char[] { ' ', ',' });　　　　//loop内分
}

Fast version, after [C#]

//
// Split on multiple characters using new char[] already created.
//
string t = "string to split, ok";
char[] c = new char[]{ ' ', ',' }; // <-- Cache this，loop外分

for (int i = 0; i < 10000000; i++)
{
    string[] s = t.Split(c);
}

File 操作：

File.ReadAllLines：

using System;
using System.IO;

class Program
{
    static void Main()
    {
    int i = 0;
    foreach (string line in File.ReadAllLines("TextFile1.txt"))
    {
        string[] parts = line.Split(',');
        foreach (string part in parts)
        {
        Console.WriteLine("{0}:{1}",
            i,
            part);
        }
        i++; // For demo only
    }
    }
}

Output

0:Dog
0:Cat
0:Mouse
0:Fish
0:Cow
0:Horse
0:Hyena
1:Programmer
1:Wizard
1:CEO
1:Rancher
1:Clerk
1:Farmer