csharp中byte於string轉換

1 string和byte[]的轉換 (C#)
2 Encoding.ASCII與Encoding.Unicode

1 string和byte[]的轉換 (C#)

string類型轉成byte[]：

byte[] byteArray = System.Text.Encoding.Default.GetBytes(str);

反過來，byte[]轉成string：

string str = System.Text.Encoding.Default.GetString(byteArray);

其它編碼方式的，如System.Text.UTF8Encoding，System.Text.UnicodeEncoding等；例如： string類型轉成ASCII byte[]：（"01" 轉成 byte[] = new byte[]{ 0x30, 0x31}）

byte[] byteArray = System.Text.Encoding.ASCII.GetBytes(str);

ASCII byte[] 轉成string：（byte[] = new byte[]{ 0x30, 0x31} 轉成 "01"）

string str = System.Text.Encoding.ASCII.GetString ( byteArray );

有時候還有這樣一些需求：

byte[] 轉成原16進制格式的string，例如0xae00cf, 轉換成 "ae00cf"；new byte[]{ 0x30, 0x31}轉成"3031":

public static string ToHexString ( byte[] bytes ) // 0xae00cf => "AE00CF "
{
    string hexString = string.Empty;
    if ( bytes != null )
    {
        StringBuilder strB = new StringBuilder ();

        for ( int i = 0; i < bytes.Length; i++ )
        {
            strB.Append ( bytes[i].ToString ( "X2" ) );
        }
        hexString = strB.ToString ();
    }
    return hexString;
}

反過來，16進制格式的string 轉成byte[]，例如, "ae00cf"轉換成0xae00cf，長度縮減一半；"3031" 轉成new byte[]{ 0x30, 0x31}:

public static byte[] GetBytes(string hexString, out int discarded)
{
    discarded = 0;
    string newString = "";
    char c;
    // remove all none A-F, 0-9, characters
    for (int i=0; i<hexString.Length; i++)
    {
        c = hexString[i];
        if (IsHexDigit(c))
            newString += c;
        else
            discarded++;
    }
    // if odd number of characters, discard last character
    if (newString.Length % 2 != 0)
    {
        discarded++;
        newString = newString.Substring(0, newString.Length-1);
    }

    int byteLength = newString.Length / 2;
    byte[] bytes = new byte[byteLength];
    string hex;
    int j = 0;
    for (int i=0; i<bytes.Length; i++)
    {
        hex = new String(new Char[] {newString[j], newString[j+1]});
        bytes[i] = HexToByte(hex);
        j = j+2;
    }
    return bytes;
}

2 Encoding.ASCII與Encoding.Unicode

用Encoding.Unicode.GetBytes()轉換字節數組是兩個字節表示一個字符，比如：

byte[] bytes = Encoding.Unicode.GetBytes("ab");
// bytes = [0x61, 0x00, 0x62, 0x00];
// 用bytes轉換成string，也要用Encoding.Unicode
string str = Encoding.Unicode.GetString(bytes);
// str = "ab";

如果用Encoding.Unicode.GetBytes()轉換的字節數組，用Encoding.Acsii轉換成字符串，轉換結果是錯誤的，必須Encoding.Convert進行編碼轉換。

byte[] bytes = Encoding.Unicode.GetBytes("ab");
// bytes = [0x61, 0x00, 0x62, 0x00];
// 用bytes轉換成string，用Encoding.ASCII
string str = Encoding.ASCII.GetString(bytes);  
// str = "a\0b\0"
// 編碼轉換
byte[] asciiBytes = Encoding.Convert(Encoding.Unicode, Encoding.ASCII, bytes);  
// asciiBytes = [0x61, 0x62];
// 用asciiBytes轉換成string，用Encoding.ASCII
string str1 = Encoding.ASCII.GetString(bytes);    
// str1 = "ab"