C# 取字符串中间文本 取字符串左边 取字符串右边

　　好像是第二种效率高一点，取str字符串中123左边的所有字符：第一种Between(str,"","123")，而第二种是Between(str,null,"123")。

public static string Between(string str, string strLeft, string strRight) //取文本中间
{
    if (str == null || str.Length == 0) return "";
    if (strLeft != "")
    {
        int indexLeft = str.IndexOf(strLeft);//左边字符串位置
        if (indexLeft < 0) return "";
        indexLeft = indexLeft + strLeft.Length;//左边字符串长度
        if (strRight != "")
        {
            int indexRight = str.IndexOf(strRight, indexLeft);//右边字符串位置
            if (indexRight < 0) return "";
            return str.Substring(indexLeft, indexRight - indexLeft);//indexRight - indexLeft是取中间字符串长度
                }
        else return str.Substring(indexLeft, str.Length - indexLeft);//取字符串右边
    }
    else//取字符串左边
    {
        int indexRight = str.IndexOf(strRight);
        if (indexRight <= 0) return "";
        else return str.Substring(0, indexRight);
    }
}

　　

public static string Between2(string str, string strLeft, string strRight) //取文本中间
{
    if (str == null || str.Length == 0) return "";
    if (strLeft != null)
    {
        int indexLeft = str.IndexOf(strLeft);//左边字符串位置
        if (indexLeft < 0) return "";
        indexLeft = indexLeft + strLeft.Length;//左边字符串长度
        if (strRight != null)
        {
            int indexRight = str.IndexOf(strRight, indexLeft);//右边字符串位置
            if (indexRight < 0) return "";
            return str.Substring(indexLeft, indexRight - indexLeft);//indexRight - indexLeft是取中间字符串长度
                }
        else return str.Substring(indexLeft, str.Length - indexLeft);//取字符串右边
    }
    else//取字符串左边
    {
        if (strRight == null) return "";
        int indexRight = str.IndexOf(strRight);
        if (indexRight <= 0) return "";
        else return str.Substring(0, indexRight);
    }
}