C#中获取字符串字节长度的方法

//...

//读取字符串的方法
string value = null;
if (br != null)
{
value = br.ReadString();
}
ASCIIEncoding strData = new ASCIIEncoding();
byte[] strBytes = strData.GetBytes(value);

for (int i = 0; i <= strBytes.Length - 1; i++)
{
byte s = Convert.ToByte(strBytes[i] & 0xFF);
if (s != 0) //GBK编码，中文不为0
m_nOffest++;
m_nOffest++;
}
m_nOffest += 4;//加上描述长度的4字节

//貌似下面方法肯定没问题

long tmpLen = br.BaseStream.Position;
value = br.ReadString();
tmpLen = br.BaseStream.Position - tmpLen;
m_nOffest += (int)tmpLen;