Detects the actual length of a string containing Chinese characters

In the actual process, we often need to check the actual length of the Chinese string,
Because of the Chinese characters, and English characters together, you are a bit more trouble to judge.
The principle is the same as in asp

ASCIIEncoding n = new ASCIIEncoding(); 
byte[] b = n.GetBytes(str); 
int l = 0; // l  Is the actual length of the string  
for (int i=0;i <= b.Length-1;i++) 
{ 
if (b[i] ==63) // Determine whether it is a Chinese character or a full-foot symbol  
{ 
l++; 
} 
l++; 
}