用Split劈开一个字符串

private string splitstr(string str)
{
string str = "xxxxxx[12345]";
string[] a = str.Split('[');
//a[0] = "xxxxxx";
//a[1] = "12345]";
if(a.Length >1)
{
string[] b = a[1].Split(']');
return b[0];
}
else
{
string[] b = {""};
return b[0];
}
}