Fastest way to check if string contains only digits

Question

I know a few ways how to check this. regex,int.parse,tryparse,looping.

can anyone tell me what is the fastest way to check?

the nee

Answer 1

Another approach!

string str = "12345";
bool containsOnlyDigits = true;
try { Convert.ToInt32(str); }
catch { containsOnlyDigits = false; }