Question

can someone write a regex in C# for me to verify the following emails ?

[e-mail];[e-mail];[e-mail];[e-mail];

every email addresses are seperated with “;”, and I have wrote the following regex:

^(([0-9a-zA-Z]([-\.\w]*[0-9a-zA-Z])*@([0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9});)*$

when use this regex to match a string, it might cause a dead loop, why ?

Thanks in advance!

Answer 1

Your regular expression suffers from catastrophic backtracking. I added atomic groups to your regular expression to create this:

^(([0-9a-zA-Z](?>(?>[-\.\w]*[0-9a-zA-Z])*@)(?>(?>[0-9a-zA-Z][-\w]*[0-9a-zA-Z]\.)+[a-zA-Z]{2,9}));)*$