c# - regex works in online regex tester but not in .NET -

the following demo works fine online not when attempt run in c#/.net

 var regex = new regularexpressionattribute(@"@(?!.*?\.\.)[^@]+$");  assert.istrue(regex.isvalid("bob@bob.com")); 

here link post explain regex , trying

the regularexpressionattribute requires full match of string.

in case, matching starting @ @ character, start somewhere in between of string. not enough regularexpressionattribute. can think of adding implicit ^ @ start expression (and implicit $ @ end too, can drop well).

so fix this, need make sure has match @ start to, e.g. .*?:

new regularexpressionattribute(@".*?@(?!.*?\.\.)[^@]+"); 

and works. don’t need other regular expression flags.

---

unfortunately, behavior of regularexpressionattribute mentioned in documentation. can verify in reference source however:

// looking exact match, not search hit. matches // regularexpressionvalidator control return (m.success && m.index == 0 && m.length == stringvalue.length); 

so it’s technically not added ^ , $ after finding match, start , end index required match string’s start , end index (which same thing).

and if think it, behavior makes lot of sense validation. after all, want make sure string matches full-specified format, , not check if substring valid.