c# - Regex option "Multiline" -

i have regex match date format comma.

yyyy/mm/dd or yyyy/mm

for example:

2016/09/02,2016/08,2016/09/30

my code:

string data="21535300/11/11\n"; regex reg = new regex(@"^(20\d{2}/(0[1-9]|1[012])(/(0[1-9]|[12]\d|30|31))?,?)*$",                        regexoptions.multiline);  if (!reg.ismatch(data))     "error".dump(); else     "true".dump(); 

i use option multiline. if string data have "\n". character match regex.

for example:

string data="test\n" string data="2100/1/1" 

i find option definition in msdn. says:

it changes interpretation of ^ , $ language elements match beginning , end of line, instead of beginning , end of input string.

i didn't understand why problem has happened. can explan it? thanks.

your regex can match empty line once add newline @ end of string. "test\n" contains 2 lines, , second 1 gets matched.

see regex pattern in free-spacing mode:

^                 # matches start of line  (                # start of group 1    20\d{2}/    (0[1-9]|1[012])    (/      (0[1-9]|[12]\d|30|31)    )?,?  )*                # end of group 1 - * quantifier makes match 0+ times $                  # end of line 

if not want match empty line, replace last )* )+.

an alternative use more unrolled pattern like

^20\d{2}/(0[1-9]|1[012])(/(0[1-9]|[12]\d|3[01]))?(,20\d{2}/(0[1-9]|1[012])(/(0[1-9]|[12]\d|3[01]))?)*$ 

see regex demo. inside code, advisable use block , build pattern dynamically:

string date = @"20\d{2}/(0[1-9]|1[012])(/(0[1-9]|[12]\d|3[01]))?"; regex reg = new regex(string.format("^{0}(,{0})*$", date), regexoptions.multiline); 

as can see, first block (after start of line ^ anchor) obligatory here, , empty line never matched.