Regex validates years bisexto and not bisextos in format:
const std::regex pattern(R"(^(?:(?:(0?[1-9]|1\d|2[0-8])([-/.])(0?[1-9]|1[0-2]|[Jj](?:an|u[nl])|[Mm]a[ry]|[Aa](?:pr|ug)|[Ss]ep|[Oo]ct|[Nn]ov|[Dd]ec|[Ff]eb)|(29|30)([-/.])(0?[13-9]|1[0-2]|[Jj](?:an|u[nl])|[Mm]a[ry]|[Aa](?:pr|ug)|[Ss]ep|[Oo]ct|[Nn]ov|[Dd]ec)|(31)([-/.])(0?[13578]|1[02]|[Jj]an|[Mm]a[ry]|[Jj]ul|[Aa]ug|[Oo]ct|[Dd]ec))(?:\2|\5|\8)(0{2,3}[1-9]|0{1,2}[1-9]\d|0?[1-9]\d{2}|[1-9]\d{3})|(29)([-/.])(0?2|[Ff]eb)\12(\d{1,2}(?:0[48]|[2468][048]|[13579][26])|(?:0?[48]|[13579][26]|[2468][048])00))$)");

this regex above validates the formats through backreferences.

dd-mm-yyyy ou dd-str-yyyy ou dd-Str-yyyy
dd/mm/yyyy ou dd/str/yyyy ou dd/Str/yyyy
dd.mm.yyyy ou dd.str.yyyy ou dd.Str.yyyy



Regex validates years bisexto and not bisextos in format:
const std::regex pattern(R"(^(?:\d{4}([-/.])(?:(?:(?:(?:0?[13578]|1[02]|[Jj](?:an|ul)|[Mm]a[ry]|[Aa]ug|[Oo]ct|[Dd]ec)([-/.])(?:0?[1-9]|[1-2][0-9]|3[01]))|(?:(?:0?[469]|11|[Aa]pr|[Jj]un|[Ss]ep|[Nn]ov)([-/.])(?:0?[1-9]|[1-2][0-9]|30))|(?:(0?2|[Ff]eb)([-/.])(?:0?[1-9]|1[0-9]|2[0-8]))))|(?:(?:\d{2}(?:0[48]|[2468][048]|[13579][26]))|(?:(?:[02468][048])|[13579][26])00)([-/.])(0?2|[Ff]eb)([-/.])29)$)");

this regex above had to validate the formats through backreferences.

but it is validating in the following formats
yyyy-mm/dd ou yyyy-str/dd ou yyyy-Str/dd
yyyy/mm.dd ou yyyy/str.dd ou yyyy/Str.dd
yyyy.mm-dd ou yyyy.str-dd ou yyyy.Str-dd


when it had to validate only in the following formats
yyyy-mm-dd ou yyyy-str-dd ou yyyy-Str-dd
yyyy/mm/dd ou yyyy/str/dd ou yyyy/Str/dd
yyyy.mm.dd ou yyyy.str.dd ou yyyy.Str.dd

how do I do it validate only with some of the tabs?

On Wednesday, 28 February 2018 at 01:06:30 UTC, dark777 wrote:
> Regex validates years bisexto and not bisextos in format:
> const std::regex pattern(R"(^(?:(?:(0?[1-9]|1\d|2[0-8])([-/.])(0?[1-9]|1[0-2]|[Jj](?:an|u[nl])|[Mm]a[ry]|[Aa](?:pr|ug)|[Ss]ep|[Oo]ct|[Nn]ov|[Dd]ec|[Ff]eb)|(29|30)([-/.])(0?[13-9]|1[0-2]|[Jj](?:an|u[nl])|[Mm]a[ry]|[Aa](?:pr|ug)|[Ss]ep|[Oo]ct|[Nn]ov|[Dd]ec)|(31)([-/.])(0?[13578]|1[02]|[Jj]an|[Mm]a[ry]|[Jj]ul|[Aa]ug|[Oo]ct|[Dd]ec))(?:\2|\5|\8)(0{2,3}[1-9]|0{1,2}[1-9]\d|0?[1-9]\d{2}|[1-9]\d{3})|(29)([-/.])(0?2|[Ff]eb)\12(\d{1,2}(?:0[48]|[2468][048]|[13579][26])|(?:0?[48]|[13579][26]|[2468][048])00))$)");
>
> this regex above validates the formats through backreferences.
>

what is this evil dark magic?

On Wednesday, 28 February 2018 at 05:09:03 UTC, psychoticRabbit wrote:
> On Wednesday, 28 February 2018 at 01:06:30 UTC, dark777 wrote:
>> Regex validates years bisexto and not bisextos in format:
>> const std::regex pattern(R"(^(?:(?:(0?[1-9]|1\d|2[0-8])([-/.])(0?[1-9]|1[0-2]|[Jj](?:an|u[nl])|[Mm]a[ry]|[Aa](?:pr|ug)|[Ss]ep|[Oo]ct|[Nn]ov|[Dd]ec|[Ff]eb)|(29|30)([-/.])(0?[13-9]|1[0-2]|[Jj](?:an|u[nl])|[Mm]a[ry]|[Aa](?:pr|ug)|[Ss]ep|[Oo]ct|[Nn]ov|[Dd]ec)|(31)([-/.])(0?[13578]|1[02]|[Jj]an|[Mm]a[ry]|[Jj]ul|[Aa]ug|[Oo]ct|[Dd]ec))(?:\2|\5|\8)(0{2,3}[1-9]|0{1,2}[1-9]\d|0?[1-9]\d{2}|[1-9]\d{3})|(29)([-/.])(0?2|[Ff]eb)\12(\d{1,2}(?:0[48]|[2468][048]|[13579][26])|(?:0?[48]|[13579][26]|[2468][048])00))$)");
>>
>> this regex above validates the formats through backreferences.
>>
>
> what is this evil dark magic?

Something that is horribly slow and might be incorrect, there are very few reasons to write large regexes like that and they usually boil down to “it only accepts regex” otherwise parser combinators are much better fit.