[英]How do I make Regex capture only named groups
根據Regex
文檔,使用RegexOptions.ExplicitCapture
可使Regex僅匹配命名的組,例如(?<groupName>...)
; 但是在實際操作中卻有所不同。
考慮以下幾行代碼:
static void Main(string[] args) {
Regex r = new Regex(
@"(?<code>^(?<l1>[\d]{2})/(?<l2>[\d]{3})/(?<l3>[\d]{2})$|^(?<l1>[\d]{2})/(?<l2>[\d]{3})$|(?<l1>^[\d]{2}$))"
, RegexOptions.ExplicitCapture
);
var x = r.Match("32/123/03");
r.GetGroupNames().ToList().ForEach(gn => {
Console.WriteLine("GroupName:{0,5} --> Value: {1}", gn, x.Groups[gn].Success ? x.Groups[gn].Value : "");
});
}
運行此代碼段時,您會看到結果包含一個名為0的組,而我的正則表達式中沒有一個名為0的組!
GroupName: 0 --> Value: 32/123/03
GroupName: code --> Value: 32/123/03
GroupName: l1 --> Value: 32
GroupName: l2 --> Value: 123
GroupName: l3 --> Value: 03
Press any key to continue . . .
有人可以向我解釋這種行為嗎?
您總是有第0組:這就是整個比賽。 基於定義組的開頭括號的序號位置,編號的組相對於1。 您的正則表達式(為清晰起見而設置):
(?<code>
^
(?<l1> [\d]{2} )
/
(?<l2> [\d]{3} )
/
(?<l3> [\d]{2} )
$
|
^
(?<l1>[\d]{2})
/
(?<l2>[\d]{3})
$
|
(?<l1> ^[\d]{2} $ )
)
您的表達式將回退,因此您可以考慮簡化正則表達式。 這可能更清晰,更有效:
static Regex rxCode = new Regex(@"
^ # match start-of-line, followed by
(?<code> # a mandatory group ('code'), consisting of
(?<g1> \d\d ) # - 2 decimal digits ('g1'), followed by
( # - an optional group, consisting of
/ # - a literal '/', followed by
(?<g2> \d\d\d ) # - 3 decimal digits ('g2'), followed by
( # - an optional group, consisting of
/ # - a literal '/', followed by
(?<g3> \d\d ) # - 2 decimal digits ('g3')
)? # - END: optional group
)? # - END: optional group
) # - END: named group ('code'), followed by
$ # - end-of-line
" , RegexOptions.IgnorePatternWhitespace|RegexOptions.ExplicitCapture );
一旦有了,就可以這樣:
string[] texts = { "12" , "12/345" , "12/345/67" , } ;
foreach ( string text in texts )
{
Match m = rxCode.Match( text ) ;
Console.WriteLine("{0}: match was {1}" , text , m.Success ? "successful" : "NOT successful" ) ;
if ( m.Success )
{
Console.WriteLine( " code: {0}" , m.Groups["code"].Value ) ;
Console.WriteLine( " g1: {0}" , m.Groups["g1"].Value ) ;
Console.WriteLine( " g2: {0}" , m.Groups["g2"].Value ) ;
Console.WriteLine( " g3: {0}" , m.Groups["g3"].Value ) ;
}
}
產生預期
12: match was successful
code: 12
g1: 12
g2:
g3:
12/345: match was successful
code: 12/345
g1: 12
g2: 345
g3:
12/345/67: match was successful
code: 12/345/67
g1: 12
g2: 345
g3: 67
命名組
^(?<l1>[\d]{2})/(?<l2>[\d]{3})/(?<l3>[\d]{2})$|^(?<l1>[\d]{2})/(?<l2>[\d]{3})$|(?<l1>^[\d]{2}$)
試試這個(我從您的正則表達式中刪除第一組)- 參見演示
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