I need to validate a user input based on condition. i wrote a regular expression to do so, but it's failing not sure why. Can somebody point where i am making mistake?
Regex AccuracyCodeHexRegex = new Regex(@"^[PTQA]((0|8)[01234567]){2}$");
This is what i am trying to validate(If the string is a subset of these strings then it is valid):
Phh, Thh, Qhh, Ahh where 'h' is a hex digit in the set {00, 80, 01, 81, 02, 82, 03, 83, 04, 84, 05, 85, 06, 86, 07, 87}
Ex: P00 is valid P20 is not valid
I would write :
^[PTQA]((0|8)[0-7])$
you don't seem to need the {2}
which validates strings like P0707
Your Regex ^[PTQA](?:(?:0|8)[01234567]){2}$
Applies to the following :
P8001
P8002
P0281
P8005
and so on, because you are repeating the number matches by {2}
To validate something like P81 / P05, you need to change that to {1}
you can simplify your regex to ^[PTQA](?:(?:0|8)[0-7])$
which will do the trick for you
if you need speed regex aren't terribly fast and usually simple lookups on static values can be implemented with a switch-case. They aren't that nice when it comes to maintainability but if the values are fairly stable and only used in this one place that shouldn't be too much of a concern. If it is you can use a HashSet of all the valid values.
Using a HashSet:
var leading = new[]{'P','T','Q','A'};
var firstDigit = new []{'0','8'};
var lastDigit = new []{'0','1','2','3','4','5','6','7'};
var set = new HashSet<string>(from l in leading
from f in firstDigit
from lst in lastDigit
select l + f + lst);
public bool IsOk(string value){
return set.Contains(value);
}
or using switch-case:
public bool IsOk(string value){
if(value.length != 3) return false;
switch(value[0]){
case 'P':
case 'T':
case 'Q':
case 'A':
switch(value[1]){
case '0':
case '8':
switch(value[2]){
case '0':
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
return true;
}
}
}
return false;
}
If you sort the possible hex digits in a list you could build the regex automatically like so
var hexs = new List {"00", "80", "01", "81", "02"};
var regex = string.Format("^[PTQA]({0})", string.Join("|", hexs));
var accuracyCodeHexRegex = new Regex(regex);
If the possible values are known, why don't you compare to an array of this known possibles values?
void Foo(){
var valueToTest1 = "P07";
var valueToText2 = "Z54";
TestValue(valueToTest1);
TestValue(valueToTest1);
}
bool TestValue(string stringToTest)
{
var hexValues = new string[] { "00", "80", "01", "81", "02", "82", "03", "83", "04", "84", "05", "85", "06", "86", "07", "87"};
var leftValues = new char[] { 'P', 'Q', 'H' };
var left = stringToTest[0];
var right = strintToTest.SubString(1,2);
return leftValues.Contains(left) && hexValues.Contains(right);
}
This is a lot simpler than using a regex and I believe far more performant
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