Regex not working accurately in C#

Question

I am new to C# and working with regular expressions. I have created a regex accurately and have tested online but when I use that regex in my function it always validate it as success case.

Here is my code:

 Regex regex = new Regex(@"[+]?[0-9]+");
        Match match = regex.Match(phone);
        if (match.Success)
        {
            return true;
        }
        else
        {
            return false;
        }

and I am using this number to validate : +92-322-4995562 which must be invalid according to my regex but it is returning me as match case. Please help

Hi @Tim007 , thanks for your quick response. Its working fine now. Can you please tell me why we have added ^ and +$ at the end? — Bilal Amjad, Mar 15 '16 at 06:31
**`\+?\d+`** can match `+92` or `322` or `4995562` with global/all matches. **`^\+?\d+`** only match `+92` because `^` assert position at start of a line. **`\+?\d+$`** only match `4995562` because `$` assert position at end of a line. **`^\+?\d+$`** not match `+92-322-4995562` but match entire `+923224995562` — Tim007, Mar 15 '16 at 06:42

score 3 · Answer 1 · answered Mar 15 '16 at 06:29

No, it isn't wrong because you're not anchoring the pattern.

This allows the regex engine to find a position inside the input where the pattern matches, and not be forced to check if the entire input matches.

Specifically, this pattern:

[+]?[0-9]+

Matches this part:

+92-322-4995562
^^^

To ensure it checks against the whole input you must "anchor" it by specifying that the start of the pattern has to coincide with the start of the input, and that the end of the pattern has to coincide with the end of the input.

You do this with a pattern like this:

^....$

The ^ character anchors to the start of the input and $ to the end of the input.

So your final pattern should look like this:

^[+]?[0-9]+$

score 1 · Accepted Answer · answered Mar 15 '16 at 06:31

1

try this
^[+]?[0-9]+$ or ^\+?\d+$

Explanation:
^ assert position at start of the string
\+ matches the character +
\d match a digit [0-9]
$ assert position at end of the string

answered Mar 15 '16 at 06:31

Tim007

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What matches the `-`? – adrianm Mar 15 '16 at 06:51
`-` must be invalid according to @Bilal Amjad regex – Tim007 Mar 15 '16 at 06:52
`^\+?[\d-]+$` this one will allow `-` – Tim007 Mar 15 '16 at 06:54
Sorry, didn't read the question properly – adrianm Mar 15 '16 at 06:54

Regex not working accurately in C#

2 Answers2