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Is my Regex Syntax correct in C#

Posted on 2011-03-25
Medium Priority
Last Modified: 2012-05-11
Most irrrefutable guru's,

As a C# newbie I am needing a reality check  for correct syntax of a Regex statement where I am checking for the existance of a string within a string.   I am basically looking for a replacement for the Mid$ function in VB.Net

Please correct and enlighten me if I am wrong.

Thank You

using System;
using System.Text.RegularExpressions;

public string getBrowser()
       string functionReturnValue = null 
       string searchforthis="Netscape";
        Match q = Regex.Match(user_agent,searchforthis);
        if (q.Success)        {
        functionReturnValue = "ns4";

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Question by:tcalbaz
  • 4
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LVL 23

Expert Comment

by:Jens Fiederer
ID: 35218280
To look for a simple string, Regex is a bit overpowered - just IndexOf should do for you.

Author Comment

ID: 35218852

At heart, I would have to agree with you.

However, I did try IndexOf first and it seemed to me to be obtuse about searching for strings with more then one char character and in the end it got rather complex.  

I found the Regex method a little more concise.  

My question: is this correct syntax?  

The compiler passed it but I don't know if is the correct approach.  I want it give me the starting integer ordinal position of the substring within the string.

LVL 23

Accepted Solution

Jens Fiederer earned 500 total points
ID: 35218918
That is the correct syntax, assuming user_agent is the string within which you wish to search.

The starting position of the substring you found will be at q.Index (0-based, add one if you want your ordinals to start with 1).

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LVL 75

Assisted Solution

by:käµfm³d 👽
käµfm³d   👽 earned 500 total points
ID: 35219740
>>  However, I did try IndexOf first and it seemed to me to be obtuse

Interesting. I've always found IndexOf() to be pretty straight-forward. The main benefit of regex over a simple IndexOf() is that you can make the search case-insenstive. In this way, you could pass "findme" as the string to find and locate any of the following:


You can also use the Contains() method (though it suffers from the same negative as IndexOf()):
Dim source As String = "Luke, come to the dark side!"
Dim found As Boolean = source.Contains("dark")

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LVL 23

Expert Comment

by:Jens Fiederer
ID: 35219775
Contains would give him the same result as q.success, but not " the starting integer ordinal position of the substring within the string".

And, yes, any problems in IndexOf (which gives you just that, or -1 if not found) are likely to some confusion that resulted during use rather than any deficiencies in the method itself.

As kaufmed points out, the main reason for using regex is case-insensitivity (or more complex patterns, like strings of digits of unknown length).
LVL 75

Expert Comment

by:käµfm³d 👽
ID: 35220053
>>  " the starting integer ordinal position of the substring within the string".

I missed that in the author's last post, but I agree, it would not give starting index--it would give "true" or "false" as demonstrated by the type of the variable storing the result. There is a discrepancy about what the desired result is--the OP demonstrates one type of return value; the last post indicates something different.

Expert Comment

ID: 35221490
you can use

If Regex.IsMatch(strlText, "^error") Then

end if

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Author Closing Comment

ID: 35224042
This was an interesting discussion and I found  both your answers very helpful.  

I never knew about the 'contains' keyword.  Thank you so much!

LVL 75

Expert Comment

by:käµfm³d 👽
ID: 35228464
Glad to be of service  = )
LVL 23

Expert Comment

by:Jens Fiederer
ID: 35228780
How civilized, it's been fun

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