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Is my Regex Syntax correct in C#

Posted on 2011-03-25
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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
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Expert Comment

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

by:tcalbaz
ID: 35218852
jensfiederer,

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.

regards,
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Accepted Solution

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Jens Fiederer earned 125 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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Assisted Solution

by:käµfm³d 👽
käµfm³d   👽 earned 125 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:

findme
FINDME
FiNdMe

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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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).
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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.
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by:coolcurrent4u
ID: 35221490
you can use


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

.....
end if

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Author Closing Comment

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

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

Ted
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by:käµfm³d 👽
ID: 35228464
Glad to be of service  = )
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by:Jens Fiederer
ID: 35228780
How civilized, it's been fun
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