Any custom function to extract parameters from strings?

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1.50/5 (2 votes)

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I once came across a function in VB6 that received 3 parameters "Parameter","Match" and "Delimiter" that could extract information from a given string as follows:
SiteAddress=XXXX;UID=XXXX;PWD=XXXX

In which SiteAddress, for example, is a parameter, ";" is the delimiter and "=" is the match. I wonder if anyone can help me have one written in C#.

Posted 27-Sep-14 3:28am

Medise

Updated 27-Sep-14 4:13am

Sergey Alexandrovich Kryukov

v2

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[no name] 27-Sep-14 9:48am

String.Split

Richard MacCutchan 27-Sep-14 9:59am

That's a solution, and a good one.

Sergey Alexandrovich Kryukov 27-Sep-14 10:11am

Of course. Regex solution will be much uglier.
—SA

Sergey Alexandrovich Kryukov 27-Sep-14 10:12am

What have you tried so far?
—SA

PIEBALDconsult 27-Sep-14 10:28am

Remember that today's passwords should contain "special characters" and so may include your match and delimiter characters so you need to support that.
String.Split won't honor quotes; I'd use a Regular Expression.

BillWoodruff 27-Sep-14 10:57am

That's a damn good point ! If we knew more about the exact format of the string, and any possible variations, the OP was trying to parse, we could be more specific about what is required. But, whether using code, or RegEx, I think there must be some minimum "organizing principle" to locate the delimiters: otherwise it's bit-salad buffet :)

BillWoodruff 27-Sep-14 10:54am

If you are here because you are learning C# programming, why not take the clue about String.Split in the comment above, and start working/coding with that method, then come back here with specific questions and code examples ?

If we just write the answer for you, you will learn less.

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Sergey Alexandrovich Kryukov · Answer 1 · 2014-09-27T04:11:00

Solution 1

Why "custom functions"? Try something like

C#

using StringDictionary = System.Collections.Specialized.StringDictionary;

// ...

static StringDictionary ParseKeyValues(string source, char parameterDelimiter, char keyValueDelimiter) {
    StringDictionary result = new StringDictionary();
    string[] parameters =
        source.Split(
            new char[] { parameterDelimiter },
            System.StringSplitOptions.RemoveEmptyEntries);
    foreach (string parameter in parameters) {
        string[] pair = parameter.Split(new char[] { keyValueDelimiter });
        string key = pair[0]; // always exist due to previous split options
        string value = null;
        if (pair.Length > 1)
            value = pair[1];
        result.Add(key, value); // may throw exception
    } //loop
    return result;
} //ParseKeyValues

A Regular Expression solution exist but will be uglier, as the number of parameters is unknown.

—SA

Posted 27-Sep-14 4:11am

Sergey Alexandrovich Kryukov

Updated 27-Sep-14 19:34pm

v2

Comments

BillWoodruff 27-Sep-14 10:52am

Error in your code: should be: result.Add(key, value); ?

fyi: As of .NET 1.1, in the System.Collections.Specialized Namespace, there is a Dictionary named 'StringDictionary:

http://msdn.microsoft.com/en-us/library/System.Collections.Specialized.StringDictionary(v=vs.85).aspx

It's "hard-coded" to support only Type 'String keys, and values.

I am not competent in "RegEx," but I do wonder, given the "back-tracking" capabilities of Regular Expressions, what you mean by implying it would be difficult to handle an unknown number of parameters: what exactly do you reference when you write "parameters:" do you mean each delimiter parameter could have more than one character in the char[] ?

cheers, Bill

Sergey Alexandrovich Kryukov 28-Sep-14 1:29am

Sure, this is a bug; thank you very much, fixed.
By a "parameter", I mean each of key/value pairs. It's quite possible to do with Regex, but I see no point. OP shows 3 such parameters, but who knows how many are their. Regex for exactly 3 parameters would be the easiest, but for unknown number of then, one would need to traverse all the recognized groups anyway, which would make the solution longer then this one, and much less readable.
—SA

BillWoodruff 28-Sep-14 2:54am

Your (corrected) answer gets my 5; it's a good "generalized" lesson on string parsing, and storing the result of parsing in a Dictionary for fast look-up. I don't see why this answer should ever have gotten a #2 vote.

In this particular case, if the user only needs to parse one time for a very limited number of key-value pairs, a Dictionary may be a bit of over-kill. Of course, as usual, we don't know ... and will probably never know ... what the user needs :)

The good thing about examples like this is: if the user understands the code, they can then write other "tailored" versions, possibly more simple, for a wide variety of cases.

The fans of RegEx (I'm not one in most cases) would, I think, argue about the performance of using 'grouping to parse a variable length input into a collection of "chunks" vs. the "hand-coded" approach, particularly if the RegEx is compiled, but such a comparison is beyond my abilities.

Sergey Alexandrovich Kryukov 28-Sep-14 3:00am

Thank you, Bill.
A dictionary is not for parsing, but for user if the getting values by keys with O(1) time complexity. Yes, it could be an overkill in case of small number of items, but still there is nothing wrong in it. Besides, imagine you aim to write the shortest code to illustrate this parsing, without compromising generalization...
—SA

BillWoodruff 28-Sep-14 3:16am

Not to belabor this discussion, but, the resulting 'Groups 'found by the RegEx can be stored easily in some structure, or parsed further and stored in a Dictionary structure.

My "bias" against RegEx probably comes from my experience at Adobe where I'd run into undocumented RegEx's that were quite complex and essentially functioned as "black-boxes" that people were afraid to tamper with.

And, of course, I am prejudiced against any formalism I have been too lazy to learn well, since that obviates my guilt, and excuses me from hard-work :)

Sergey Alexandrovich Kryukov 28-Sep-14 3:34am

I am almost sure that anything invented for this particular task using Regex (more exactly, using Regex along, not, say, Regex in combination with something like string.Split, which would make more sense), would be more complicated.

Besides, your impression on Regex is not only your impression. Not trying to deny the value of Regex, it's good to remember that it is notoriously easy to read and hard to write. In practice, it's important to feel the boundary when more and more complex task makes the solution quite feasible, but overly complex to be practical. After all, simple ad-hoc parsing is not rocket science to take it too seriously, and, from the other hand, general parsing does not use anything like Regex at all...

—SA