Easiest way to read single int from front of string

Question

I have an input string that looks something like this:

4 Bob 32 Joe 64 Sue 123 Bill 42

Where the 4 indicates the number of string integer pairs to follow. My current way of processing this looks something like this:

var strings = input.Split(' ');
int count = Int32.Parse(strings[0]);
for ( int i = 0; i < count; i++ )
{
  string name = strings[count*2 + 1];
  int number = Int32.Parse(strings[count*2 + 1]);
  ProcessPerson(name, number);
}

This feels quite cumbersome. Is there some library in C# that can wrap a string and give me services like "readInt" and "readString". I would ultimately like to have something like:

int count = input.ReadInt();
for(int i = 0; i<count; i++)
{
  ProcessPerson(input.ReadString(), input.ReadInt());
}

It doesn't look like that much of an improvement in this case, but my actual object model is a bit more complicated. I know other languages have facilities to o things like this, but I can't recall any .net libraries to simply read from the front of a string.

Do you have some knowledge of Regular Expressions? Something like ((\d+) ([a-zA-Z]+))+ could do the work for you... Just let me know if you want an example. Maybe you're looking for another solution :) — Oscar Mederos
– Oscar Mederos, Commented Jun 20, 2011 at 23:00
You need a class similar to Java's Scanner, you can see the base for that kind of class in stackoverflow.com/questions/722270/… — Marcelo
– Marcelo, Commented Jun 20, 2011 at 23:06
For this simple example the regex would work, but yes, I am looking for something more like java's scanner. — captncraig
– captncraig, Commented Jun 20, 2011 at 23:09

svick · Accepted Answer · 2011-06-20 23:21:41Z

You could easily write such a “library” yourself:

class Parser
{
    private readonly Queue<string> m_parts;

    public Parser(string s)
    {
        m_parts = new Queue<string>(s.Split(' '));
    }

    public string ReadString()
    {
        return m_parts.Dequeue();
    }

    public int ReadInt32()
    {
        return int.Parse(ReadString());
    }
}

If the string could be large, or you are reading it from a stream, you have to do the splitting yourself:

class StreamParser
{
    private readonly TextReader m_reader;

    public StreamParser(string s)
        : this(new StringReader(s))
    {}

    public StreamParser(TextReader reader)
    {
        m_reader = reader;
    }

    public string ReadString()
    {
        var result = new StringBuilder();
        int c = m_reader.Read();
        while (c != -1 && (char)c != ' ')
        {
            result.Append((char)c);
            c = m_reader.Read();
        }

        if (result.Length > 0)
            return result.ToString();

        return null;
    }

    public int ReadInt32()
    {
        return int.Parse(ReadString());
    }
}

Abe Miessler · Accepted Answer · 2011-06-20 23:02:19Z

1

This is probably a little better:

var strings = input.Split(' ');
for ( int i = 2; i < strings.length; i + 2 )
{
  ProcessPerson(strings[i - 1], Int32.Parse(strings[i]));
}

answered Jun 20, 2011 at 23:02

Abe Miessler

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6 Comments

rid Over a year ago

Plus, you don't need that number at position 0 to tell you how many items there are, you can simply find that out by dividing the length of the array by 2.

Abe Miessler Over a year ago

I thinking just using the length of the array would make sense, wouldn't it? I've adjusted my answer to reflect that.

captncraig Over a year ago

Maybe I didn't use the best example. My actual object graph is quite a bit more complicated and requires the use of the count. I really want to read a single value from the front of an string buffer. My workaround is to keep a list and continually remove the front element, but that feels hackish.

Abe Miessler Over a year ago

That feels hacking to me too. You can always have access to count based on the length of strings and you will always be able to figure out your position in the array using i. Is there something that the above can't do that you need?

Abe Miessler Over a year ago

In what situation would a valid input be provided where an off-by-one error would occur?

|

Oscar Mederos · Accepted Answer · 2011-06-20 23:16:37Z

I suggest you using Regular Expressions for that purpose. Here is an example:

string input = "4 Bob 32 Joe 64 Sue 123 Bill";
var matches = Regex.Matches(input, @"(?:(\d+) ([a-zA-Z]+))+");
for (int i = 0; i < matches.Count; i++)
{
    Console.WriteLine("Number: {0} \t Person: {1}", matches[i].Groups[1], matches[i].Groups[2]);
}

will print:

Number: 4        Person: Bob
Number: 32       Person: Joe
Number: 64       Person: Sue
Number: 123      Person: Bill

When using Regular Expressions, all you need to know is how to express the pattern you want to match. In this case, you want to match:

[Number][Space][Letters] one or more times, right? That's exactly what it means:
(\d+) ([a-zA-Z]+)

Edit 1:
In this moment, I don't really know if you want to associate to each person the number that is before or after each one, but all you have to do is swap the above pattern, so it will become:

(?:([a-zA-Z]+) (\d+))+

Edit 2:
If you want to skip the first number, you can use this pattern:

\d+ (?:([a-zA-Z]+) (\d+))+

so you're matching a number (\d+), then a space (), and then the same you were matching before (Name Number Name Number ...)

@AbeMiessler That's not a problem at all. I just gave him an example. I will edit my answer just in case he wants to skip it.

Rebecca Scott · Accepted Answer · 2011-06-20 23:17:03Z

Try reading from a queue, it could be a bit cleaner:

var s = "4 Bob 32 Joe 64 Sue 123 Bill 42";
var queue = new Queue(s.Split(' '));
var count = Convert.ToInt32(queue.Dequeue());
while (queue.Count != 0)
{
    var name = queue.Dequeue();
    var number = Convert.ToInt32(queue.Dequeue());
    ProcessPerson(name, number);
}

If you add extension methods to Queue you can simplify this further (untested):

public static class QueueExtensions {
    public static int DequeueInt(this Queue<string> queue) {
        return Convert.ToInt32(queue.Dequeue());
    }
}

ProcessPerson(queue.DequeueInt(), queue.Dequeue());

You should add all kinds of guards in there as well to avoid trying to dequeue an empty queue and invalid conversions.

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