Is there an equivalent to the Scanner class in C# for strings?

Question

In Java I can pass a Scanner a string and then I can do handy things like, scanner.hasNext(), or scanner.nextInt(), scanner.nextDouble(), etc.

This allows some pretty clean code for parsing a string that contains rows of numbers.

How is this done in C# land?

If you had a string that say had:

"0 0 1 22 39 0 0 1 2 33 33"

In Java I would pass that to a scanner and do a

while(scanner.hasNext()) 
    myArray[i++] = scanner.nextInt();

Or something very similar. What is the C#'ish way to do this?

Answer 1

While this isn't the exact same fundamental concept, what you're looking for can be done with this lambda expression:

string foo = "0 0 1 22 39 0 0 1 2 33 33";

int[] data = foo.Split(' ').Select(p => int.Parse(p)).ToArray();

What this does is first Split the string, using a space as a delimiter. The Select function then allows you to specify an alias for a given member in the array (which I referred to as 'p' in this example), then perform an operation on that member to give a final result. The ToArray() call then turns this abstract enumerable class into a concrete array.

So in this end, this splits the string, then converts each element into an int and populates an int[] with the resulting values.

Answer 2

To my knowledge, there are no built in classes in the framework for doing this. You would have to roll your own.

That would not be too hard. A nice C# version might implement IEnumerable so you could say:

var scanner = new Scanner<int>(yourString);
foreach(int n in scanner)
    ; // your code

Answer 3

I would do this in one of a couple ways depending on whether 1) you are using the latest .NET framework with LINQ support and 2) you know the values are valid integers. Here's a function to demonstrate both:

  int[] ParseIntArray(string input, bool validateRequired)
  {
     if (validateRequired)
     {
        string[] split = input.Split();
        List<int> result = new List<int>(split.Length);
        int parsed;
        for (int inputIdx = 0; inputIdx < split.Length; inputIdx++)
        {
           if (int.TryParse(split[inputIdx], out parsed))
              result.Add(parsed);
        }
        return result.ToArray();
     }
     else
        return (from i in input.Split()
                select int.Parse(i)).ToArray();
  }

Based on comments in other answer(s), I assume you need the validation. After reading those comments, I think the closest thing you'll get is int.TryParse and double.TryParse, which is kind of a combination of hasNextInt and nextInt (or a combination of hasNextDouble and nextDouble).

Answer 4

You could use linq to accomplish this like so:

string text = "0 0 1 22 39 0 0 1 2 33 33";
text.Where(i => char.IsNumber(i)).Write(); // do somthing usefull here...

Answer 5

To get as close as possible to your syntax, this'll work if you're only interested in one type ("int" in the example):

static void Main(string[] args)
{
   if (args.Length == 0) { args = new string[] { "3", "43", "6" }; }
   IEnumerator<int> scanner = (from arg in args select int.Parse(arg)).GetEnumerator();
   while (scanner.MoveNext())
   {
      Console.Write("{0} ", scanner.Current);
   }            
}

Here's an even more whiz-bang version that allows you to access any type that is supported by string's IConvertible implementation:

static void Main(string[] args)
{
    if (args.Length == 0) { args = new string[] { "3", "43", "6" }; }
    var scanner = args.Select<string, Func<Type, Object>>((string s) => {
            return (Type t) =>
            ((IConvertible)s).ToType(t, System.Globalization.CultureInfo.InvariantCulture); 
        }).GetEnumerator();
    while (scanner.MoveNext())
    {
        Console.Write("{0} ", scanner.Current(typeof(int)));
    }            
}

Just pass a different type to the "typeof" operator in the while loop to choose the type.

These both require the latest versions of C# and the .NET framework.

Answer 6

I'm going to add this as a separate answer because it's quite distinct from the answer I already gave. Here's how you could start creating your own Scanner class:

class Scanner : System.IO.StringReader
{
  string currentWord;

  public Scanner(string source) : base(source)
  {
     readNextWord();
  }

  private void readNextWord()
  {
     System.Text.StringBuilder sb = new StringBuilder();
     char nextChar;
     int next;
     do
     {
        next = this.Read();
        if (next < 0)
           break;
        nextChar = (char)next;
        if (char.IsWhiteSpace(nextChar))
           break;
        sb.Append(nextChar);
     } while (true);
     while((this.Peek() >= 0) && (char.IsWhiteSpace((char)this.Peek())))
        this.Read();
     if (sb.Length > 0)
        currentWord = sb.ToString();
     else
        currentWord = null;
  }

  public bool hasNextInt()
  {
     if (currentWord == null)
        return false;
     int dummy;
     return int.TryParse(currentWord, out dummy);
  }

  public int nextInt()
  {
     try
     {
        return int.Parse(currentWord);
     }
     finally
     {
        readNextWord();
     }
  }

  public bool hasNextDouble()
  {
     if (currentWord == null)
        return false;
     double dummy;
     return double.TryParse(currentWord, out dummy);
  }

  public double nextDouble()
  {
     try
     {
        return double.Parse(currentWord);
     }
     finally
     {
        readNextWord();
     }
  }

  public bool hasNext()
  {
     return currentWord != null;
  }
}