Fast and efficient way to read a space separated file of numbers into an array?

Question

I need a fast and efficient method to read a space separated file with numbers into an array. The files are formatted this way:

4 6
1 2 3 4 5 6
2 5 4 3 21111 101         


        

Answer 1

How about:

    static void Main()
    {
        // sample data
        File.WriteAllText("my.data", @"4 6
1 2 3 4 5 6
2 5 4 3 21111 101
3 5 6234 1 2 3
4 2 33434 4 5 6");

        using (Stream s = new BufferedStream(File.OpenRead("my.data")))
        {
            int rows = ReadInt32(s), cols = ReadInt32(s);
            int[,] arr = new int[rows, cols];
            for(int y = 0 ; y < rows ; y++)
                for (int x = 0; x < cols; x++)
                {
                    arr[y, x] = ReadInt32(s);
                }
        }
    }

    private static int ReadInt32(Stream s)
    { // edited to improve handling of multiple spaces etc
        int b;
        // skip any preceeding
        while ((b = s.ReadByte()) >= 0 && (b < '0' || b > '9')) {  }
        if (b < 0) throw new EndOfStreamException();

        int result = b - '0';
        while ((b = s.ReadByte()) >= '0' && b <= '9')
        {
            result = result * 10 + (b - '0');
        }
        return result;
    }

Actually, this isn't very specific about the delimiters - it'll pretty much assume that anything that isn't an integer is a delimiter, and it only supports ASCII (you use use a reader if you need other encodings).