CODEWITHSUNDEEP
c#
Karim
Karim

Reputation: 6283

How do I call a function that expects a Byte[][][] parameter?

What kind of variable should I initialize and how do I do it?

For example 

byte[][][] data = ?????;

The function is from LibJpeg.NET library. The function definition is 

Int32 jpeg_read_raw_data (
    Byte[][][] data,
    Int32 max_lines
)

There is no good documentation for this function, so I don't know what to send it, but I want to try to send something and see what the function will return.

The problem is that I don't know how to call it.

Upvotes: 1

Views: 281

Answers (4)

Firoso
Firoso

Reputation: 6685

byte[][][] data is a 3 dimensional array, allocate it accordingly

= {{{0,1,2}{3,4,5}{6,7,8}}
   {{0,1,2}{3,4,5}{6,7,8}}
   {{0,1,2}{3,4,5}{6,7,8}}}

NOTE! THIS WILL NOT WORK! This is a jagged array, so unless you define data as byte[3,3,3] then you are going to go nowhere.

It occurred to me: I have no idea why you are using this library. Is there a reason the built in .NET JPEG classes aren't sufficient? If so, I imagine there would be a way to use the LibJpeg.NET library to get a byte stream from a file and arrange it into a 3D array. This seems like a very "hacky" way to do this, and it makes me wonder if it's just a port of a C library with no updates to fit into a framework like .NET or even OOP.

Upvotes: 2

Callum Rogers
Callum Rogers

Reputation: 15829

Just to correct firoso's answer, you can allocate arrays like that, he just has not specified the types as required in C# (His code would work in Java, AFAIK)

private byte[][][] lol =
        {
            new[]
                {
                    new byte[] {0, 1, 2},
                    new byte[] {3, 4, 5},
                    new byte[] {6, 7, 8}
                },
            new[]
                {
                    new byte[] {0, 1, 2},
                    new byte[] {3, 4, 5},
                    new byte[] {6, 7, 8}
                },
            new[]
                {
                    new byte[] {0, 1, 2},
                    new byte[] {3, 4, 5},
                    new byte[] {6, 7, 8}
                }
        };

The new[] is actually a shortcut for new byte[][] and the new byte[] cannot be shortened to new[] as then the compiler infers the numbers types as int.

I would not recommend using this method if you can use Heinzi's iterative method instead; I am only pointing out it is possible to allocate multidimensional arrays like this (it is good for a lot of specific data).

Upvotes: 1

Dirk Vollmar
Dirk Vollmar

Reputation: 176169

After a short look into the sources of LibJpeg.NET it looks like you should initialize the first dimension of the data array with the number of scan lines:

byte[][][] data = new byte[max_lines][][];

The rest of the array is filled when reading the raw data.

I'm not too familiar with that API so I don't know how you would get the number of scan lines though.

Upvotes: 1

Heinzi
Heinzi

Reputation: 172280

byte[][][] is an array of (arrays of (arrays of bytes)), also called a jagged array. It's not the same as a three-dimensional array (e.g. byte[,,] x = new byte[10,5,3];).

Here is an example for allocating and initializing such a structure:

        byte[][][] a = new byte[10][][];
        for (int i = 0; i < 10; i++)
        {
            a[i] = new byte[5][];
            for (int ii = 0; i < 5; i++)
            {
                a[i][ii] = new byte[3];
                a[i][ii][0] = 42;
                a[i][ii][1] = 52;
                a[i][ii][2] = 62;
            }
        }

Oh, and by the way, here's a related question: C# 3 dimensional array definition issue.

And here's the MSDN entry on jagged arrays: http://msdn.microsoft.com/en-us/library/2s05feca.aspx.

Upvotes: 2

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