C# uses a lot of streams, or at least it seems so in some of the code examples I have looked at.
Having said that I felt the need to read up on the Stream class. The stream class is an abstract class and an abstract acts as a type of base class from which other classes can inherit. And just to recap, abstract methods do not have a method body and must be implemented by the class inheriting from it. A method marked as virtual can be overridden but it does not have to be implemented. Methods that are marked as abstract can be overriden.
So the stream class is an abstract base class for a set of other classes that do various operations such as reading content from files, reading files in a directory, etc. Each of the classes that inherit from the base stream class can be seen as a type of stream. Streams can be read from, written to and they support seeking.
The classes that inherit from the Stream class can be divided into three broad categories:
- Classes that are used for File I/O
- Classes that are used for reading and writing to streams
- Common IO stream classes
The reason for taking a look at these classes is because I was looking at a PowerPoint presentation recently. More specifically I was looking at PowerPoint 2007 (pptx) and its underlying XML. If you save a Powerpoint 2007 as XML and you look at the source you will note that there are sections called pkg:binaryData. It got me wondering that maybe that same binary data can be processed in C# code. Take a look at the following sample C# code:
Image img = Image.FromFile(@"C:\Users\fredrike\Documents\LEGAL SUITE.bmp");
byte[] myByte = File.ReadAllBytes(@"C:\Users\fredrike\Documents\LEGAL SUITE.bmp");
Console.WriteLine(myByte.Length);
MemoryStream stream = new MemoryStream(myByte);
int lengthOfByte = Convert.ToInt32(stream.Length);
byte[] mySecondByte = ReadFully(stream, lengthOfByte);
Console.WriteLine(mySecondByte.Length);
Image img2 = Image.FromStream(stream);
img2.Save(@"C:\Users\fredrike\Documents\LEGAL SUITE3.bmp");
Notice a couple of things I have done in the code. I created a Image class instance and read it from an existing bitmap image. I then create a byte array and used the static ReadAllBytes method supplied by the File class. I then just simply wrote the length of the file to the screen because in the next couple of lines I create a MemoryStream instance using the byte array, after which I also get the length property of the MemoryStream instance because I use it in a function called ReadFully:
public static byte[] ReadFully(Stream stream, int initialLength)
{
// If we've been passed an unhelpful initial length, just
// use 32K.
if (initialLength < 1)
{
initialLength = 32768;
}
byte[] buffer = new byte[initialLength];
int read = 0;
int chunk;
while ((chunk = stream.Read(buffer, read, buffer.Length - read)) > 0)
{
read += chunk;
// If we've reached the end of our buffer, check to see if there's
// any more information
if (read == buffer.Length)
{
int nextByte = stream.ReadByte();
// End of stream? If so, we're done
if (nextByte == -1)
{
return buffer;
}
// Nope. Resize the buffer, put in the byte we've just
// read, and continue
byte[] newBuffer = new byte[buffer.Length * 2];
Array.Copy(buffer, newBuffer, buffer.Length);
newBuffer[read] = (byte)nextByte;
buffer = newBuffer;
read++;
}
}
// Buffer is now too big. Shrink it.
byte[] ret = new byte[read];
Array.Copy(buffer, ret, read);
return ret;
}
I got this from Jon Skeet’s website. Be sure to check out his other C# articles. In my code I then created a second byte array which is generated by the ReadFully method. Once the bytes have finished reading I created a second Image instance, img2 and pass it the MemoryStream instance, and I then call img2′s Save method and create a second image based on the first one.
So my question is, can the binary data from Powerpoint presentations be used in the same way?
