Thread: how to make format...

A file format is just a convention. The program is expecting the file to be in a specific format, which information lined up perfectly. For example, programs written in Java have 0xCAFEBABE as a number at the start of each .class file. This is how Java knows it's a valid .class file.

Programs can only files in the format they expect them to be.

It's just like writing a normal program that gives and receives input at the command line. If you ask the user for a number, and they enter "bleh" at the command line, what should your program do? Same concept.

And there's nothing preventing someone from using an extension that's already been taken. Plug something into filext.com and you'll see what I mean. For example: http://filext.com/file-extension/1

Originally Posted by hockey97

so it's nothing but how the file's data is structured??

How would you create such files like if you were to make your own format??

like if you make your own do you get to put your own .somthing extensions??
for the file.

then make a program that will accept that format??

Right.

How would you design your own format? Well, there are a few things you'd want to keep in mind. The first is how are you going to distinguish this file type? Many file formats have a "signature", which is often a few characters at the beginning of the file indicating the format of the file. For example, a file's first two characters have to be "MZ" for Windows to consider it executable.

As another example, PNG image files have an eight-byte signature. It's quite ingenious, really. It contains "PNG", so you know what it is just by looking at it. It also contains the DOS EOF character ^Z (26 decimal), so that if you type a PNG file from a DOS terminal, nothing will be printed beyond that. It's a nice feature, because PNG files are binary files and it wouldn't look nice on a terminal (plus you might miss the signature). It also contains an extended byte, that is, a byte that utilizes all eight bits. This is important for binary files, because if the file was transferred over a 7-bit connection, with the MSB discarded (would would be just fine for most text files), the PNG file would be messed up. Well, so would the signature, because it wouldn't be transferred properly. So just by looking at the signature a PNG reader can tell how it was transferred.

Here's information on the PNG signature: http://www.libpng.org/pub/png/spec/1...Structure.html

I really like the PNG format (can you tell? ), so I'll emphasize another important point with it: file formats have to be extensible. Inevitably, you're going to create a new version of the file format. What will you do then? Will you change the extension and go .format2, which is annoying? Will you use the same extension and have old versions of programs that process the format mess up on them? (If you used a signature, you could always change it. )

PNG files are organized into blocks of a certain size. I won't go into details, but basically each block is of a certain type. If the reader doesn't recogize the block type, it can check a flag to see if the block is important. If the block is important, it can exit with an error message; but if it isn't, it can just ignore it and keep reading, safe in the knowledge that it can probably get the gist of the file without understanding that block.

You don't have to do that -- it's just meant to be an example. PNG files are very extensible, so that when they come out with the next version, everyone won't have to upgrade their programs.

[edit] Note that all of this PNG stuff is from memory, I may have misrepresented a few of the details. [/edit]

You can register a format with Windows so that it will open with a certain program, and you can choose the icon, etc, if that's what you mean. Try Start->Control Panel->Folder Options->File types (for XP).

I am making a computer system from gound up like buying components ect and making a computer system, I want to make my own file system, and OS for it.
and all files are to be created with my own formats.

I am trying to learn the overall system of a computer so doing step by step, learning the stuff.

if their are any tips or websites that would guide me in something what I am doing or at least have concepts of comptuers, where I could learn or help me along the way on building a computer system.

Just so you know, creating your own operating system is virtually impossible. It's the work of years for extremely good programmers.

You might be able to do something easier, however, such as create your own shell, for example. Your shell might support certain commands, and handle certain file extensions differently. The nice thing about making something like this is that you can use the ordinary Windows console window for it.