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I am a newbie to Cocoa Programming and I have a question concerning data buffers.

The obvious one is of course, what is a data buffer? Many of the APIs have function calls which have arguments that are pointers to a buffer of data. Can someone plese tell me what a buffer of data really means? How do you create one?

Does opening a file, for example an image file, or a sound file, mean that the program creates a buffer of data of the file that was opened?

Any clarifications would be really helfpul in getting me to understand how Cocoa programming works.



Often, it’s an unsigned char array, or another type of array (such as short, etc). It depends on the size of the data.

Buffers, when used in Cocoa, are generally normal C data types. If you don’t know C, then you should go read up on C because you won’t really know how to work with them, since you need to know how C pointers work in order to access the data inside a buffer.

For example, if you have an NSData object, you can get the raw data inside it via the bytes method. This method will return const void *, which you should then typecast to another C data type. If you wanted to access every 2 bytes inside this data, you could do something like this:

NSData *myData = [NSData dataWithContentsOfFile:someFile]; const unsigned short *rawData = (unsigned short)[myData bytes];

This will take every 2 bytes from myData and put it into an unsigned short array. The length of rawData would be [myData length]/2 since you’re getting every 2 bytes ( length returns the number of bytes). Since this is a normal C pointer, you can use the [] syntax to get data at a certain index.

Hope this helps!

Hey, thanks a lot. That definitely was illuminating.

I do have experience with C so I was able to follow what you said.

Thanks again.