Comments on: Memory Allocation for the budding Objective-C programmer

By: SSI

SSI — Wed, 05 Aug 2009 09:14:29 +0000

OR how to write at desired memory location(address) in C/C++?

By: SSI

SSI — Wed, 05 Aug 2009 09:11:14 +0000

Can any body tell me how to allocate a chunk of memory at desired memory address using malloc or any other function in C/C++?

By: kp

kp — Mon, 20 Jul 2009 00:02:45 +0000

oops. Right you are. My bad. Fixed now. That’s what happens when you copy and paste code.

By: umm...

umm... — Sun, 19 Jul 2009 22:29:11 +0000

To clarify on what Markus said, look at your post again…

It uses int *myInts = malloc(sizeof(CGPoint) * 50);

I’m guaranteed that’s a mistake.

By: kp

kp — Thu, 16 Jul 2009 23:21:38 +0000

Markus, array notation is magical. It knows how many bytes are in each element. You made your array as a pointer to int: int *myPoints

If you make it a pointer to CGPoint, you’ll be all set: CGPoint *myPoints.

By: Markus

Markus — Thu, 16 Jul 2009 22:34:04 +0000

“int *myPoints = malloc(sizeof(CGPoint) * 50);”

myPoints[0]= CGPointMake(100, 100);
myPoints[1]= CGPointMake(110, 110);
myPoints[2]= CGPointMake(120, 120);”

wouldn’t the [1] overwrite parts of the previous defined point? The compiler always increases the pointer by one byte using the brackets,
since it doesn’t have any information about of the size of each object.

so the correct syntax should be:
”
myPoints[0]= CGPointMake(100, 100);
myPoints[sizeof(CGPoint)]= CGPointMake(110, 110);
myPoints[sizeof(CGPoint)*2]= CGPointMake(120, 120);”

or did I miss something?

By: kp

kp — Sun, 12 Jul 2009 18:06:29 +0000

ok, well that is enticing.

By: jtgrassie

jtgrassie — Sun, 12 Jul 2009 18:04:18 +0000

With a STL Vector certainly.
The elements are guaranteed to be stored in contiguous storage locations. Just grab the pointer to the first element and pass that to GL functions requiring c array.

By: kp

kp — Sun, 12 Jul 2009 17:33:48 +0000

on the current project I’m working on, I’m heavily using primitive arrays as vector arrays for OpenGL drawing. I think this is a necessity because OpenGL takes pointers to various types of arrays directly. Could you use STL containers in that context, or would you need to convert them?

By: jtgrassie

jtgrassie — Sun, 12 Jul 2009 17:19:20 +0000

No offence taken Keith

The reason I highlight this is really because of one of the biggest strengths of Objective-C/C++, the fact you can mix C, C++ and Objective-C all together.
This allows you to use what’s best / most appropriate language for given problem. I don’t think there is any valid reason to disregard C++ usage in Objective-C, especially when it offers an elegant solution to a given problem.

For the specific problem you highlight – a mutable array of primitive types – an STL container really is the way to go.
If you really are going to bother describing malloc and free for a mutable array, you really should also describe realloc (which is what you are going to need to shrink and grow your array).
http://www.cplusplus.com/reference/clibrary/cstdlib/realloc/