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Consequences of only using stack in C++

Asked 2010-09-12T14:15:33.237
17

Lets say I know a guy who is new to C++. He does not pass around pointers (rightly so) but he refuses to pass by reference. He uses pass by value always. Reason being that he feels that "passing objects by reference is a sign of a broken design".

The program is a small graphics program and most of the passing in question is mathematical Vector(3-tuple) objects. There are some big controller objects but nothing more complicated than that.

I'm finding it hard to find a killer argument against only using the stack.

I would argue that pass by value is fine for small objects such as vectors but even then there is a lot of unnecessary copying occurring in the code. Passing large objects by value is obviously wasteful and most likely not what you want functionally.

On the pro side, I believe the stack is faster at allocating/deallocating memory and has a constant allocation time.

The only major argument I can think of is that the stack could possibly overflow, but I'm guessing that it is improbable that this will occur? Are there any other arguments against using only the stack/pass by value as opposed to pass by reference?

c++ pass-by-reference pass-by-name
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Subtyping-polymorphism is a case where passing by value wouldn't work because you would slice the derived class to its base class. Maybe to some, using subtyping-polymorphism is bad design?

answered 2010-09-12T15:02:05.603
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The only major argument I can think of is that the stack could possibly overflow, but I'm guessing that it is improbable that this will occur? Are there any other arguments against using only the stack/pass by value as opposed to pass by reference?

Well, gosh, where to start...

  1. As you mention, "there is a lot of unnecessary copying occurring in the code". Let's say you've got a loop where you call a function on these objects. Using a pointer instead of duplicating the objects can accelerate execution by one or more orders of magnitude.

  2. You can't pass a variable-sized data structures, arrays, etc. around on the stack. You have to dynamically allocate it and pass a pointers or reference to the beginning. If your friend hasn't run into this, then yes, he's "new to C++."

  3. As you mention, the program in question is simple and mostly uses quite small objects like graphics 3-tuples, which if the elements are doubles would be 24 bytes apiece. But in graphics, it's common to deal with 4x4 arrays, which handle both rotation and translation. Those would be 128 bytes apiece, so if a program that had to deal with those would be five times slower per function call with pass-by-value due to the increased copying. With pass-by-reference, passing a 3-tuple or a 4x4 array in a 32-bit executable would just involve duplicating a single 4-byte pointer.

  4. On register-rich CPU architecures like ARM, PowerPC, 64-bit x86, 680x0 - but not 32-bit x86 - pointers (and references, which are secretly pointers wearing fancy syntatical clothing) are commonly be passed or returned in a register, which is really freaking fast compared to the memory access involved in a stack operation.

  5. You mention the improbability of running out of stack space. And yes, that's so on a small program one might write for a class assignment. But a couple of months ago, I was debugging commerc

answered 2010-09-12T16:41:02.043

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