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Very Simple Question

Started by Helicon56 Jun 13, 2002 at 12:22 PM 4 replies 150+ views

Original Post

Jun 13, 2002 at 12:22 PM

Hi, This is just something that''s been bugging me lately, and is very basic. Temprorary objects that are declared within a function...whats the memory management for them? void SwapVector(Vector &vec1, Vector &vec2) { Vector temp; temp = vec1; vec1 = vec2; vec2 = temp; } What happens for temp? Does it get allocated and freed every function call, or does it get allocated once and reused ever function call....or what? Sorry about how basic this is, i just thought i really should know the answer to something like that. Thanks anyway.

ktuluorion

Jun 13, 2002 at 12:26 PM

The memory for the variable temp will be reallocated each time the function is called.

Abominacion

Jun 13, 2002 at 12:30 PM

It will be allocated in the stack each time the function is called, don''t worry, it''s just a sub esp,4 or a push , there are no system calls involved.

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Cuando miras al abismo el abismo te devuelve la mirada.
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thona

Jun 13, 2002 at 12:43 PM

Furthermore it is ONE call for ALL objects at once. Basially the size of all objects used is allocated on the stack.

uNiQue0815

Jun 13, 2002 at 1:58 PM

yes... "allocated" in stack, all vars in one call, as everyone said before

if you WANT it to be a variable that is allocated ONCE and used for every function call (with the last value stored), you can declare it static :

..
static Vector temp;
..

after that it''s like a global variable, that''s only available in the function

Evil Bill

Jun 13, 2002 at 4:49 PM

However, the thing you need to watch is your constructors. Your default constructor for Vector will be called every time the function is called. To fix this use:

  
void SwapVector(Vector &vec1, Vector &vec2)
{
Vector temp(vec1);   // Copy constructor (if its defined)

vec1 = vec2;
vec2 = temp;
}

or use a static variable. Actually, ive seen several occasions where a static variable was used for non-primitive types in low-level functions like this. But i can''t think where.

HTH, Steve

Steve
DirectX Programmer
Soon to be the new Bill Gates

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