repetition and variables : declaring and assigning

technomeister · 02-11-2010, 09:50 AM

Take the following scenario :

A function which is called multiple times, and in it, a value is assigned to a variable.

The question : Is it more efficient to declare the variable only once and simply assign it on each iteration, versus declaring and assigning each time? Logic would suggest that the answer is yes, so I guess my question is really : is the difference worth talking about?

rn_ · 02-11-2010, 10:06 AM

depends on the application really. If it's a high-level user app, you won't see any difference, however it's probably not good practice to keep creating the var over and over again in each iteration. But, if it's a low-level, kinda down to the firmware level driver-type code, then you'll probably want to optimize it.

smeezekitty · 02-11-2010, 01:16 PM

Do you mean:

Code:

int i;
while(?){
i = 6;
}

VS

Code:

while(?){
int i = 6
}

?
If so, there will be NO difference if the compiler has an optimizer built in.

smeezekitty · 02-11-2010, 01:16 PM

Double post.

MTK358 · 02-11-2010, 01:24 PM

I was also wondering about that.

Anyway, which one is more efficient if not optimized (just curious)?

And does gcc optimize this by default?

technomeister · 02-12-2010, 10:23 AM

Quote:

Originally Posted by smeezekitty

Do you mean:

Code:

int i;
while(?){
i = 6;
}

VS

Code:

while(?){
int i = 6
}

?

Yes, exactly.

Quote:

depends on the application really. If it's a high-level user app, you won't see any difference, however it's probably not good practice to keep creating the var over and over again in each iteration. But, if it's a low-level, kinda down to the firmware level driver-type code, then you'll probably want to optimize it.

That's what I thought... That it's probably best practice to declare only once, but in reality isn't going to make much, if any, difference.