[Pro Patria Finland]

An interesting question occured somewhere, I am not even sure if this question makes sense. Anywho, does anyone know which of these is the fastest one to execute, to make an infinite loop (in C++)?

while(1)
{

}

for(;;)
{

}

hello:

goto hello;

It doesn't matter what's inside the loop, just what of those is the fastest one to execute.

[Sean D]

they all compile down into the same machine code

[Jheshka]

If there was one that's faster. I would think that for loops would be faster.




But what Sean D said sounds pretty accurate to me.

[Hawk552]

Originally Posted by Jheshka If there was one that's faster. I would think that for loops would be faster. But what Sean D said sounds pretty accurate to me.

Hey man, the Agents have been looking for you. Hit me up on MSN later.

Also, the while loop is the fastest. The for loop as you put it won't work because there's no condition for continuation.

[Pro Patria Finland]

Originally Posted by Hawk552 Hey man, the Agents have been looking for you. Hit me up on MSN later. Also, the while loop is the fastest. The for loop as you put it won't work because there's no condition for continuation.

The for(;;) loop works fine. I even tested it again.

#include <iostream>

int main()
{
    for(;;)
        std::cout << "0";

    return 0;
}

Compiles and works.

Sean D: Based on what? Your knowledge as an experienced programmer? Could you provide some source? I am not asking to be an asshole. I am genuinely interested.

Edit: Reason why I am intersted is, that when programming for embedded systems the programs have to be as small as possible. I know this is a small matter, but I like to write as highly optimized code as possible for this project. In all of the examples I find in the micro-controllers datasheet a for(;;) loop is used.

[Hawk552]

Interesting, I never knew that. Doesn't make sense, but oh well.

[Exolent[jNr]]

I agree with Hawk that the while() loop would be faster than the for() loop, but I can't compare with the goto because I'm not sure how fast it works.

[Hawk552]

Originally Posted by Exolent[jNr] I agree with Hawk that the while() loop would be faster than the for() loop, but I can't compare with the goto because I'm not sure how fast it works.

Goto is slower because it has to seek to a place that could possibly involve re-entry. I'm not totally sure about how it acts in C(++) but in TI-BASIC it's the worst thing you can do, several orders of magnitude slower than a for/while loop.

BTW, the reason I think the while loop would be faster is that it only takes 1 parameter. A for loop is basically a while loop that has 2 extra parameters (action after each iteration and action prior to first iteration), so there's no reason a for loop would be faster.

[danielkza]

Originally Posted by Hawk552 Goto is slower because it has to seek to a place that could possibly involve re-entry. I'm not totally sure about how it acts in C(++) but in TI-BASIC it's the worst thing you can do, several orders of magnitude slower than a for/while loop. BTW, the reason I think the while loop would be faster is that it only takes 1 parameter. A for loop is basically a while loop that has 2 extra parameters (action after each iteration and action prior to first iteration), so there's no reason a for loop would be faster.

As far as I know there's no such check in C++. Goto's translate directly to jump instructions in most cases.

And all the methods will generate the same machine code in any modern compiler.

[Sean D]

experience? sure i guess... as danielkza was getting at, any modern compiler is going to know that the condition is always true so it will compile down to a jump. how much code it takes in the language doesn't determine how fast the machine code is; modern compilers are pretty smart. if you want proof then compile each and disassemble the executables in ida. by the way, if you're trying to optimize your code, you really should be using a profiler to pinpoint the bottleneck of your software so you don't have to waste time guessing.

also don't listen to anything hawk says, he doesn't know what he's talking about