roboa1983

Hi
In the program I'm writing, I have the option of either calling malloc three times to assign memory X to each, or calling malloc once by assigning memory 3*X, and do it by assigning a pointer to a pointer. \
I was trying to find what was the time dependence of these processes, or if it mattered at all.
Do you have any pointers?
Thanks

Salem

I'd suggest you go for what makes the code easiest to read in the first instance.

Yes there will be a time difference, but unless you're doing this 1000's of times in a loop, it's going to be hard to measure.

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roboa1983

Thanks Salem
I had gone with the easist to read part, but was worried there was a significance difference.

Elysia

The typical rule is to not over-optimize. Make your program as easy to guess and read as possible. If you find it slow, then use a profiler to find the bottlenecks and then optimize them.
Good to remember.

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C_ntua

Well, I don't know what you mean exactly. But keep in mind that calling multiple malloc() isn't a matter about timing. It is most important a matter of allocating continuous space.
If you call malloc() three times you won't get a continuous space which may case programs to run slower (once I had that issue in a project). If you call once malloc() with a 3*X as you said then you get a continuous space of memory, which will have benefits.

But depends of what you want to do

Elysia

It's easier to call malloc 3 times, and unless you really need the speed of calling it once (3X memory), then you should go with the former.
If you find out later that it's eating too much time, THEN go back and change it.

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QuantumPete

If your system supports it, you can use gethrtime() to time function calls. Just remember that running the code once one way and once another will not give you an accurate timing comparison. You'll need to run it a couple of hundred times to get average timings.

QuantumPete

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roboa1983

Thanks for the replies. I'm doing some timings with the original call (calling malloc three times), since it's either to understand. I'll look at the other technique later on, should other problems arise.

matsp

First of all malloc is not a function that takes the same time each time - sometimes it takes longer than other times. How much, and how often depends on the individual implementation of malloc. But for the general rule and averaged over many calls, it's not an overly long function. Unless you are mallocing really small blocks of memory, it's probably many times longer to fill the data into the allocated block than the overhead of the malloc call. Malloc is, generally speaking, a fairly well optimized function, since it is use by most applications, and at least some of that use would be in performance critical code.

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Mats

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