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Casting or type conversion question

Started by codingJoe Feb 20, 2020 at 3:22 PM 5 replies 2.2k views

Original Post

Feb 20, 2020 at 3:22 PM

Hello,

can someone explain me if there are differences in execution speed between following 3:

int a=3;
size_t b=(size_t)a;
size_t b=size_t(a);
size_t b=static_cast<size_t>(a);

I am pretty much sure that there is no difference between #1 and #3. But for #2, doesn't that add an overhead because of the constructor?

And what about following example?

unsigned char* a=aRandomBuffer;
float b=((float*)a)[0];
float b=(reinterpret_cast<float*>(a))[0];

Thanks for any insight!

a light breeze

Feb 20, 2020 at 3:33 PM

There should not be any difference in execution speed in either example. The compiler will almost certainly generate the exact same code for all three cases in the first example, and for both cases in the second example.

codingJoe

Feb 20, 2020 at 8:09 PM

Thanks for the clarification!!

Adam_42

Feb 20, 2020 at 8:58 PM

It easy to try out these types of things and examine the assembly yourself: https://godbolt.org/z/nGiDQu

DoomOperator

Feb 20, 2020 at 9:25 PM

@codingjoe I heard casting is less reliable, i also read some of this if you wish to find out more about the reliability of casting. There is a lot of great explaining of how casts operate here.

please like if useful.

https://stackoverflow.com/questions/4167304/why-should-casting-be-avoided

fleabay

Feb 20, 2020 at 10:17 PM

DoomOperator said:
please like if useful.

I've heard that it's not useful.

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