Inserting element in between in C array

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Inserting characters in the middle of char array

I need to insert element in between 2 elements in a static array. I have written the following code. Please let me know if we have more efficient code than this.

int main()
{
    int a[4];

    a[0] = 10;
    a[1] = 20;
    a[2] = 30;

    int x = 15;

    memcpy(a+2,a+1,2);

    a[1] = x;

    printf("%d",a[2]);
}

use memmove instead, for the overlapping issue. Also, you need to specify the length of the move in bytes, so 2 * sizeof(a[0]) — Mordachai, Jan 23 '13 at 22:33
If you move *anything* within 16 bytes, efficiency is no concern. This is going to take about 0.000000001 seconds anyway. — Bo Persson, Jan 23 '13 at 22:36
@BoPersson ...Hi ...how did you find out the number 16 Bytes? or is that the array size in bytes — Anup Buchke, Jan 23 '13 at 22:38
@anup - Yes, you have four `int`'s about 4 bytes each. I think you are worrying about the wrong things. Computers are **fast**. — Bo Persson, Jan 23 '13 at 22:40
@Mark B: `vector` and `deque` aren't available in C. @anup.stackoverflow: An int may very well be 1 byte, providing CHAR_BIT >= 16. — autistic, Jan 23 '13 at 22:47
@modifiablelvalue: I see no reason to believe the OP is limited to C, it wasn't he who removed the C++ tag. — Benjamin Lindley, Jan 23 '13 at 22:51
@BenjaminLindley Oh. I apologise, I didn't see any C++ tag. :/ — autistic, Jan 23 '13 at 22:55

score 1 · Answer 1 · edited May 23 '17 at 10:24

You are worrying too much about low level optimizations - the compiler takes care of that.

If believe the most obvious code is also the fastest in this case:

a[3] = a[2];
a[2] = a[1];
a[1] = x;

You can't get it simpler than that.

Here is an example of what the compiler can do when optimizing code:

https://stackoverflow.com/a/11639305/597607

(10 lines of source code turned into 4-5 machine instructions - just let the compiler do its work!).

Inserting element in between in C array

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