Array Manipulation ... made simpler?

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Hey,

Quick question, and feel free to just point me at a class or FAQ. Is there a faster or more efficient way to do the following? Just slide values down an array:

int a[5] = {1, 2, 5, 2, 1};

a[4] = a[3];
a[3] = a[2];
a[2] = a[1];
a[1] = a[0];

a[0] = //Some input

I'm just looking for a way to slide all the values down by 1 place. Thanks in advance for answering my trivial question.

Posted 7-Apr-11 8:55am

Donald Hume

Updated 7-Apr-11 10:13am

v2

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5 solutions

Solution 1

Use a collection instead of an array. If you can't do that, allocate a new array that's one element larger, and then move the other array into the new one starting at element 1 in the new array.

Posted 7-Apr-11 8:57am

#realJSOP

Solution 3

If you use a fixed size array - use a circular seek pointer and you must not move anything. Thats the fastest method ever.
Regards.

Posted 7-Apr-11 10:24am

mbue

Solution 4

You could simply use memmove (or memmove_s) with the source starting at element [0] and the destination starting at element [1].

Good luck.

Posted 7-Apr-11 10:52am

krmed

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CPallini · Accepted Answer · 2011-04-07T09:47:00

Solution 2

There is the oldie-goldie memmove[^]:

C++

#include <cstring>
  //...
  int a[5] = {1, 2, 5, 2, 1};
  memmove(&a[1], &a[0], sizeof(a)-sizeof(a[0]));

Posted 7-Apr-11 9:47am

CPallini

Updated 7-Apr-11 15:14pm

v2

Comments

Donald Hume 7-Apr-11 16:13pm

Oh man what a silly mistake, anyway I fixed it for clarity's sake.

Pallini is that method any more efficient than just moving it myself?

CPallini 7-Apr-11 21:13pm

OK, I removed the first part of my answer according.
As about the performance, see Nish's replay. It makes sense to me.

Nish Nishant · Accepted Answer · 2011-04-07T14:02:00

Calls like memmove will most likely be optimized to take advantage of block-memory move intrinsic operations, although a decent compiler would see your for-loop (or sequential code, whatever you have), and replace it with a memmove during compilation. You could run some performance tests if this is a major factor, although if it's just a few hundred or even 1000 elements you are talking about, it probably does not matter much.