Re: fast array copy c++

From:

Pete Becker <pete@versatilecoding.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 21 May 2008 10:09:51 -0400

Message-ID:

<2008052110095116807-pete@versatilecodingcom>

On 2008-05-21 09:05:28 -0400, Zeppe
<zep_p@remove.all.this.long.comment.yahoo.it> said:

utab wrote:

On Wed, 21 May 2008 05:46:29 -0700, fr33host wrote:

Dear developers,
I have a question. Is there a faster array copy than a for loop. What
would you suggest for this code sample?

void get(char* src, char* dest, int i) {
    for (int j = 0; j < recordLen; j++, i++) {
        dest[j] = src[i];
    }
}

Thank you for int main()

An option:

  std::string source("COPY THIS STRING WITH STL COPY");
  std::string dest;
  copy(source.begin(),source.end(),back_inserter(dest));
  std::cout << dest << std::endl;
  return 0;

this is slower because it doesn't take advantage of knowing the size of
the destination in advance.

An STL implementation of the for cycle is:

std::fill(src, src + recordLen, dest);

fill takes a value, not an iterator, as its third argument.
std::unitialized_copy or std::copy would work, depending on whether the
destination is initialized (although that's not really an issue for
char values). memcpy also works fine, without having to decide whether
the target is initialized or whether that matters.

--
Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com) Author of "The
Standard C++ Library Extensions: a Tutorial and Reference
(www.petebecker.com/tr1book)