Tuesday, June 07, 2005

C++ reference to an array

A number of years ago I remember learning how to pass a reference to an array of fixed size to a function in C++. The C++ Primer by Stan Lippman and Josee Lajoie discuss how to do this in section 7.3 (Functions - Argument Passing). It looks like this:

void foo(int (&refArr)[10])
{
size_t size = sizeof(refArr); // returns 10*sizeof(int)
}


Today Jonathan asked how to return a reference to an array of fixed size. I took a quick look at the spec and saw that returning a reference to an array is allowed, but I couldn't find how.

Well, it turns out that is looks like this:

const int (&getArray() const)[10]
{
return array_;
}


Fun!

15 comments:

Anonymous said...

Total fun!! :++)

Marina said...

hahaha

i just.. :++) while(TRUE)


ps. thanx for this post, i was looking actually for the reference to array as a parameter

Anonymous said...

Awesome, I was looking for this too. Make me question the code I'm writing ;)

Carl said...

Thanks for this. Say I have a reference to an nxn matrix. Is it possible to create a reference to an matrix (n/2)x(n/2) from it? I'm thinking of using this technique to construct hadamard matrices

Kevin Heifner said...

No. The array is contiguous in memory and therefore the (n/2)x(n/2) array would be slices.

GiM said...

Hi there, thanks for this explanation!

Saurav Deb Purkayastha said...

Thanks a lot for the post. I had been stuck at a program in which I was trying to reference an array. Your method worked. Now my program is done. Again thanks a lot!!!!!!!!!!!!!!

manuell said...

Many thanks to you, and to Google!

SEO Freelance said...

Whoa! Thanks for this. You simply enlighten me about references to array. I can now answer my assignment in school. Keep it up.

a1 said...

Thanks for this useful knowledge.

Gabriel Frâncu said...

http://www.unixwiz.net/techtips/reading-cdecl.html

to understand how to read that

Lei Yi said...

hi, where can I find the standard's description to "reference to fixed-size array" and "the syntax of return a array reference"? thanks.

Lei Yi said...
This comment has been removed by the author.
Kevin Heifner said...

The syntax for a reference to an array can be found in the standard at 8.5.3 References.

ChriSopht said...

You can slightly improve the syntax by a typedef:

struct Test {
  typedef int Array10[10];
  Array10 array;
  const Array10& getArray() const { return array;}
};