about return an array

[Janeson89]

OK. I get it that to return multiple variables from a function is a dead end. And to use global variables is simply too messy when the program grows bigger. And if I use pointers, well, god knows whether the memory space the functions created still exists when the "return" is performed. And so, I really have no idea how to pass an array back with a "return". Any one has a better idea?
Thanks very much for the help...

[roberts]

You could pass the array and array size in the parameters of the function call and get your changes back that way.

A real quick example:

#include <iostream>
#include <ctime>

using namespace std;

#define ARRAYSIZE 10

int change_array( int *, int );

int main( int arc, char *argv[] )
{
	int array[ARRAYSIZE];
	int recvresult;


	cout << "Array before function call" << endl;

	for( int i = 0; i < ARRAYSIZE; i++ )
		cout << array[i] << endl;

	recvresult = change_array( array, ARRAYSIZE );

	cout << endl;
	cout << "Array after funtion call" << endl;

	for( int i = 0; i < ARRAYSIZE; i++ )
		cout << array[i] << endl;

	cin.get();
}

int change_array( int *ar1, int ars )
{
	srand( time(NULL ));

	for( int i = 0; i < ars; i++ )
	{
		ar1[i] = rand();
	}

	return true;
}

[Cubbi]

I get it that to return multiple variables from a function is a dead end

map::insert, std::mismatch, and many other standard functions return two values each. But yes, with multiple values, it's better to return a container

I really have no idea how to pass an array back with a "return".

Why array? Return a vector

vector<int> some_function()
{
   vector<int> v;
   // do stuff that fills it up
    return v;
}

[therockon7throw]

create your own array class
or go to http://sourceforge.net/projects/ and search for some Matrix C++ Library have a look at their documentation first, than see which one is better has documented and is easy for you. Download it and learn from their codes and programming techniques.

[kbw]

Don't create you own class, use a standard container (like vector).

[therockon7throw]

You learn only if you create yours, you may have bugs, errors in your code, but you lear by doing, but not by using STL :-)

[Cubbi]

@therockon7throw would you recommend writing your own std::cout before learning how to use the one provided by the standard library? First learn how to use basic C++, then how to extend it.

[mik2718]

You can return an STL container from a function but if it is big then there will be a lot of copying going on.

Another option is to pass a non-const reference to the container into the function and then fill the the container in the function.

A third option is to use a reference counted object to avoid the deep copying going on. Either make this yourself or use a smart pointer such as boot::shared_ptr

[Peter87]

mik2718 wrote:

You can return an STL container from a function but if it is big then there will be a lot of copying going on.

Most compilers today will do RVO to avoid the copying. In C++11 if you return a local vector, it is guaranteed that there will be no copying of the elements.

[Janeson89]

I find using a structure useful for my case, it permit me passing multiple values of different types. Thanks, guys~

[viliml]

int* foo (int* array)
{
      return array;
      }

most simple array-returning function. I dont get why is that so difficoult!

[Peter87]

@viliml, How was a allocated? Do the caller need to delete the array?

[viliml]

int*foo (int* array)
{
      return array;
      }

int main()
{
      int a[3]={1, 2, 3};
      int* b=foo (a);
      std::cout<<b[0]<<" "<<b[1]<<" "<<b[2];
      return 0;
      }

1 2 3

Sorry, return a; was a mistake, I meant return array;