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Maxium number of values returnable by single fucntion ?

Posted on 2007-03-19
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Last Modified: 2010-04-01
How many values can a function return ?

I have a function which accepts several pointers. It's return type is int*

If I had the following would both be returned ?

      (*value01)++;
      return value01;
      (*value02)++;
      return value02;

Or do I even need to specify a return type because the pointers would be changed whether I returned them or not ?

Thanks.
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Question by:andyw27
8 Comments
 
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Infinity08 earned 500 total points
ID: 18751344
>> If I had the following would both be returned ?

No, you can only return one parameter. So, this code :

      (*value01)++;
      return value01;    //  <---- value01 will be returned
      (*value02)++;       // <----- this will never be executed
      return value02;    // <----- this will never be executed

There are several ways to return multiple values. Here are a few :

1) pass by pointer :

        void fun(int *value01, int *value02) {
            (*value01)++;
            (*value02)++;
            return;
        }

    call it like this :

         int val1 = 1;
         int val2 = 2;
         fun(&val1, &val2);
         // val1 now has value 2
         // val2 now has value 3

2) pass by reference :

        void fun(int &value01, int &value02) {
            value01++;
            value02++;
            return;
        }

    call it like this :

         int val1 = 1;
         int val2 = 2;
         fun(val1, val2);
         // val1 now has value 2
         // val2 now has value 3

3) return a struct :

        struct retvals {
            int val1;
            int val2;
        }

        retvals fun(retvals vals) {
            (vals.val1)++;
            (vals.val2)++;
            return vals;
        }

    call it like this :

         retvals vals = { 1, 2 };
         vals = fun(vals);
         // vals.val1 now has value 2
         // vals.val2 now has value 3
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Author Comment

by:andyw27
ID: 18751403

Thanks thats a great answer.
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LVL 16

Expert Comment

by:AlexNek
ID: 18751715
As it is C++ I would suggest to create a class like
class CCounters
{
public:
   CCounters(): m_Value1(0), m_Value2(0) {}
    void IncValue1() {m_Value1++;}
    void IncValue2() {m_Value2++};
    void IncAll() {IncValue1(); IncValue2();}
private:
   int  m_Value1;
   int M_Value2;
}
...
CCounters Counters;
..
func(Counters);

...
void func(CCounter& rCounters)
{
....
  rCounters.IncAll();
}
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Expert Comment

by:MacroLand
ID: 18751868
or another function could be like;

int* returnSomething(int* p1,int* p2)
{
  int* ret=new int[5];
  p1++;
  p2++;

  for (int i=0;i<5;i++)
     *(ret+i)=i;

  return ret;

}

Here both p1 and p2 is modified and you also get five different value, or as much as you can

To use it;

int main()
{
   x=5;y=7;
   int* pf=returnSomething(&x,&y);

  //now x and y are both incremented
  for (int i=0;i<5;i++)
    std::cout<<*(pf+i)<<std::endl;

return
}

Regards,
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LVL 16

Expert Comment

by:AlexNek
ID: 18752203
In addition you have the memory leak.
I'm sorry, but the last suggestion I would be never recommended because it is a "dirty" solution.
I think the answer coud be:
The function can return only one value as return. This value can be a value, a pointer or a reference.

So we can return the complex object and this object can hold as many values as we need.
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LVL 4

Expert Comment

by:MacroLand
ID: 18754313
>>In addition you have the memory leak.

int main()
{
   x=5;y=7;
   int* pf=returnSomething(&x,&y);

  //now x and y are both incremented
  for (int i=0;i<5;i++)
    std::cout<<*(pf+i)<<std::endl;

    delete pf; //delete the memory pointed by pf

    return 0;
}

Would you still have the memory leaks?
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Expert Comment

by:AlexNek
ID: 18755182
In this case not any more but in real project it is very easy to forget it.
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Expert Comment

by:itsmeandnobodyelse
ID: 18755310
>>>  but in real project it is very easy to forget it.
Yes, normally you should delete a pointer where you created it. Only *create* functions where the only purpose is to create a new pointer are an exception from above rule. In a class you should store newly created pointers (if there is a need for pointers at all) in a data member and delete in the destructor.

Regards, Alex
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