Handling functions with more than one output parameters

Question

How do we handle more than one output parameters in C++.I am beginner in C++ and currently i am trying to write a function A which calls another function B of some other class,Function B consists of 6 parameters in total ,of which three are input parameters and the rest three are output parameters.How can i access all the three output parameters within my function A?I tried to do it in the following way...Can anyone help me to correct my code if i have gone wrong..?Please do help me friends..

class A ::functionA()
   {
      int in_a=1;
      string in_b= "name";
      int in_c=3; 
      int ot_a=0;
      int ot_b=0;
      string ot_s1="" 

      ClassB *classB();
      classB = classB.functionB(in_a,in_b,in_c,ot_a,ot_b,ot_s1); //is this way correct?
      ot_a= ? ;
      ot_b=? ;
      ot_s1=?
    }

can i use something like ot_a=classB.ot_a ?Please help me...

What happened when you tried this? Did it work, or did it give you an error message? — Tim
– Tim, Commented Apr 14, 2011 at 6:32
please show the signature for B::functionB, or is what you are wondering about how to write functionB? — Mat
– Mat, Commented Apr 14, 2011 at 6:32

Naveen · Accepted Answer · 2011-04-14 06:33:59Z

2

You have got the basic syntax of C++ wrong. ClassB *classB(); does not create any object, it declares a function prototype of function classB which returns ClassB*. To create a object you should do ClassB b; and then use b as you have done. The output variables will be correctly filled up by the function if it is taking its parameter by reference.

answered Apr 14, 2011 at 6:33

Naveen

73.8k47 gold badges182 silver badges237 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Xeo · Accepted Answer · 2011-04-14 06:35:26Z

2

For multiple return values, you got generally two choices:

return a struct containing your return values
pass the return values in per reference.

Both examples demonstrated:

// first approach, struct return
struct myReturns{
  int int_return;
  float float_return;
};

myReturns MyFunc(int param1, char* param2, ...){
  // do some stuff with the parameters
  myReturns ret;
  ret.int_return = 42;
  ret.float_return = 13.37f;
  return ret;
}

// calling it:
myReturns ret = MyFunc(/*pass your parameters here*/);
int i = ret.int_return;
float f = ret.float_return;

// second approach, out parameters
void MyFunc(int inParam1, char* inParam2, int& outInt, float& outFloat){
  // do some stuff with the parameters
  outInt = 42;
  outFloat = 13.37f;
}

// calling it:
int i;
float f;
MyFunc(/*your parameters here*/,i,f);
// i and f are now changed with the return values

answered Apr 14, 2011 at 6:35

Xeo

132k55 gold badges299 silver badges406 bronze badges

1 Comment

Xeo Over a year ago

@Victor: I excluded pointer since the OP doesn't seem to be very experienced in C++. :) And shoo, globals!

Jonathan Merlet · Accepted Answer · 2011-04-14 07:10:42Z

As mentionned in Xeo's answer, you can use return structures or references. There is another possibility, to use pointers. Pointers allows you to do one thing : if the function you call can be used to compute multiple informations, but you don't want all of them, you can pass NULL as the value of the pointer so that the function knows it doesn't need to fill these informations.

Of course, the function you call needs to be designed that way, it's not automatic.

void f()  
{   
    type1* p1 = new type1();  
    type2* p2 = NULL
    g(p1, p2);
}

void g(type1* param1, type2* param2)  
{
    //Do some computation here
    if (param1 != NULL)
    {
        //Do something here to fill param1
    }
    if (param2 != NULL)
    {
        //Do something here to fill param2
    }
}

But as a general rule, it's better to use references when you can, and pointers when tou have to. If the function doesn't handle the case when a pointer passed to it is NULL, you will end with a crash. References can't be NULL, so they avoid this problem.

Dr McKay · Accepted Answer · 2011-04-14 06:32:18Z

0

Answer is: references.

answered Apr 14, 2011 at 6:32

Dr McKay

2,5582 gold badges21 silver badges26 bronze badges

Comments

Mahesh · Accepted Answer · 2011-04-14 06:34:25Z

0

ClassB *classB();
classB = classB.functionB(in_a,in_b,in_c,ot_a,ot_b,ot_s1);

By looking . operator after classB, I assume that you are thinking classB is an object. No, it is not.

ClassB *classB();

The above statement says - classB() is a function that takes no parameters and return type is a reference to ClassB.

answered Apr 14, 2011 at 6:34

Mahesh

34.7k23 gold badges93 silver badges116 bronze badges

4 Comments

Mahesh Over a year ago

@Als - I didn't mention anything on those lines in my post.

Mahesh Over a year ago

@Als - No where I have given my code. It is just the OP's code in the question and I am explaining what it is actually meant.

Mahesh Over a year ago

@Als - What more can I say to the OP than what he/she is creating is not an object. Any how will consider your suggestion here after. Thanks.

Alok Save Over a year ago

My bad seems I have been pre occupied or i misread someonelses response as yours...Apologies..Keep up the good work.

styken · Accepted Answer · 2011-04-14 06:37:36Z

0

If you can change functionB() then use pointers as parameters. This way you can change the value inside functionB() and they will be changed directly in functionA().

answered Apr 14, 2011 at 6:37

styken

746 bronze badges

Collectives™ on Stack Overflow

Handling functions with more than one output parameters

6 Answers 6

Comments

1 Comment

Comments

Comments

4 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

6 Answers 6

Comments

1 Comment

Comments

Comments

4 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related