Can a function return more than one value?

Question

Can a function return more than one value directly (i.e., without returning in parameters taken by-reference)?

In case you want a language-agnostic overview, here's a question: http://stackoverflow.com/questions/1468375/how-do-you-return-two-values-from-a-single-method — P Shved, Apr 03 '10 at 16:52
You can return as an array or you can pass an array as a reference and store these values into that array. — pocoa, Apr 04 '10 at 02:19

score 24 · Answer 1 · answered Apr 04 '10 at 07:19

In the boost::tuple library, there's a function called tie that simplifies the process of getting information out of a returned tuple. If you had a function that returned a tuple of two doubles and wanted to load those into two local variables x and y, you could assign your function's return value to boost::tie(x, y).

Example:

#include <math.h>
#include <iostream>
#include <boost/tuple/tuple.hpp>

const double PI = 3.14159265;

boost::tuple<double, double> polar_to_rectangular(double radius, double angle)
{
    return boost::make_tuple(radius * cos(angle), radius * sin(angle));
}

int main()
{
    double x;
    double y;

    boost::tie(x, y) = polar_to_rectangular(4, (45 * PI) / 180);
    std::cout << "x == " << x << ", y == " << y << std::endl;

    return 0;
}

When I tried to use `boost::tuple`, it gave me error `fatal error: boost/tuple/tuple.hpp: No such file or directory`, it's not part of some [standard library](https://en.cppreference.com/w/cpp/header)? I am running my program on ubuntu16.04 with command `g++ -std=c++11 swap.cpp -o main`. if I don't use `boost::tuple`, my program runs fine! Any suggestions what I am doing wrong? — Anu, Jan 14 '19 at 22:24

score 15 · Answer 2 · edited Nov 18 '18 at 09:53

15

Yes - have your function return a struct. Or return the values via reference parameters.

struct A {
   int x, y;
   A(int x, int y) : x(x), y(y) {}
};

A myfun() {
   return A(0, 42);    // return  two values
}

or:

void myfun(int & a, int & b) {
   a = 0;
   b = 42;
}

edited Nov 18 '18 at 09:53

user2899298

3
1
3

answered Apr 03 '10 at 16:21

4

Though technically that's still one value in C – Nathan Fellman Apr 03 '10 at 16:22
Is this answering the question, "Can a function modify more than one value?" It can also modify globals if you want to be complete. – Hogan Apr 03 '10 at 16:25
but still only one value(its address) has been sent and we can access the whole object by copying it into another object. i want to know specifically whether we can assign two values simultaneously. – Ashish Yadav Apr 03 '10 at 16:31
@ashish No addresses involved. But to answer your second question, no you can't. – Apr 03 '10 at 16:35

rlbond · Accepted Answer · 2010-04-04T05:59:44.920

13

No, but you can return a pair or boost::tuple which can contain multiple values.

In addition, you can use references to return multiple values like this:

void MyFunction(int a, int b, int& sum, int& difference);

You would call this function like this:

int result_sum;
int result_difference;
MyFunction(1, 2, result_sum, result_difference);

As Hogan points out, technically this isn't returning multiple variables, however it is a good substitute.

edited Apr 04 '10 at 05:59

answered Apr 03 '10 at 16:22

rlbond

65,341
56
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9

Nit pick: "In addition, you can return multiple values like this:" should be "In addition, you can modify multiple values like this:". You can also modify globally scoped variables. – Hogan Apr 03 '10 at 16:26

Brian R. Bondy · Answer 4 · 2010-04-03T16:32:30.143

1

A function can return values in the specified ways:

Via return value of any type
Via a pointer
Via a reference
Via setting a global variable (highly not recommended)

If you need a self contained return value, you would typically wrap the types you need in a struct and return an object of that struct by value. If you want to avoid keeping a local copy you would pass in a reference parameter to be modified.

edited Apr 03 '10 at 16:32

answered Apr 03 '10 at 16:24

Brian R. Bondy

339,232
124
596
636

score 1 · Answer 5 · edited Jun 18 '11 at 10:27

1

#include<stdio.h>
#include<stdlib.h>
#include<string.h>

typedef struct
{
    int a;
    int b;
}Mystruct;

Mystruct myfun(); 

int main()
{
    char name[30];
    Mystruct ms2;
    ms2 = myfun();
    printf("val1: %d   val2: %d",ms2.a,ms2.b);
    return 0;
}

Mystruct myfun()
{
    int a,b;
    Mystruct ms;

    a = 10;
    b = 20;
    ms.a=a;
    ms.b=b;

    return(ms);
}

edited Jun 18 '11 at 10:27

Bo Persson

90,663
31
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203

answered Aug 28 '10 at 10:07

Saurabh

31
1

score 0 · Answer 6 · answered Aug 28 '10 at 09:58

0

use structure and return multiple value with different data type.

answered Aug 28 '10 at 09:58

Saurabh

31
1

score -4 · Answer 7 · edited Jun 18 '11 at 10:34

-4

main()
{
  int a=10,b=20;
  int *c;
  c=aa(a,b);
  printf("%d %d",*c,*c+1);
}

void aa(int a,int b)
{
   int c1[2];
   c1[0]=b+a;
   c1[1]=a-b;
   return(c1);
}

here, the address of c1 will be return. so it will store in main c cariable. we can retrive both variable via pointer,

edited Jun 18 '11 at 10:34

Bo Persson

90,663
31
146
203

answered Aug 18 '10 at 07:58

karthi madheswaran

1

2

Leads to undefined behavior. `c1`'s lifetime ends when `aa` is left, so `c` is left pointing at a dead object. Accessing it leads to undefined behavior. – GManNickG Aug 18 '10 at 08:07

Can a function return more than one value?

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