Can i assign in 2 variables at the same time in C++?

Question

int DFS(a, b,c,d)
{
    first=a+b;
    second=c+d;
    return(first,second);
}

solution, cost_limit = DFS(a, b,c,d);

can I do something like this ? and how?

It's very unclear what you're asking here. I would suggest you explain what you mean by assign, and what you mean by a variable. — Samuel Harmer, Jan 12 '12 at 10:55

score 29 · Accepted Answer · answered Jan 12 '12 at 10:37

29

In C++11 you can use the tuple types and tie for that.

#include <tuple>

std::tuple<int, int> DFS (int a, int b, int c, int d)
{
    return std::make_tuple(a + b, c + d);
}

...

int solution, cost_limit;
std::tie(solution, cost_limit) = DFS(a, b, c, d);

answered Jan 12 '12 at 10:37

filmor

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If C++11 is not an option, the [Boost Tuple library](http://www.boost.org/doc/libs/release/libs/tuple/doc/tuple_users_guide.html) provides these features. – Luc Touraille Jan 12 '12 at 10:40
If C++11 is not an option, you still can use C++03's `std::pair` – Antonio Pérez Jan 12 '12 at 10:42
@Antionio: but there's no `tie` in C++03, so it comes out looking pretty ugly: `std::pair result = DFS(a,b,c,d); solution = result.first; cost_limit = result.second;`. – Steve Jessop Jan 12 '12 at 10:44
You could use TR1, I think that one also features the tuple library (with `tie`) – filmor Jan 12 '12 at 11:07
in C++17, use structured declarations with pair – madhur4127 Mar 23 '20 at 17:49

ztyreg · Answer 2 · 2020-12-01T23:52:49.537

12

With C++17, you can unpack a pair or a tuple

auto[i, j] = pair<int, int>{1, 2};
cout << i << j << endl; //prints 12
auto[l, m, n] = tuple<int, int, int>{1, 2, 3};
cout << l << m << n << endl; //prints 123

edited Dec 01 '20 at 23:52

answered Sep 09 '20 at 03:41

ztyreg

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And you don't need the `` anymore BTW: https://stackoverflow.com/questions/9270563/what-is-the-purpose-of-stdmake-pair-vs-the-constructor-of-stdpair/41521422#41521422 – Ciro Santilli OurBigBook.com Nov 11 '20 at 11:11
This is bundled with declaration. The question is how to assign to existing variable. – Audrius Meškauskas Dec 09 '21 at 09:32

score 1 · Answer 3 · edited Jun 26 '15 at 17:21

1

You can do this two ways:

Create a struct with two values and return it:

struct result
{
    int first;
    int second;
};

struct result DFS(a, b, c, d)
{            
    // code
}

Have out parameters:

void DFS(a, b, c, d, int& first, int& second)
{
    // assigning first and second will be visible outside
}

call with:

DFS(a, b, c, d, first, second);

edited Jun 26 '15 at 17:21

eddi

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answered Jan 12 '12 at 10:31

Tudor

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This is clearly not what the OP is asking for. He's asking for returning two separate values into two separate variables. – Szabolcs Jan 12 '12 at 10:32
1

This is not what he asked for. He wants the pythonic way, meaning `solution = first; cost_limit = second;` – filmor Jan 12 '12 at 10:33

score 0 · Answer 4 · edited Jan 12 '12 at 10:46

One thing you should be know is that if a,b,c,d are not base types, but instances of a class you defined, let's say Foo, and you overload the = operator of the class, you must ensure the fact that the operator will return a reference to the object which is assigned, or else you will not be able to chain assignments ( solution = cost_limit = DFS(..) will only assign to cost_limit). The = operator should look like this:

Foo& Foo::operator =(const Foo& other)
    {
       //do stuff
       return other;
    }

score 0 · Answer 5 · answered Jan 12 '12 at 10:47

If C++11 is not possible, it's possible to use references.

By passing a reference to variables in parameters.

int DFS(int a, int b, int c, int d, int &cost_limit)
{
    cost_limit = c + d;
    return a + b;
}

int solution, cost_limit;

solution = DFS(a, b, c, d, cost_limit);

Can i assign in 2 variables at the same time in C++?

5 Answers5