C++ Using struct


Example

A struct can be used to bundle multiple return values:

C++11
struct foo_return_type {
    int add;
    int sub;
    int mul;
    int div;
};

foo_return_type foo(int a, int b) {
    return {a + b, a - b, a * b, a / b};
}

auto calc = foo(5, 12);
C++11

Instead of assignment to individual fields, a constructor can be used to simplify the constructing of returned values:

struct foo_return_type {
    int add;
    int sub;
    int mul;
    int div;
    foo_return_type(int add, int sub, int mul, int div)
    : add(add), sub(sub), mul(mul), div(div) {}
};

foo_return_type foo(int a, int b) {
     return foo_return_type(a + b, a - b, a * b, a / b);
}

foo_return_type calc = foo(5, 12);

The individual results returned by the function foo() can be retrieved by accessing the member variables of the struct calc:

std::cout << calc.add << ' ' << calc.sub << ' ' << calc.mul << ' ' << calc.div << '\n';

Output:

17 -7 60 0

Note: When using a struct, the returned values are grouped together in a single object and accessible using meaningful names. This also helps to reduce the number of extraneous variables created in the scope of the returned values.

C++17

In order to unpack a struct returned from a function, structured bindings can be used. This places the out-parameters on an even footing with the in-parameters:

int a=5, b=12;
auto[add, sub, mul, div] = foo(a, b);
std::cout << add << ' ' << sub << ' ' << mul << ' ' << div << '\n';

The output of this code is identical to that above. The struct is still used to return the values from the function. This permits you do deal with the fields individually.