Question

The code below is passing the struct variable:

struct someStruct {
    unsigned int total;
};

int test(struct someStruct* state) {
    state->total = 4;
}

int main () {
    struct someStruct s;
    s.total = 5;
    test(&s);
    printf("\ns.total = %d\n", s.total);
}

(The source from Pass struct by reference in C
)

While programming in C++ may I pass this structure without &? I mean

test(s); // or should test(&s);

Will s be copied if I do that?

Answer 1

In C++ you can make the function take a reference as parameter:

int test(someStruct& state) {
    state.total = 4;
}

You can call the function like that:

someStruct s;
test(s);

No copy will be made. Inside the function, state will behave like it was s. Note that the struct keyword is only required when declaring the struct in C++. Also, in C++ your printing code should look like this:

std::cout << "s.total = " << s.total << std::endl;

You have to include iostream for that to work.