Question

I’m trying to convert some code from Javascript to c. The function creates an array (which always has a fixed number of items) and then returns the array. I’ve learned that in c it’s not straightforward to return an array, so I’d like to return this as a struct instead. My c is not all that great, so I’d like to check that returning a struct is the right thing to do in this situation, and that I’m doing it the right way. Thanks.

typedef struct {
    double x;
    double y;
    double z;
} Xyz;

Xyz xyzPlusOne(Xyz addOne) { 

    Xyz xyz;
    xyz.x = addOne.x + 1;
    xyz.y = addOne.y + 1;
    xyz.z = addOne.z + 1;

    return xyz;
}

Answer 1

It’s perfectly good and correct C, but passing the structure by value may not be a good idea for larger structures or if you intend to change the structure in the caller:

Xyz s;
s = XyzPlusOne( s );

in which case you would be better off passing the structure as a pointer and simply saying:

Xyz s;
XyzPlusOne( & s );

On the other hand, if you want something like this:

Xyz s1, s2;
...,
s2 = XyzPlusOne( s1 );

then returning a value makes sense.