Cannot assign an array to another

Question

I tried through different ways to copy an array pointer to another one, without any success. Here are my attempts, with the associated error message.

typedef long int coordinate;
typedef coordinate coordinates[3];

void test(coordinates coord) {
    coordinates coord2 = coord; // error: invalid initializer
    coordinates coord3;
    coord3 = coord; // error: incompatible types when assigning to type ‘coordinates’ from type ‘long int *’
    coord3 = (coordinates) coord; // error: cast specifies array type
    coord3 = (coordinate[]) coord; // error: cast specifies array type
    coord3 = (long int*) coord; // error: incompatible types when assigning to type ‘coordinates’ from type ‘long int *’
}

I know I could use typedef coordinate* coordinates; instead, but it does not look very explicit to me.

Answer 1

You cannot assign arrays in C. Use memcpy to copy an array into another.

coordinates coord2;

memcpy(coord2, coord, sizeof coord2);

Answer 2

When arrays are passed by value, they decay to pointers. The common trick to work around that is wrapping your fixed-size array in a struct, like this:

struct X {
    int val[5];
};

struct X a = {{1,2,3,4,5}};
struct X b;
b = a;
for(i=0;i!=5;i++)
    printf("%d\n",b.val[i]);

Now you can pass your wrapped arrays by value to functions, assign them, and so on.