将无类型数组编译为C的有效方法是什么？

Question

I'm compiling code from a language that allows for untyped, dynamic arrays (such as JavaScript) to C. What is the best way to represent those arrays on it? Example:

var array = [1,2,"test",[1,2]];
array.push([5]);

Notice the lack of proper shape and size.

For the lack of proper shape, I've thought in boxing everything in a struct, that would contain a pointer to the actual objects. So I could have an array of that box. Would GCC be capable of unboxing that so I have no performance penalties, or should I look for an alternative solution?

For the lack of static size, I'm not sure what the best approach is.

Answer 1

This is generally what unions are for; at least, they're the most memory- and time-efficient solution. Make each entry of the array a struct with two members: an integer that marks the type of data, and a union containing all possible types you might store.

Example:

struct typed_elem {
    int type;
    union {
        int32_t i;
        double f;
        char *s;
        struct typed_elem *a;
    } value;
};

This would allow your array to contain integers, floating point (doubles), strings, or further arrays like itself. The type member would hold a code (you may prefer to use enum instead of int ) you make up to tell your program which member of the union is active.

Answer 2

You should either use ArrayBuffer (TypedArrays / ByteArrays) in Javascript to create structs that are static or transmit data via JSON between the two languages. In order to use dynamic structures in C, you will need to come up with some form of a header for each element that will give you a clue on how to parse the next few bits.

What I would suggest is to use Typed Arrays . That way you can have an identical struct in C and Javascript.