Find an array element in compile time

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First of all, sorry if this question (or some similar one) has been previously asked, I've searched for it but I've not found a valid solution in plain C. Also, sorry for the extension.

I've got an array like this:

struct item{
    int id;
    char *str;
};

const struct item items[] = {
    {4, "FIRST_ELEMENT"},
    {6, "SECOND ELEMENT"},
    {0, NULL}
}

How I could know, in compile time, what position of the array hold the element with id number 4? I could do this in C++ with templates, but in plain C I've no idea how to achieve it.

Please note that the ids of the elements are non-consecutives: I can have all the elements with ids 1-200 and them the ids 4000-4500 filled. I cannot choose the ids.

-- long version --

The elements I manage have inter-dependence. For example, if I process an element with id 10, I've got to process the element with id 15 and 20, all in a predefined way.

At the moment, I've got an struct like this:

#define MAX_NUMS_OF_CHILDS 5

struct item{
    int id;
    char *str;
    int childs_id[MAX_NUM_OF_CHILDS];
    struct item *child[MAX_NUM_OF_CHILDS];
};

const struct item items[] = {
    {4, "FIRST_ELEMENT"},
    {6, "SECOND_ELEMENT"},
    {10, "FATHER ELEMENT", {15, 20}}
    {15, "SON ELEMENT 1"},
    {120, "SON ELEMENT 2"},

    {0, NULL}
}

And, at startup time, a function fills the item->child with the information of item->child_id. But I'm sure there is a more elegant way to do this, omitting the child_id field at all.

Thanks in advance!

asked 1 min ago

user3473433

1