将 void 转换为具有相同格式的结构

Question

I have three structs with almost the same exact format.

struct name_basics {
    char *nconst;
    char *primaryName;
};

struct title_basics {
    char *tconst;
    char *primaryTitle;
};

And one more, but you get the point. Basically I need a function for each struct, whereas I would like to shorten it down to one.

struct nameNode *newNameNode(struct name_basics data) {
    struct nameNode *node = malloc(sizeof(struct nameNode));
    node->data = data;
    node->left = NULL;
    node->right = NULL;
    return node;
}

struct titleNode *newTitleNode(struct title_basics data) {
    struct titleNode *node = malloc(sizeof(struct titleNode));
    node->data = data;
    node->left = NULL;
    node->right = NULL;
    return node;
}

Is there any way to pass them as void, cast them to a sort of abstract struct, and use their data?

Answer 1

Unfortunately, there is no nice way of doing polymorphism in C. Whatever method you choose, it will at best be acceptable. In your case, since the structs looks exactly the same, I would consider reducing the number of structs to one and rename it to something generic.

But if you don't want to do that, a pretty generic way to do polymorphism is to use a union inside a struct. Whether it's good or bad is up to you. I would not use it.

struct myStruct {
    enum {name, title} type;
    union {
        struct name_basics a;
        struct title_basics b;
    } data;
};

void *newNode(struct myStruct data) {
    struct nameNode *nn;
    struct titleNode *tn;
    void *ret;
    switch(data.type) {
    case name:
        nn = malloc(sizeof(struct name_basics));
        nn->data = data.data.a;
        nn->left = nn->right = NULL;
        ret = (void*)nn;
        break;
    case title:
        tn = malloc(sizeof(struct title_basics));
        tn->data = data.data.b;
        tn->left = tn->right = NULL;
        ret = (void*)tn;
        break;
    }
    return ret;
}

Some of this could be simplified in your case because the structs are so similar, but this is a generic way.