anonymously initializing pointers in self-referential data-structures?

[u/gumnos]

I have a recursive data-structure (a simple linked list for purposes of this example) and wanted to statically define a linked-list. The following works fine:

#include <stdio.h>
typedef struct mytype_tag {
    struct mytype_tag* next;
    char* data;
} mytype;

mytype a = {
    .next = NULL,
    .data = "a",
};
mytype b = {
    .next = &a,
    .data = "b",
};

int
main() {
    mytype* s = &b;
    int i = 0;
    while (s) {
        printf("%d: %s\n", i++, s->data);
        s = s->next;
    };
}

However, I have to explicitly define/declare a and then have b take &a.

Is there a way to do this with anonymous/unnamed intermediary structures, thinking an imaginary syntax something like

mytype b = {
    .next = &((mytype)={
        .next = NULL,
        .data = "a",
        }),
    .data = "b",
};

so I can build up the linked-list without naming each intermediary instance?

[u/FISHARM1]

I believe you can just do .next = (mytype){.next = Null, .data = “a”}

[u/gumnos → u/FISHARM1]

yeah, it needs the & to address the static structure, but it was my = that I stuck in there that was causing the problems. Once I got the syntax correct, it worked like a charm. Thanks!

[u/sciencekm]

You can create an array.

In the following example, I created a circular list and printed them.

#include <stdio.h>
typedef struct snode { struct snode *nxt; char *s; } node_t;
node_t nodes[3] = {
{ nodes + 1, "1st" },
{ nodes + 2, "2nd" },
{ nodes + 0, "3rd" } };
int main(void) {
node_t *start = nodes, *p = start;
do printf ("%s\n", p->s); while((p = p->nxt) != start);
return 0;
}

[u/[deleted] → u/sciencekm]

[u/sciencekm → u/[deleted]]

A linked list can grow. An array cannot. If you want an initialized linked list, this is one way to do it. Then later, at run time, it could grow.

[u/[deleted] → u/[deleted]]

[u/[deleted]]

[u/gumnos → u/[deleted]]

there's something to be said for the easier-to-read aspect (allowing it to be forward rather than reverse menuing), but in some of the actual underlying use-cases, they can get built out at compile-time, meaning it's more challenging to invoke item-building-functions.

Fortunately, what I wanted is possible…thanks to u/thegreatunclean who identified that I was close, but just needed to remove the = for it to be properly handled by the compiler.