A C struct cannot directly contain a member of its type, as it would create an infinite size requirement for that struct. When you define a struct, each member inside must have a definite size so the compiler can allocate memory. If a struct were allowed to contain a member of its type, the compiler would try to allocate space for a struct within itself, which would lead to an infinite memory requirement.

#include <stdio.h>

typedef struct Node {

int x;

struct Node next;

} Node;

int main() {

printf("%zu\n", sizeof(Node));

return 0;

}

Running the above code will result in an error. For a straightforward reason, what is the size of the struct, and how can we calculate it? The compiler needs to know the size of identifiers so that when the compiled program is loaded in memory, enough space is allocated for the local variables on the stack.

ERROR!

/tmp/kB4k6cM4tf.c:6:17: error: field 'next' has incomplete type

6 | struct Node next;

| ^~~~

Does this mean a struct cannot hold a member of a struct type? Absolutely not. If the next member was from a different structure, the program would run efficiently; we could store members of other structures in our structure even without using pointers.

#include <stdio.h>

struct Foo {

int y;

};

typedef struct Node {

int x;

struct Foo next;

} Node;

int main() {

printf("%zu\n", sizeof(Node));

return 0;

}

Output:

8

However, storing a member that is a pointer to the same struct since we/compiler know the size of a pointer; all pointers are size 8.