问“sizeof”对不完整类型的应用无效

EN

trie: trie.o main.o
    gcc trie.o main.o -o trie -std=c11 -g -Wall

trie.o: trie.c trie.h
    gcc -c trie.c -o trie.o -std=c11 -g -Wall

main.o: main.c trie.h
    gcc -c main.c -o main.o -std=c11 -g -Wall

clean:
    rm -f *.o trie

#ifndef TRIE_H
#define TRIE_H

struct node;
typedef struct node node;

//insert a word in a leaf
void insert(char* word, node* leaf);

#endif //TRIE_H

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "trie.h"

struct node {
  char* data;
  node* child[127];
};

void insert (char* word, node* leaf) {
  node* curr = leaf;
  for (size_t i = 0; i < strlen(word); i++) {//start from beginning of char to end
    if (curr == NULL) {
      curr = (node*)malloc(sizeof(node)); // if it's null, creating new node
      curr->data = "";
    }
    curr = curr->child[(int) word[i]];
  }
  curr->data = word; // set last node stored the word
}

#include <stdio.h>
#include <stdlib.h>

#include "trie.h"

int main() {
  node* x = (node*) malloc(sizeof(node));
  insert("hi", x);
  return 0;
}