"derefeerncing pointer to incomplete type" - 尝试在动物猜谜游戏C中制作树节点

Question

main：

int main(int argc, char *argv[])
{   
    printf("Please think of an animal. I will try to find out what it is by asking you some yes/no questions.");
    struct treenode *root = mkTreeNode("Is it a reptile?n", NULL, NULL);
    struct treenode *selectedNode = root;
    root->left = mkTreeNode("Does it have legs?n", NULL, NULL);
    root->right = mkTreeNode("Is it a mammal?n", NULL, NULL);
    root->left->left = mkTreeNode("Crocodile", NULL, NULL);
    root->right->left = mkTreeNode("Elephnt", NULL, NULL);

mkTreeNode：

struct treenode {
 char *animal;
 struct treenode *left;
 struct treenode *right;
};
struct treenode *mkTreeNode(char *str, struct treenode *lChild, struct treenode *rChild) {
struct treenode *node = malloc(sizeof(struct treenode));
  node -> left = lChild;
  node -> right = rChild;
  node -> animal = str;
  return node;
}

我在主线的第 6 行出现错误

root->left = mkTreeNode("Does it have legs?n", NULL, NULL);

"取消引用指向不完整类型的指针";有什么想法吗？我需要另一个malloc什么的吗？

Answer 1

如果显示的代码位于不同的文件中，则不清楚struct声明是否从包含main()的 C 文件中可见。如果不是，则在尝试访问结构的字段时会收到该错误。

更新 你说它都在一个文件中，尽管它看起来不像那样。在这种情况下，请注意顺序很重要，struct声明必须出现在（上）main()之前。

基本上，这应该有效：

#include <stdio.h>
#include <stdlib.h>
struct treenode {
 char *animal;
 struct treenode *left;
 struct treenode *right;
};
struct treenode *mkTreeNode(char *str, struct treenode *lChild, struct treenode *rChild)
{
  struct treenode *node = malloc(sizeof *node);
  node->left = lChild;
  node->right = rChild;
  node->animal = str;
  return node;
}
int main(int argc, char *argv[])
{   
  printf("Please think of an animal. I will try to find out what it is by asking you some yes/no questions.");
  struct treenode *root = mkTreeNode("Is it a reptile?n", NULL, NULL);
  struct treenode *selectedNode = root;
  root->left = mkTreeNode("Does it have legs?n", NULL, NULL);
  root->right = mkTreeNode("Is it a mammal?n", NULL, NULL);
  root->left->left = mkTreeNode("Crocodile", NULL, NULL);
  root->right->left = mkTreeNode("Elephant", NULL, NULL);
  return 0;
}