取消引用指向不完整類型的指針（基數樹）

Question

我的結構定義遇到了很大的麻煩。我嘗試了幾種不同的方式來定義它們，但似乎無法擺脫錯誤。

我可能也有代碼的其他問題的財富，但我實際上無法通過運行我認爲的代碼找到它們而無法修復這些問題。這就是爲什麼我需要首先解決這個問題。

下面是完整的代碼：

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

typedef int bool; 
enum { false, true }; 

typedef struct radixNode { 
    bool active; 
    struct node * pnt; 
    struct node * l; 
    struct node * r; 
} node; 

void insert(node *root, char * B) { 

    // digit is zero so we go left 
    if (B[0] == 0) { 

     // left child doesn't exist, create it 
     if (root->l == NULL) { 

      root->l = malloc(sizeof(node)); 

      /* if the next index in the string does NOT contain a 1 or 0, 
      the current index is the last index and the node is activated */ 
      if (B[1] == 1 || B[1] == 0) 
       root->l->active = false; 
      else 
       root->l->active = true; 

      root->l->pnt = root; 
      root->l->l = NULL; 
      root->l->r = NULL; 
      insert(root->l,B++); // B++ removes the first digit of the string 
     } 

     // left child exists, traverse 
     else { 
      insert(root->l,B++); 
     } 
    } 

    // digit is one, go right 
    else { 

     // right child doesn't exist, create it 
     if (root->r == NULL) { 

      root->r = malloc(sizeof(node)); 

      /* if the next index in the string does NOT contain a 1 or 0, 
      the current index is the last index and the node is activated */ 
      if (B[1] == 1 || B[1] == 0) 
       root->r->active = false; 
      else 
       root->r->active = true; 

      root->r->pnt = root; 
      root->r->l = NULL; 
      root->r->r = NULL; 
      insert(root->r,B++); 
     } 

     // left child exists, traverse 
     else { 
      insert(root->r,B++); 
     } 
    } 
} 

node * printTreeMin(node *root) { 

    char * C[10]; 

    /* goes left until it can't, appends 0 to string 
    till it can't. if node is active, print the string */ 
    while (root->l != NULL) { 

     C[strlen(C)] = '0'; 

     if (root->active) 
      printf("&s\n",C); 

     root = root->l; 
    } 

    return root; 
} 

// prints the next smallest binary number in the tree, returns the node it printed 
node * printNextSmallest(node * root) { 

    char * C[10]; 

    // if right child exists, go there and find lowest node (after if same deal as printTreeMin()) 
    if (root->r != NULL) { 

     C[strlen(C)] = '1'; 
     if (root->active) 
      printf("&s\n",C); 

     root = root->r; 

     while (root->l != NULL) { 

      C[strlen(C)] = '0'; 
      if (root->active) 
       printf("&s\n",C); 

      root = root->l; 
     } 

     return root; 
    } 

    node * temp = root->pnt; 

    while (temp != NULL && root == temp->r) { 

     root = temp; 
     temp = temp->pnt; 
    } 

    return temp; 
} 

void printRadixTree(node *root) { 

    root = printTreeMin(root); 

    while (printNextSmallest(root) != NULL) 
     root = printNextSmallest(root); 
} 

void test() { 

    node * tree = malloc(sizeof(node)); 
    tree->l = NULL; 
    tree->r = NULL; 

    // a) 
    insert(tree,"101000"); 
    insert(tree,"10100"); 
    insert(tree,"10110"); 
    insert(tree,"101"); 
    insert(tree,"1111"); 

    // b) 
    printRadixTree(tree); 

} 

int main() { 
    test(); 
} 

這裏有錯誤，我得到：

|In function 'insert':| 
30|error: dereferencing pointer to incomplete type| 
32|error: dereferencing pointer to incomplete type| 
34|error: dereferencing pointer to incomplete type| 
35|error: dereferencing pointer to incomplete type| 
36|error: dereferencing pointer to incomplete type| 
37|warning: passing argument 1 of 'insert' from incompatible pointer type [enabled by default]| 
17|note: expected 'struct node *' but argument is of type 'struct node *'| 
42|warning: passing argument 1 of 'insert' from incompatible pointer type [enabled by default]| 
17|note: expected 'struct node *' but argument is of type 'struct node *'| 
57|error: dereferencing pointer to incomplete type| 
59|error: dereferencing pointer to incomplete type| 
61|error: dereferencing pointer to incomplete type| 
62|error: dereferencing pointer to incomplete type| 
63|error: dereferencing pointer to incomplete type| 
64|warning: passing argument 1 of 'insert' from incompatible pointer type [enabled by default]| 
17|note: expected 'struct node *' but argument is of type 'struct node *'| 
69|warning: passing argument 1 of 'insert' from incompatible pointer type [enabled by default]| 
17|note: expected 'struct node *' but argument is of type 'struct node *'| 

|In function 'printTreeMin':| 
82|warning: passing argument 1 of 'strlen' from incompatible pointer type [enabled by default]| 
49|note: expected 'const char *' but argument is of type 'char **'| 
82|warning: assignment makes pointer from integer without a cast [enabled by default]| 
87|warning: assignment from incompatible pointer type [enabled by default]| 

|In function 'printNextSmallest':| 
101|warning: passing argument 1 of 'strlen' from incompatible pointer type [enabled by default]| 
49|note: expected 'const char *' but argument is of type 'char **'| 
101|warning: assignment makes pointer from integer without a cast [enabled by default]| 
105|warning: assignment from incompatible pointer type [enabled by default]| 
109|warning: passing argument 1 of 'strlen' from incompatible pointer type [enabled by default]| 
49|note: expected 'const char *' but argument is of type 'char **'| 
109|warning: assignment makes pointer from integer without a cast [enabled by default]| 
113|warning: assignment from incompatible pointer type [enabled by default]| 
119|warning: initialization from incompatible pointer type [enabled by default]| 
121|warning: comparison of distinct pointer types lacks a cast [enabled by default]| 
124|warning: assignment from incompatible pointer type [enabled by default]| 

||=== Build failed: 10 error(s), 16 warning(s) (0 minute(s), 0 second(s)) ===| 

Answer 1

正如在評論中發現，你的問題是從你的結構定義：

typedef struct radixNode { 
    bool active; 
    struct node * pnt; 
    struct node * l; 
    struct node * r; 
} node; 

您在typedef結束之前調用struct node。只需struct node由struct radixNode。

對於你的第二個問題，這是因爲你的變量C是一個指針數組，而不是一個字符數組，並且你試圖將一行分配給一個char。如果你想創建一個十字節長的字符數組，只是把它定義是這樣的：

char C[10]; 

順便說一下，如果你想打印的printf同一個字符串，它與%s，不&s。