Question

#include<stdlib.h>



typedef struct HEAP_
{
      int size;

      void **tree;

      int (*compare)( const void *key1,const void *key2);
      void (*destroy) (void *data);
}Heap;

int main()
{
    Heap *H;
    void *temp;

     H=(Heap*)malloc(sizeof(Heap));

     if ((temp = (void **)realloc(H->tree, (5) * sizeof (void *))) == NULL) return -1;
     H->tree=temp;

     int a=0001;
     int b=0002;

    H->tree[0]=&a;
    H->tree[1]=&b;

    //*(int*)H->tree[0]=0001;
    //*(int*)H->tree[1]=0002;

    //printf("%d %d %d %d %d",H->tree[0],H->tree[1],H->tree,*(int*)H->tree[0],*(int*)H->tree[1],*(int*)*H->tree);
    //printf("%d %d %d ",*(int*)H->tree[0],*(int*)H->tree[1],*(int*)*H->tree);

我想弄清楚这些结果的种类，例如地址用完了，数字用完了 // printf（“％d％d”，（int ）H-> tree [0]，（int ）H-> tree [1]）;

    printf("%d %d  ", *(int*)H->tree[0] , *(int*)H->tree[1]);


    return 0;
}

当我构建并运行它时，编译器告诉我，最后一个无法打印，我该如何解决？似乎我误解了指针。

Answer 1

您已为该结构分配了内存：

H=(Heap*)malloc(sizeof(Heap));

，但是您没有为其成员树分配内存。您还需要这样做：

H->tree = malloc(required_size);

所以您的工作代码如下：

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

typedef struct HEAP_
{
      int size;
      void **tree;
      int (*compare)( const void *key1,const void *key2);
      void (*destroy) (void *data);
}Heap;

int main() {
        Heap *H; 
        void *temp;
        H=malloc(sizeof(Heap));
        H->tree=NULL;
        if((temp = malloc(5*sizeof(void *))) ==  NULL)
                 return -1; 
        H->tree=temp;
        int a;
        a=1;
        int b;
        b=4;
        H->tree[0]=&a;
        H->tree[1]=&b;
        printf(" %d\n ", *(int *)H->tree[0]);
        printf(" %d\n ", *(int *)H->tree[1]);
        return 0;
}

Answer 2

Here the answer :

您需要为堆分配内存，如下所示，

 H=(Heap*)malloc(sizeof(Heap));

您也为双指针分配了内存。

H-> tree = malloc（sizeof（int **） 2 / 指针数量* /）;

H-> tree [0] =（int *）malloc（sizeof（int））;

H-> tree [1] =（int *）malloc（sizeof（int））;

将值分配给tree [0]，如下所示，

    *((int*)H->tree[0]) = 25;

工作代码如下：

typedef struct HEAP_
{
      int size;

        void **tree;

       int (*compare)( const void *key1,const void *key2);
        void (*destroy) (void *data);
}Heap;

   int main()  
   {  
    Heap *H;  

      H=(Heap*)malloc(sizeof(Heap));  
      H->tree = malloc(sizeof(int**)*2);  
      H->tree[0]=(int*)malloc(sizeof(int));  
      H->tree[1]=(int*)malloc(sizeof(int));  
      *((int*)H->tree[0]) = 25;

      printf("%d",*((int*)H->tree[0]));


      return 0;
    }

在这种情况下如何使用双指针

2 个答案: