Question

在结构中的数组内的结构中访问（使用指针）变量的正确方法是什么？

我想用function()的指针到达position2D中的变量x和y？请注意，我遍历函数（）中的节点（和点），并希望编写如下内容：

draw_point(p->vertices[i]->x, p->vertices[i]->y);

但这似乎不起作用。

typedef struct Position2D{
  uint8_t x;
  uint8_t y;
} position2D;

typedef struct Node{
  int num;
  position2D vertices[4];
  struct Node *next;
} node;

/* initialisation: */

node *next1 = NULL; //should be empty
node node1 = {1, {{0,0}, {5,0}, {5,5}, {0,5}}, &next1};
node *next0 = &node1;
node node0 = {0, {{0,10}, {10,10}, {10,15}, {0,15}}, &next0};
node *start = &node0;

/*traverse all nodes and their inner vertices arrays: */
void function(void){
node *p;
for(p = start; p != NULL; p = p->next){
  int i;
  for (i=0; i<4; i++){ //traverse their four points
    //How to get to the x and y at this line?
  }
}

Answer 1

vertices是一个普通的结构变量，而不是 struct pointer 类型。在访问x和y时，请使用点.运算符代替->运算符

替换以下声明

draw_point(p->vertices[i]->x, p->vertices[i]->y);

与

 draw_point(p->vertices[i].x, p->vertices[i].y);

编辑：分配next字段时代码中的另一个问题。

node node1 = {1, {{0,0}, {5,0}, {5,5}, {0,5}}, &next1};

应该是

node node1 = {1, {{0,0}, {5,0}, {5,5}, {0,5}}, (struct Node*)next1};

这是工作代码

#include<stdio.h>
typedef struct Position2D{
        int x;
        int y;
} position2D;

typedef struct Node{
        int num;
        position2D vertices[4];
        struct Node *next;
} node;
/*traverse all nodes and their inner vertices arrays: */
void function(void){
/* initialisation: */
        node *next1 = NULL;
        node node1 = {1, {{0,0}, {5,0}, {5,5}, {0,5}}, (struct Node*)next1};
        node *next0 = &node1;
        node node0 = {0, {{0,10}, {10,10}, {10,15}, {0,15}}, (struct Node*)next0};
        node *start = &node0;
        node *p = NULL ;
        int i=0;
        for(p=start;p!=NULL;p=p->next) {
                for (i=0; i<4; i++){ //traverse their four points
                        printf("%d %d \n",p->vertices[i].x, p->vertices[i].y);
                }
        }

}
int main() {
        function();
        return 0;
}

访问结构中数组内的结构

1 个答案: