c指向结构问题的指针 [英] c pointer to struct issue

问题描述

以下代码在倒数第二条语句中的箭头处给我一个错误.我不知道为什么会这样.有人可以告诉我为什么吗?

The following code is giving me an error at the arrow in the second to last statement. I have no idea why this is . Could someone please tell me why?

我什至不知道从哪里开始.我以为是正确的，但是有一些问题.

I have no idea where to even begin. I thought it is correct but there is some issue.

      /* 
 * File:   newmain.c
 * Author: user1
 *
 * Created on May 26, 2015, 4:30 PM
 */

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
/*
 * 
 */


#ifndef KEYTYPE
#define KEYTYPE      char *
#endif

#ifndef VALUETYPE
#define VALUETYPE     double
#endif

#ifndef TYPE
#define TYPE struct association
//# define TYPE int
#endif

struct association
{

    KEYTYPE key;
    VALUETYPE value;

};

struct DynArr
{
    TYPE *data;     /* pointer to the data array */
        //struct association *data;
    int size;       /* Number of elements in the array */
    int capacity;   /* capacity ofthe array */
};


int main(int argc, char** argv) {

    struct DynArr *da;
    da = malloc(sizeof(struct DynArr));


    assert(da!= 0);
    da->capacity = 2;
    da->data = malloc(sizeof(TYPE) * da->capacity);
    assert(da->data != 0);
    da->size = 0;


    if(da->data[0]->key == 2) //test.c:58:10: error: invalid type argument of ‘->’ (have ‘struct DynArr’)    <<<<<<<<<<<<<<<<<<

    return (EXIT_SUCCESS);
}

推荐答案

您使用了错误的运算符，您的struct DynArr实例不是指针，因此必须使用.运算符.

You are using the wrong operator, your instance of struct DynArr is not a pointer, hence you must use the . operator.

struct DynArr da;
/* This is also wrong because `capacity' has not been initialized yet! */
assert(da.capacity > 0); 
      /* ^ it's not a poitner */

，其他所有情况都相同.

and in all the other cases the same.

当实例是struct的Poitner时，例如

When the instance is a poitner of struct, like

struct DynArr  da;
struct DynArr *pda;

pda = &da;
pda->capacity = 0;
 /* ^ it's correct here */

编辑:

您编辑完问题后，我可以看到问题了

After you edited your question I can see the problem

if(da->data[0]->key == 2)

da->data的类型为TYPE *，并且您正在取消指向da->data[0]中第一个元素的指针，因此它不再是TYPE *类型的指针，即不再是指针，因此您需要

da->data is of type TYPE * and you are dereferencing a pointer to it's first element in da->data[0], so it's no longer of type TYPE * i.e. not a pointer, so you need

if(da->data[0].key == 2)

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