“구조 나 노조가 아닌 구성원 '*******'에 대한 요청”은 무엇을 의미합니까?

“구조 나 노조가 아닌 구성원 '*******'에 대한 요청”은 무엇을 의미합니까?

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이 오류가 의미하는 바에 대한 쉬운 설명이 있습니까?

request for member '*******' in something not a structure or union

나는 C를 배우면서 여러 번 만났지만 그것이 무엇을 의미하는지에 대한 단서가 없습니다.

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포인터가있을 때 인스턴스에 액세스하려는 경우에도 발생하며 그 반대의 경우도 마찬가지입니다.

struct foo
{
  int x, y, z;
};

struct foo a, *b = &a;

b.x = 12;  /* This will generate the error, should be b->x or (*b).x */

주석에서 지적했듯이 누군가가 typedef포인터를 sa 로 가면 , 즉 다음 *과 같이 typedef에를 포함하면 극심한 상황이 될 수 있습니다 .

typedef struct foo* Foo;

그러면 실제로 포인터를 처리 할 때 인스턴스를 처리 하는 것처럼 보이는 코드가 생성되기 때문입니다.

Foo a_foo = get_a_brand_new_foo();
a_foo->field = FANTASTIC_VALUE;

위의 내용이 작성되어야하는 것처럼 보이지만 struct에 대한 포인터 a_foo.field이므로 실패 Foo합니다. 나는 C의 : ed 포인터에 대해 강력히 추천합니다 typedef. 포인터는 중요합니다. 별표를 숨기지 마십시오. 빛나게하십시오.

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구조의 구성원에 액세스하려고하지만 구조가 아닌 것입니다. 예를 들면 :

struct {
    int a;
    int b;
} foo;
int fum;
fum.d = 5;

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다음과 같은 경우에도 발생할 수 있습니다.

예. 스택의 푸시 기능을 고려하면 :

typedef struct stack
{
    int a[20];
    int head;
}stack;

void push(stack **s)
{
    int data;
    printf("Enter data:");
    scanf("%d",&(*s->a[++*s->head])); /* this is where the error is*/
}

main()
{
    stack *s;
    s=(stack *)calloc(1,sizeof(stack));
    s->head=-1;
    push(&s);
    return 0;
}

오류는 푸시 기능과 주석 처리 된 줄에 있습니다. 포인터 s는 괄호 안에 포함되어야합니다. 올바른 코드 :

scanf("%d",&( (*s)->a[++(*s)->head]));

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이 오류가 코드 및 아래 주석에서 발생할 수있는 모든 경우를 열거했습니다. 더 많은 사례를 발견하면 추가하십시오.

#include<stdio.h>
#include<malloc.h>

typedef struct AStruct TypedefedStruct;

struct AStruct
{
    int member;
};

void main()
{
    /*  Case 1
        ============================================================================
        Use (->) operator to access structure member with structure pointer, instead
        of dot (.) operator. 
    */
    struct AStruct *aStructObjPtr = (struct AStruct *)malloc(sizeof(struct AStruct));
    //aStructObjPtr.member = 1;      //Error: request for member ‘member’ in something not 
                                      //a structure or union. 
                                      //It should be as below.
    aStructObjPtr->member = 1;
    printf("%d",aStructObjPtr->member); //1


    /*  Case 2
        ============================================================================
        We can use dot (.) operator with struct variable to access its members, but 
        not with with struct pointer. But we have to ensure we dont forget to wrap 
        pointer variable inside brackets.
    */
    //*aStructObjPtr.member = 2;     //Error, should be as below.
    (*aStructObjPtr).member = 2;
    printf("%d",(*aStructObjPtr).member); //2


    /* Case 3
       =============================================================================
       Use (->) operator to access structure member with typedefed structure pointer, 
       instead of dot (.) operator. 
    */
    TypedefedStruct *typedefStructObjPtr = (TypedefedStruct *)malloc(sizeof(TypedefedStruct));
    //typedefStructObjPtr.member=3;  //Error, should be as below.
    typedefStructObjPtr->member=3;
    printf("%d",typedefStructObjPtr->member);  //3


    /*  Case 4
        ============================================================================
        We can use dot (.) operator with struct variable to access its members, but 
        not with with struct pointer. But we have to ensure we dont forget to wrap 
        pointer variable inside brackets.
    */
    //*typedefStructObjPtr.member = 4;  //Error, should be as below.    
    (*typedefStructObjPtr).member=4;
    printf("%d",(*typedefStructObjPtr).member);  //4


    /* Case 5
       ============================================================================
       We have to be extra carefull when dealing with pointer to pointers to 
       ensure that we follow all above rules.
       We need to be double carefull while putting brackets around pointers.
    */

    //5.1. Access via struct_ptrptr and  ->
    struct AStruct **aStructObjPtrPtr = &aStructObjPtr;
    //*aStructObjPtrPtr->member = 5;  //Error, should be as below.
    (*aStructObjPtrPtr)->member = 5;
    printf("%d",(*aStructObjPtrPtr)->member); //5

    //5.2. Access via struct_ptrptr and .
    //**aStructObjPtrPtr.member = 6;  //Error, should be as below.
    (**aStructObjPtrPtr).member = 6;
    printf("%d",(**aStructObjPtrPtr).member); //6

    //5.3. Access via typedefed_strct_ptrptr and ->
    TypedefedStruct **typedefStructObjPtrPtr = &typedefStructObjPtr;
    //*typedefStructObjPtrPtr->member = 7;  //Error, should be as below.
    (*typedefStructObjPtrPtr)->member = 7;
    printf("%d",(*typedefStructObjPtrPtr)->member); //7

    //5.4. Access via typedefed_strct_ptrptr and .
    //**typedefStructObjPtrPtr->member = 8;  //Error, should be as below.
    (**typedefStructObjPtrPtr).member = 8;
    printf("%d",(**typedefStructObjPtrPtr).member); //8

    //5.5. All cases 5.1 to 5.4 will fail if you include incorrect number of *
    //     Below are examples of such usage of incorrect number *, correspnding
    //     to int values assigned to them

    //(aStructObjPtrPtr)->member = 5; //Error
    //(*aStructObjPtrPtr).member = 6; //Error 
    //(typedefStructObjPtrPtr)->member = 7; //Error 
    //(*typedefStructObjPtrPtr).member = 8; //Error
}

기본 아이디어는 다음과 같습니다.

• Use . with structure variable. (Cases 2 and 4)
• Use -> with pointer to structure. (Cases 1 and 3)
• If you reach structure variable or pointer to structure variable by following pointer, then wrap the pointer inside bracket: (*ptr). and (*ptr)-> vs *ptr. and *ptr-> (All cases except case 1)
• If you are reaching by following pointers, ensure you have correctly reached pointer to struct or struct whichever is desired. (Case 5, especially 5.5)

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It may means that you forgot include a header file that define this struct/union. For example:

foo.h file:

typedef union
{
    struct
    {
        uint8_t FIFO_BYTES_AVAILABLE    : 4;
        uint8_t STATE                   : 3;
        uint8_t CHIP_RDY                : 1;
    };
    uint8_t status;
} RF_CHIP_STATUS_t;

RF_CHIP_STATUS_t getStatus();

main.c file:

.
.
.
if (getStatus().CHIP_RDY) /* This will generate the error, you must add the  #include "foo.h" */
.
.
.

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can also appear if:

struct foo {   int x, int y, int z }foo; 

foo.x=12

instead of

struct foo {   int x; int y; int z; }foo; 

foo.x=12

참고URL : https://stackoverflow.com/questions/2184419/what-does-request-for-member-in-something-not-a-structure-or-union-m