c - 提供特定值但返回错误指针

Question

我有一个包含不同等级单词的结构。例如，如果你得到了 A 级，那么描述你的词就是“Brilliant”、“Fantastic”。如果你得到了 B 级，那么形容你的词就是“好”、“不错”。这些词存储为结构。

但是，我需要创建一个函数 (grade_pnter_finder)，我在其中解析成绩，如果是该成绩的头或尾，它会返回该成绩单词的结构。但是，无论成绩如何，它都会不断向我返回相同的指针。如果我给它尾部 A 级，它会返回指针 100。如果我给它尾部 B 级，它会返回指针 100。

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

struct grade {
    struct grade_word *A_head;
    struct grade_word *A_tail;

    struct grade_word *B_head;
    struct grade_word *B_tail;

    struct grade_word *C_head;
    struct grade_word *C_tail;

    struct grade_word *D_head;
    struct grade_word *D_tail;

    struct grade_word *E_head;
    struct grade_word *E_tail;

};

struct grade_word {
    char *word;
    int word_len;
    struct grade_word *next;
    struct grade_word *prev;
};

struct grade *create_grade() {

    struct grade *new_grade = malloc(sizeof(struct grade));

    // Check grade was allocated correctly
    if (new_grade == NULL) {
        fprintf(stderr, "ERROR: Could not allocate memory for grade\n");
        exit(1);
    }

    // Initialise all variables
    new_grade->A_head = NULL;
    new_grade->A_tail = NULL;
    new_grade->B_head = NULL;
    new_grade->B_tail = NULL;
    new_grade->B_head = NULL;
    new_grade->C_tail = NULL;
    new_grade->C_head = NULL;
    new_grade->C_tail = NULL;
    new_grade->D_head = NULL;
    new_grade->D_tail = NULL;
    new_grade->E_head = NULL;
    new_grade->E_tail = NULL;

    return new_grade;
}

struct grade_word *grade_pnter_finder(struct grade *grade_data, char grade,
                                      char h_or_t) {

    struct grade_word *target = NULL;
    if (grade == 'A') {
        if (h_or_t == 'H') {
            target = grade_data->A_head;
        } else {
            target = grade_data->A_tail;
        }
    } else if (grade == 'B') {
        if (h_or_t == 'H') {
            target = grade_data->B_head;
        } else {
            target = grade_data->B_tail;
        }
    } else if (grade == 'C') {
        if (h_or_t == 'H') {
            target = grade_data->C_head;
        } else {
            target = grade_data->C_tail;
        }
    } else if (grade == 'D') {
        if (h_or_t == 'H') {
            target = grade_data->D_head;
        } else {
            target = grade_data->D_tail;
        }
    } else {
        if (h_or_t == 'H') {
            target = grade_data->E_head;
        } else {
            target = grade_data->E_tail;
        }
    }

    if (h_or_t == 'H') printf("Grade %c's Head pointer is at: %p\n", grade, &target);
    else printf("Grade %c's Tail pointer is at: %p\n", grade, &target);
    return target;
}

int main(void) {

    struct grade *new_grade = create_grade();
    struct grade_word *pnter;
    pnter = grade_pnter_finder(new_grade, 'A', 'H');
    pnter = grade_pnter_finder(new_grade, 'A', 'T');
    pnter = grade_pnter_finder(new_grade, 'B', 'H');
    pnter = grade_pnter_finder(new_grade, 'B', 'T');
    pnter = grade_pnter_finder(new_grade, 'C', 'H');
    pnter = grade_pnter_finder(new_grade, 'C', 'T');
    pnter = grade_pnter_finder(new_grade, 'D', 'H');
    pnter = grade_pnter_finder(new_grade, 'D', 'T');
    pnter = grade_pnter_finder(new_grade, 'E', 'H');
    pnter = grade_pnter_finder(new_grade, 'E', 'T');

    printf("Stop compiler complaining for unused variable = %p\n", &pnter);


}

---

输出:

Grade A's Head pointer is at: 0028FEFC
Grade A's Tail pointer is at: 0028FEFC

Grade B's Head pointer is at: 0028FEFC
Grade B's Tail pointer is at: 0028FEFC

Grade C's Head pointer is at: 0028FEFC
Grade C's Tail pointer is at: 0028FEFC

Grade D's Head pointer is at: 0028FEFC
Grade D's Tail pointer is at: 0028FEFC

Grade E's Head pointer is at: 0028FEFC
Grade E's Tail pointer is at: 0028FEFC

Stop compiler complaining for unused variable = 0028FF28

如您所见，它们都指向同一个地方。不应该指向不同的地方吗？

Answer 1

如果您指的是打印的值:

if (h_or_t == 'H') printf("Grade %c's Head pointer is at: %p\n", grade, &target);
else printf("Grade %c's Tail pointer is at: %p\n", grade, &target);

您应该将&target 更改为target。你想打印局部变量的值，而不是它在内存中的存储位置。