循环条件问题 - 文件结束

Question

当前代码迭代：

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

#define MAX_LINE_SIZE 60
#define MAX_LIST_SIZE 15
#define MAX_QUIZ_SIZE 10

typedef struct question {
    char *question;
    char **choices;
    int n_choices;
    char *correct_answer;
} QUESTION;

char *dupString(const char *s) {
    // copies a string
    // CHECK TO SEE IF DUP WORKS

    char *dup = malloc(strlen(s) + 1);
    if (strcpy(dup, s)) {
        return dup;
    } else {
        printf("Error duplicating string");
        return 0;
    }
}

void free_question(QUESTION *q) {
    // free memory
    for(int i = 0; i < q->n_choices; i++) {
        free(q->choices[i]);
    }
    free(q->choices);
    free(q->question);
    free(q->correct_answer);

    // set pointers to null
    for(int i = 0; i < q->n_choices; i++) {
       q->choices[i] = NULL;
    }
    q->choices = NULL;
    q->question = NULL;
    q->correct_answer = NULL;
}

static int read_info(FILE *pData, char **ptr)
{
    char line[MAX_LINE_SIZE];
    if (fgets(line, sizeof(line), pData) == 0 ||
        (*ptr = dupString(line)) == 0)
        return EOF;
    return 0;
}

static int read_number(FILE *pData, int *num, QUESTION *q)
{
    char line[MAX_LINE_SIZE];
    if (fgets(line, sizeof(line), pData) == 0 ||
        (*num = atoi(line)) < 2 || q->n_choices > 9)
        return EOF;
    return 0;
}

static int read_choices(FILE *pData, QUESTION *q)
{
    char line[MAX_LINE_SIZE];
    for (int i = 0; i < q->n_choices; i++)
    {
        if (fgets(line, sizeof(line), pData) == 0 ||
            (q->choices[i] = dupString(line)) == 0)
            return EOF;
    }
    return 0;
}

int parseQuestion(FILE *pData, int qnum, QUESTION *q)
{
    *q = (QUESTION){ NULL, NULL, 0, NULL };

    if (read_info(pData, &q->question) == EOF ||
        read_number(pData, &q->n_choices, q) == EOF ||
        (q->choices = calloc(q->n_choices, sizeof(char *))) == 0 ||
        read_choices(pData, q) == EOF ||
        read_info(pData, &q->correct_answer) == EOF)
    {

        return EOF;
    }

    return 0;
}

struct question makeQuestion(FILE *pData, QUESTION *q) {

    int qIndex, numChoices; 
    char question[MAX_LINE_SIZE], temp[MAX_LINE_SIZE], choices[MAX_LINE_SIZE], correctAns[MAX_LINE_SIZE];

    // Eat first line = QUESTION
    fgets(question, MAX_LINE_SIZE, pData);
    q->question = dupString(question);


    // Eat second line = NUMBER OF CHOICES
    fgets(temp, MAX_LINE_SIZE, pData);
    numChoices = atoi(temp);
    q->n_choices = numChoices;

    // Allocate memory
    q->choices = calloc(q->n_choices, sizeof(char*));

    // Eat nth lines = CHOICES
    for (qIndex=0; qIndex<=numChoices-1; qIndex++) {
        fgets(choices, MAX_LINE_SIZE, pData);
        q->choices[qIndex] = dupString(choices);
    }

    // Eat nth + 1 line = CORRECT ANSWER
    fgets(correctAns, MAX_LINE_SIZE, pData);
    q->correct_answer = dupString(correctAns);

    return *q;  
}           

int ask(QUESTION *q) {
    // Return 1 for correct guess, 0 for incorrect guess.

    int choice;

    printf("\n%s\n", q->question);

    for (int i = 0; i <= q->n_choices-1; i++) {
        printf("%d : %s", i+1, q->choices[i]);
    }

    do {
        printf("Select an answer [1-%d]: ", q->n_choices);
        scanf("%d", &choice);

        if (choice == 0) {
            return 2;
        }

        /* Check guess */
        int ret;
        size_t size = sizeof(q->correct_answer);
        ret = memcmp(q->choices[choice-1], q->correct_answer, size);

        if (ret == 0) {
            return 1;
        }
    } while (choice < 1 || choice > q->n_choices);

    return 0;
}


int main() {

    int num = 0;        // question being asked
    int score = 0;  // incorrect guesses
    char temp[MAX_LINE_SIZE]; // temp for loop condition

    FILE* pData;

    char *filename = "tickle.txt";
    char c;

    if ((pData = fopen(filename, "r"))) {

        printf("Welcome to the 2014 Quiz-festival!\n\n");
        printf("Are you ready to begin? [Y/y]:  ");
        c = getchar();

        if (c == 'Y' || c == 'y') {

            QUESTION q;
            while (parseQuestion(pData, ++num, &q) == 0) {
                makeQuestion(pData, &q);

                if (ask(&q) == 1) {
                    ++score;
                    printf("Correct!\n");
                } else {
                    printf("Oops, bad luck!\n");
                }
                free_choices(&q);
            }       

        } else {
            printf("Come back again.\n");
            return 0;
        }

    } else {
        printf("File failed to open.");
        return 0;
    }

    fclose(pData);
    return 0;
}

它似乎正在起作用，但它从第二次测验开始。现在我完全糊涂了。

示例数据文件：

  

问题1

     

3（答案数量）

     

答案1a

     

回答1b

     

回答1c

     

答案1a（这是正确答案）

     

问题2

     

2

     

答案2a

     

回答2b

     

答案2b（这是正确答案）

程序从问题2开始。内存是否有问题？我似乎无法绕过它。

Answer 1

由于parseQuestion()函数是检测EOF的函数，因此它应返回一个值，指示是否存在要处理的问题（如果没有，则假设为EOF）。

考虑到这种情况，我可能会重写其界面：

QUESTION question;
while (parseQuestion(pData, ++num, &question) == 0)
{
    …process a known-to-be-valid question…
}

我让它做提示，传递文件指针，问题编号和指向它将填写的问题结构的指针。成功时会返回0和其他一些值（也许是EOF）失败。

这或多或少是在C中处理此类问题的标准方法。退后一步，检查fgets()是如何工作的：

char line[4096];
while (fgets(line, sizeof(line), fp) != 0)
{
    …process line…
}

---

您可以像这样重写parseQuestion()：

int parseQuestion(FILE *pData, int qnum, QUESTION *q)
{
    char line[MAX_LINE_SIZE];

    *q = (QUESTION){ NULL, NULL, 0, NULL };

    printf("******** Question: %d ********\n", num);

    if (fgets(line, sizeof(line), pData) == 0 ||
        (q->question = dupString(line)) == 0)
        return EOF;

    if (fgets(line, sizeof(line), pData) == 0)
    {
        free_choices(q);
        return EOF;
    }
    q->n_choices = atoi(line);
    if (q->n_choices < 2 || q->n_choices > 9)
    {
        fprintf(stderr, "Invalid number of choices %d (should be 2..9)\n",
                q->n_choices);
        free_choices(q);
        return EOF;
    }

    q->choices = calloc(q->n_choices, sizeof(char *));
    if (q->choices == 0)
    {
        fprintf(stderr, "Memory allocation failed)\n");
        free_choices(q);
        return EOF;
    }

    for (int i = 0; i < q->n_choices; i++)
    {
        if (fgets(line, sizeof(line), pData) == 0 ||
            (q->choices[i] = dupString(line)) == 0)
        {
            free_choices(q);
            return EOF;
        }
    }

    if (fgets(line, sizeof(line), pData) == 0 ||
        (q->correct_answer = dupString(line)) == 0)
    {
        free_choices(q);
        return EOF;
    }

    return 0;
}

然而，错误处理中的代码中有很多重复;你可能更愿意尝试摆脱它的一些。你可以在第一个free_choices()之前调用return EOF;，但它没有任何关系（但是当你处理错误时，边际性能开销并不重要）。使用calloc()分配指针数组很重要;这意味着当数组部分填充时，您可以安全地调用free_choices()。这样的观察导致：

static int read_info(FILE *pData, char **ptr)
{
    char line[MAX_LINE_SIZE];
    if (fgets(line, sizeof(line), pData) == 0 ||
        (*ptr = dupString(line)) == 0)
        return EOF;
    return 0;
}

static int read_number(FILE *pData, int *num)
{
    char line[MAX_LINE_SIZE];
    if (fgets(line, sizeof(line), pData) == 0 ||
        (*num = atoi(line)) < 2 || q->n_choices > 9)
        return EOF;
    return 0;
}

static int read_choices(FILE *pdata, QUESTION *q)
{
    for (int i = 0; i < q->n_choices; i++)
    {
        if (fgets(line, sizeof(line), pData) == 0 ||
            (q->choices[i] = dupString(choices)) == 0)
            return EOF;
    }
    return 0;
}

int parseQuestion(FILE *pData, int qnum, QUESTION *q)
{
    printf("******** Question: %d ********\n", num);
    *q = (QUESTION){ NULL, NULL, 0, NULL };

    if (read_info(pData, &q->question) == EOF ||
        read_number(pData, &q->n_choices) == EOF ||
        (q->choices = calloc(q->n_choices, sizeof(char *))) == 0 ||
        read_choices(pData, q) == EOF ||
        read_info(pData, &q->correct_answer) == EOF)
    {
        free_choices(q);
        return EOF;
    }

    return 0;
}

您可以read_choices()反复调用read_info()，而不是在read_info()内实施read_choices()。任何代码通常都有改进的余地。