C 編程：從文件中讀取數字行並將其存儲在數組中

Question

我對編程有點陌生，很抱歉提出一個愚蠢的問題。 我的任務是讀取前兩行（數字）並將它們存儲為變量 n，另一行存儲在 m 中。 需要讀取這兩行下面的其他數字並將其存儲在動態數組中（確切地說是 malloc）。 每行只有一個數字。 我很難做到這一點。

到目前為止，這是我的代碼：

#include <stdio.h>
#define MAX_LINE 5

int main() {

    FILE* in;
    FILE* out;
    int n, m, list = (int*)malloc(9 * sizeof(int));

    in = fopen("ulazna.txt", "r");
    out = fopen("izlazna.txt","w");

    if ((in && out) == NULL)
    {
        printf("Error opening the file...");
        return -1;
    }

    while (fscanf(in, "%d\n", &m) != EOF)
    {
        fscanf(in, "%d\n", &n);
        fscanf(in, "%d\n", &m);
        printf("First two: %d %d", n, m);
    }

    //free(list);
    fclose(in);
    fclose(out);
    return 0;
}

文件 ulazna.txt 有：

3
3

這按預期工作，但是當我寫時：

3
3
1
2
3
4
5
6
7
8
9

我的程序從此文件中打印隨機數。

所以，我需要將 3 和 3 讀入 n 和 m。 然后，從 1 到 9 進入數組列表。

提前感謝您的幫助:)

Answer 1

動態數組大小

如果要為列表動態分配 memory，則必須先計算文件中的行數。

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

int main(void)
{
    int n, m;
    /* open the file for reading text using "r" */
    FILE *file_in = fopen("ulazna.txt", "r");

    if (!file_in) { /* same as `file_in == NULL` */
        printf("Failed to open file\n");
        return EXIT_FAILURE;
    }

    int lines = 0; /* number of lines */
    int c; /* return value of `fgetc` is of type `int` */

    /* go through each character in the file */
    while ((c = fgetc(file_in)) != EOF) {
       /* increment the number of lines after every line break */
       if(c == '\n')
           ++lines;
    }

    /* reset pointer to start of file */
    rewind(file_in);

    /* check the return value of `fscanf` */
    if (fscanf(file_in, "%d\n", &n) != 1 ||
            fscanf(file_in, "%d\n", &m) != 1) {
        printf("File contains invalid line\n");
        return EXIT_FAILURE;
    }
    printf("First two: %d %d\n", n, m);

    /* no need to cast `malloc`, because it returns `void *` */
    int *list = malloc(lines * sizeof(int));
    for (int i = 0; i < lines - 2; ++i) {
        /* check the return value of `fscanf` */
        if (fscanf(file_in, "%d\n", &list[i]) != 1) {
            printf("File contains invalid line\n");
            return EXIT_FAILURE;
        }
        printf("%d\n", list[i]);
    }

    free(list); /* always free memory allocated by malloc */
    fclose(file_in);
    return EXIT_SUCCESS;
}

固定數組大小

如果您已經知道文件中的行數將是 11，則數組的長度為 9，無需動態分配 memory。 但是因為你的任務需要它，我已經實現malloc 。

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

int main(void)
{
    int n, m;
    /* open the file for reading text using "r" */
    FILE *file_in = fopen("ulazna.txt", "r");

    if (!file_in) { /* same as `file_in == NULL` */
        printf("Failed to open file\n");
        return EXIT_FAILURE;
    }

    /* check the return value of `fscanf` */
    if (fscanf(file_in, "%d\n", &n) != 1 ||
            fscanf(file_in, "%d\n", &m) != 1) {
        printf("File contains invalid line\n");
        return EXIT_FAILURE;
    }
    printf("First two: %d %d\n", n, m);

    /* the array has a fixed size of 9 */
    const int size = 9;
    int *list = malloc(size * sizeof(int));
    /* 
     * If you do not have to use malloc, remove the
     * above line and uncomment the following line:
     *
     * int list[size];
     */
    for (int i = 0; i < size; ++i) {
        /* check the return value of `fscanf` */
        if (fscanf(file_in, "%d\n", &list[i]) != 1) {
            printf("File contains invalid line or has to few lines\n");
            return EXIT_FAILURE;
        }
        printf("%d\n", list[i]);
    }

    fclose(file_in);
    return EXIT_SUCCESS;
}