C编程: writing directory file names into an array,出现奇怪符号

Question

我试图将目录中每个文件的名称放入一个数组中。在我打印数组本身之前，代码似乎运行良好。

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

int main ()
{
    char directory_name[10];
    DIR *ptr;
    int n, i;

    n = 0;
    i = 0;

    //Ask user for directory name
    struct dirent *directory;
    printf ("Enter Directory Name:\t");
    scanf ("%s", directory_name);
    ptr = opendir (directory_name);
    printf ("\nDirectory %s\n", directory_name);

    while ((directory = readdir (ptr)) != NULL) {
        if (!strcmp (directory->d_name, ".")
            || !strcmp (directory->d_name, "..")) {

        } else {
            n++;
        }
    }

    rewinddir (ptr);

    char *filesList[n];

    //Put file names into the array
    while ((directory = readdir (ptr)) != NULL) {
        if (!strcmp (directory->d_name, ".")
            || !strcmp (directory->d_name, "..")) {
        } else {
            filesList[i] = (char *) malloc (strlen (directory->d_name) + 1);
            strncpy (filesList[i], directory->d_name,
                    strlen (directory->d_name));
            i++;
        }
    }
    rewinddir (ptr);

    for (i = 0; i <= n; i++) {
        printf ("%s\n", filesList[i]);
    }

    closedir (ptr);
    return 0;
}

filesList 会打印，但在打印输出的末尾，它会添加另一行带有这些符号:

)─ìD$â└┴Φ┴αëE╨θï

我想从数组中删除这些符号。然而，由于我不知道它们是什么或它们来自哪里，所以我什至不知道从哪里开始。我对 C 很陌生，所以如果这是一个初学者问题，我深表歉意。

我想澄清一下，程序将这些符号识别为文件名，即使目录中没有该名称的文件。索引会像文件一样增加。

Answer 1

不要在代码中使用魔数(Magic Number):

char directory_name[10];

如果您需要一个常量，请定义一个常量，或者如果已经为特定应用程序提供了适当的常量，请使用该常量，例如

#ifndef PATH_MAX        /* declare constants as required */
#define PATH_MAX 4096
#endif

#define NFILE 128
...
char directory_name[PATH_MAX] = "",
    ...

您无法绝对确定任何问题的根源在哪里，因为您未能验证任何所需的返回。除 void 之外的所有功能提供可用于指示成功或失败的返回值 - 使用它们，例如

    /* open and VALIDATE directory with opendir */
    ptr = opendir (directory_name);
    if (!ptr) {
        fprintf (stderr, "error: directory open failed '%s'.\n", 
                directory_name);
        return 1;
    }
    printf ("\nDirectory open '%s'\n", directory_name);

这是用户输入的绝对必须。

您填充的数组索引在 0 之间和n-1 ，所以你的索引 for (i = 0; i <= n; i++)通过读取超出 VLA 范围的内容来调用未定义行为。使用for (i = 0; i < n; i++)

不要对目录进行两次遍历(第一次计算文件数量，倒回，第二次读取文件名)，只需最初分配一些合理数量的 char 指针，跟踪您的数量填写，并且realloc当您达到当前限制时。下面的代码就是这样做的(以及清理用户输入——应该通过使用 fgets 而不是 scanf 来简化并变得更加健壮)，例如

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>
#include <limits.h>

#ifndef PATH_MAX        /* declare constants as required */
#define PATH_MAX 4096
#endif

#define NFILE 128

/* simple function to empty stdin.
 * mandatory when taking user input with scanf
 */
void empty_stdin()
{
    int c = getchar();

    while (c != '\n' && c != EOF)
        c = getchar();
}

int main (void) {

    DIR *ptr = NULL;
    struct dirent *directory = NULL;
    char directory_name[PATH_MAX] = "",
        **files = NULL;     /* using pointer to pointer to char */
    size_t i, n = 0, nptr = NFILE;

    /* prompt for and VALIDATE input of directory_name */
    for (;;) {     /* loop until valid input received or user cancels */
        int rtn;
        printf ("Enter Directory Name: ");
        rtn = scanf ("%s", directory_name);
        if (rtn == 1) {     /* good input, proceed */
            empty_stdin();
            break;
        }
        else if (rtn == EOF) {  /* user canceled input */
            fprintf (stderr, "user canceled input.\n");
            return 1;
        }   /* handle other error */
        fprintf (stderr, "error: invalid input.\n");
        empty_stdin();
    }

    /* open and VALIDATE directory with opendir */
    ptr = opendir (directory_name);
    if (!ptr) {
        fprintf (stderr, "error: directory open failed '%s'.\n", 
                directory_name);
        return 1;
    }
    printf ("\nDirectory open '%s'\n", directory_name);

    /* allocate and VALIDATE nptr pointer for filenames */
    files = calloc (nptr, sizeof *files);
    if (!files) {
        perror ("pointer allocation failed");
        return 1;
    }

    /* read each filename, allocate/VALIDATE storage, copy to files[n],
     * check total pointer allocation, realloc as required.
     */
    while ((directory = readdir (ptr)) != NULL) {
        if (!strcmp (directory->d_name, ".")    /* skip dot files */
            || !strcmp (directory->d_name, ".."))
            continue;
        /* allocate VALIDATE storage for filename */
        files[n] = malloc (strlen (directory->d_name) + 1);
        if (!files[n]) {
            perror ("memory exhausted - filesList");
            return 1;
        }
        strcpy (files[n++], directory->d_name); /* copy filename */
        /* check if ptr limit reached, if so realloc 2x pointers */
        if (n == nptr) {
            void *tmp = realloc (files, nptr * 2 * sizeof *files);
            if (!tmp) {
                perror ("realloc failed - files");
                break;  /* files still points to original block */
            }
            files = tmp;
            /* optional - zero all newly added memory */
            memset (files + nptr, 0, nptr * sizeof *files);
            nptr *= 2;  /* increment number currently allocated */
        }
    }

    for (i = 0; i < n; i++) {   /* indexes are 0 -> n-1 */
        printf ("%s\n", files[i]);
        free (files[i]);        /* don't forget to free memory */
    }
    free (files);   /* free pointers */

    closedir (ptr);

    return 0;
}

示例使用/输出

$ ./bin/readdir_alloc
Enter Directory Name: dat
Directory open 'dat'
lastchgcol.txt
arrinpt.txt
...

内存使用/错误检查

在您编写的动态分配内存的任何代码中，对于分配的任何内存块，您都有两个责任:(1) 始终保留指向起始地址的指针内存块，因此，(2) 当不再需要它时可以释放。

对于 Linux valgrind是正常的选择。每个平台都有类似的内存检查器。它们使用起来都很简单，只需通过它运行您的程序即可。

$ valgrind ./bin/readdir_alloc
==10547== Memcheck, a memory error detector
==10547== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==10547== Using Valgrind-3.11.0 and LibVEX; rerun with -h for copyright info
==10547== Command: ./bin/readdir_alloc
==10547==
Enter Directory Name: dat
Directory open 'dat'
lastchgcol.txt
arrinpt.txt
...
==10547==
==10547== HEAP SUMMARY:
==10547==     in use at exit: 0 bytes in 0 blocks
==10547==   total heap usage: 248 allocs, 248 frees, 38,729 bytes allocated
==10547==
==10547== All heap blocks were freed -- no leaks are possible
==10547==
==10547== For counts of detected and suppressed errors, rerun with: -v
==10547== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

始终确认您已释放分配的所有内存并且不存在内存错误。

使用fgets是接受用户输入的推荐方法。 scanf如果充满陷阱，会困住新的 C 程序员。 fgets只需检查返回结果，然后覆盖尾随 '\n' 即可。包含在带有 nul-termination 字符的缓冲区中。您可以删除整个 for循环，直到使用scanf接收到有效输入为止使用 fgets 使用以下简化代码:

    size_t len;
    printf ("Enter Directory Name: ");
    if (!fgets (directory_name, PATH_MAX, stdin)) {
        fprintf (stderr, "error: failed to read directory_name.\n");
        return 1;
    }
    len = strlen (directory_name);
    if (len && directory_name[len - 1] == '\n')
        directory_name[--len] = 0;
    else if (len + 1 == PATH_MAX) {
        fprintf (stderr, "error: directory_name too long.\n");
        return 1;
    }

仔细检查一下，如果您还有其他问题，请告诉我。