dirs_links/list_files_readdir_r.c

This is dirs_links/list_files_readdir_r.c, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is the solution to Exercise 18-4 (page 373).

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

 

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  Cover of The Linux Programming Interface

Function list (Bold in this list means a function is not static)

/* list_files_readdir_r.c

   Demonstrate the use of opendir() and readdir_r() to list files
   in a directory.

   Usage: list_files_readdir_r [dir...]

   Walks through each directory named on the command line (current directory
   if none are specified) to display a list of the files it contains.

   See also list_files_readdir.c.
*/
#if defined(__APPLE__)
        /* Darwin requires this header before including <dirent.h> */
#include <sys/types.h>
#endif
#include <limits.h>
#include <dirent.h>
#include <stddef.h>
#include "tlpi_hdr.h"
static void             /* List all files in directory 'dirpath' */
listFiles(const char *dirpath)
{
    DIR *dirp;
    Boolean isCurrent;          /* True if 'dirpath' is "." */
    struct dirent *result, *entryp;
    int nameMax;

    isCurrent = strcmp(dirpath, ".") == 0;

    /* On Linux, NAME_MAX is defined in <limits.h>. However, this limit
       may vary across file systems, so we really should use pathconf()
       to find the true limit for this file system. */

    nameMax = pathconf(dirpath, _PC_NAME_MAX);
    if (nameMax == -1)          /* Indeterminate or error */
        nameMax = 255;          /* So take a guess */

    entryp = malloc(offsetof(struct dirent, d_name) + nameMax + 1);
    if (entryp == NULL)
        errExit("malloc");

    /* Open the directory - on failure print an error and return */

    dirp = opendir(dirpath);
    if (dirp == NULL) {
        errMsg("opendir failed on '%s'", dirpath);
        free(entryp);
        return;
    }

    /* Look at each of the entries in this directory */

    for (;;) {
        errno = readdir_r(dirp, entryp, &result);
        if (errno != 0)
            errExit("readdir_r");

        if (result == NULL)     /* End of stream */
            break;

        /* Skip . and .. */

        if (strcmp(entryp->d_name, ".") == 0 ||
                strcmp(entryp->d_name, "..") == 0)
            continue;

        /* Print directory + filename */

        if (!isCurrent) printf("%s/", dirpath);
        printf("%s\n", entryp->d_name);
    }

    if (closedir(dirp) == -1)
        errMsg("closedir");
}
int
main(int argc, char *argv[])
{
    if (argc == 1)              /* No arguments - use current directory */
        listFiles(".");
    else
        for (argv++; *argv; argv++)
            listFiles(*argv);
    exit(EXIT_SUCCESS);
}

 

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Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

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