大链表查找，求解决方法 - Chinaunix

/*
* scandir, alphasort - scan a directory
*
* implementation for systems that do not have it in libc
*/
#include "../config.h"
#ifndef HAVE_SCANDIR
#include <sys/types.h>
#include <dirent.h>
#include <stdlib.h>
#include <stddef.h>
#include <string.h>
/*
* convenience helper function for scandir's |compar()| function:
* sort directory entries using strcoll(3)
*/
int
alphasort(const void *_a, const void *_b)
{
struct dirent **a = (struct dirent **)_a;
struct dirent **b = (struct dirent **)_b;
return strcoll((*a)->d_name, (*b)->d_name);
}
#define strverscmp(a,b) strcoll(a,b) /* for now */
/*
* convenience helper function for scandir's |compar()| function:
* sort directory entries using GNU |strverscmp()|
*/
int
versionsort(const void *_a, const void *_b)
{
struct dirent **a = (struct dirent **)_a;
struct dirent **b = (struct dirent **)_b;
return strverscmp((*a)->d_name, (*b)->d_name);
}
/*
* The scandir() function reads the directory dirname and builds an
* array of pointers to directory entries using malloc(3). It returns
* the number of entries in the array. A pointer to the array of
* directory entries is stored in the location referenced by namelist.
*
* The select parameter is a pointer to a user supplied subroutine
* which is called by scandir() to select which entries are to be
* included in the array. The select routine is passed a pointer to
* a directory entry and should return a non-zero value if the
* directory entry is to be included in the array. If select is null,
* then all the directory entries will be included.
*
* The compar parameter is a pointer to a user supplied subroutine
* which is passed to qsort(3) to sort the completed array. If this
* pointer is null, the array is not sorted.
*/
int
scandir(const char *dirname,
struct dirent ***ret_namelist,
int (*select)(const struct dirent *),
int (*compar)(const struct dirent **, const struct dirent **))
{
int i, len;
int used, allocated;
DIR *dir;
struct dirent *ent, *ent2;
struct dirent **namelist = NULL;
if ((dir = opendir(dirname)) == NULL)
return -1;
used = 0;
allocated = 2;
namelist = malloc(allocated * sizeof(struct dirent *));
if (!namelist)
goto error;
while ((ent = readdir(dir)) != NULL) {
if (select != NULL && !select(ent))
continue;
/* duplicate struct direct for this entry */
len = offsetof(struct dirent, d_name) + strlen(ent->d_name) + 1;
if ((ent2 = malloc(len)) == NULL)
return -1;
if (used >= allocated) {
allocated *= 2;
namelist = realloc(namelist, allocated * sizeof(struct dirent *));
if (!namelist)
goto error;
}
memcpy(ent2, ent, len);
namelist[used++] = ent2;
}
closedir(dir);
if (compar)
qsort(namelist, used, sizeof(struct dirent *),
(int (*)(const void *, const void *)) compar);
*ret_namelist = namelist;
return used;
error:
if (namelist) {
for (i = 0; i < used; i++)
free(namelist[i]);
free(namelist);
}
return -1;
}
#endif
#if STANDALONE_MAIN
int
main(int argc, char **argv)
{
struct dirent **namelist;
int i, n;
n = scandir("/etc", &namelist, NULL, alphasort);
for (i = 0; i < n; i++)
printf("%s\n", namelist[i]->d_name);
}
#endif

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