source: downloads/tcl8.5.2/compat/opendir.c @ 35

/* 
 * opendir.c --
 *
 *      This file provides dirent-style directory-reading procedures for V7
 *      Unix systems that don't have such procedures. The origin of this code
 *      is unclear, but it seems to have come originally from Larry Wall.
 *
 * RCS: @(#) $Id: opendir.c,v 1.4 2007/04/16 13:36:34 dkf Exp $
 */

#include "tclInt.h"

#undef DIRSIZ
#define DIRSIZ(dp) \
    ((sizeof (struct dirent) - (MAXNAMLEN+1)) + (((dp)->d_namlen+1 + 3) &~ 3))

/*
 * open a directory.
 */

DIR *
opendir(
    char *name)
{
    register DIR *dirp;
    register int fd;
    char *myname;

    myname = ((*name == '\0') ? "." : name);
    if ((fd = open(myname, 0, 0)) == -1) {
        return NULL;
    }
    dirp = (DIR *) ckalloc(sizeof(DIR));
    if (dirp == NULL) {
        /* unreachable? */
        close(fd);
        return NULL;
    }
    dirp->dd_fd = fd;
    dirp->dd_loc = 0;
    return dirp;
}

/*
 * read an old style directory entry and present it as a new one
 */
#ifndef pyr
#define ODIRSIZ 14

struct  olddirect {
    ino_t od_ino;
    char od_name[ODIRSIZ];
};
#else   /* a Pyramid in the ATT universe */
#define ODIRSIZ 248

struct  olddirect {
    long od_ino;
    short od_fill1, od_fill2;
    char od_name[ODIRSIZ];
};
#endif

/*
 * get next entry in a directory.
 */

struct dirent *
readdir(
    register DIR *dirp)
{
    register struct olddirect *dp;
    static struct dirent dir;

    for (;;) {
        if (dirp->dd_loc == 0) {
            dirp->dd_size = read(dirp->dd_fd, dirp->dd_buf, DIRBLKSIZ);
            if (dirp->dd_size <= 0) {
                return NULL;
            }
        }
        if (dirp->dd_loc >= dirp->dd_size) {
            dirp->dd_loc = 0;
            continue;
        }
        dp = (struct olddirect *)(dirp->dd_buf + dirp->dd_loc);
        dirp->dd_loc += sizeof(struct olddirect);
        if (dp->od_ino == 0) {
            continue;
        }
        dir.d_ino = dp->od_ino;
        strncpy(dir.d_name, dp->od_name, ODIRSIZ);
        dir.d_name[ODIRSIZ] = '\0'; /* insure null termination */
        dir.d_namlen = strlen(dir.d_name);
        dir.d_reclen = DIRSIZ(&dir);
        return &dir;
    }
}

/*
 * close a directory.
 */

void
closedir(
    register DIR *dirp)
{
    close(dirp->dd_fd);
    dirp->dd_fd = -1;
    dirp->dd_loc = 0;
    ckfree((char *) dirp);
}