nextrec.c

UNIX编程高级环境（第二版）的网络套接字部分的程序源码

#include    "db.h"

/* Return the next sequential record.
 * We just step our way through the index file, ignoring deleted
 * records.  db_rewind() must be called before this is function
 * is called the first time.
 */

char *
db_nextrec(DB *db, char *key)
{
    char    c, *ptr;

        /* We read lock the free list so that we don't read
           a record in the middle of its being deleted. */
    if (readw_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
        err_dump("readw_lock error");

    do {
            /* read next sequential index record */
        if (_db_readidx(db, 0) < 0) {
            ptr = NULL;        /* end of index file, EOF */
            goto doreturn;
        }
            /* check if key is all blank (empty record) */
        ptr = db->idxbuf;
        while ( (c = *ptr++) != 0  &&  c == ' ')
            ;    /* skip until null byte or nonblank */
    } while (c == 0);    /* loop until a nonblank key is found */

    if (key != NULL)
        strcpy(key, db->idxbuf);    /* return key */
    ptr = _db_readdat(db);    /* return pointer to data buffer */

    db->cnt_nextrec++;
doreturn:
    if (un_lock(db->idxfd, FREE_OFF, SEEK_SET, 1) < 0)
        err_dump("un_lock error");

    return(ptr);
}