writeptr.c

APUE(第二版)的随书源代码,与第一版的代码相比增加了一些章节的代码(详见第二版的说明)

#include	"db.h"

/* Write a chain ptr field somewhere in the index file:
 * the free list, the hash table, or in an index record. */

void
_db_writeptr(DB *db, off_t offset, off_t ptrval)
{
	char	asciiptr[PTR_SZ + 1];

	if (ptrval < 0 || ptrval > PTR_MAX)
		err_quit("invalid ptr: %d", ptrval);
	sprintf(asciiptr, "%*d", PTR_SZ, ptrval);

	if (lseek(db->idxfd, offset, SEEK_SET) == -1)
		err_dump("lseek error to ptr field");
	if (write(db->idxfd, asciiptr, PTR_SZ) != PTR_SZ)
		err_dump("write error of ptr field");
}