#include <stdio.h>
int fseek(FILE  *stream, long  int  offset, int  origin);
返回：成功为0，出错为非0 

#include <stdio.h>
long int ftell(FILE *stream);

返回与流stream相关的文件的当前位置。出错时返回-1L。

头文件：#include <sys/types.h>    #include <unistd.h>定义函数：off_t lseek(int fildes, off_t offset, int whence);

 enum _flags{_READ     = 01,_WRITE     = 02,_UNBUF     = 04,_EOF    = 010,_ERR    = 020};

/* Gregory Pietsch -- My category 0 solution to 8-4 */int fseek(FILE *f, long offset, int whence)
{if ((f->flag & _UNBUF) == 0 && base != NULL)
{/* deal with buffering */if (f->flag & _WRITE)
{/* writing, so flush buffer */fflush(f);  /* from 8-3 */} 　　　　  else if (f->flag & _READ)
{/* reading, so trash buffer */f->cnt = 0;f->ptr = f->base;}}return (lseek(f->fd, offset, whence) < 0);
}

/*[The following solution is in the zip file as krx80401.c - RJH (ed.) ]EXERCISE 8-4I thought I'd improve 8-4 too.  I'm trying my best to get this as close
to ISO C as possible given the restrictions that I'm under.  (A real
implementation would have fsetpos() borrow some of the same code.)*//* Gregory Pietsch -- My category 0 solution to 8-4 */#define SEEK_SET 0
#define SEEK_CUR 1
#define SEEK_END 2int fseek(FILE *f, long offset, int whence)
{int result;if ((f->flag & _UNBUF) == 0 && base != NULL) {/* deal with buffering */if (f->flag & _WRITE) {/* writing, so flush buffer */if (fflush(f))return EOF;  /* from 8-3 */} else if (f->flag & _READ) {/* reading, so trash buffer --* but I have to do some housekeeping first*/if (whence == SEEK_CUR) {/* fix offset so that it's from the last * character the user read (not the last* character that was actually read)*/if (offset >= 0 && offset <= f->cnt) {/* easy shortcut */f->cnt -= offset;f->ptr += offset;f->flags &= ~_EOF; /* see below */return 0;} elseoffset -= f->cnt;}f->cnt = 0;f->ptr = f->base;}}result = (lseek(f->fd, offset, whence) < 0);if (result == 0)f->flags &= ~_EOF; /* if successful, clear EOF flag */return result;
}