Date: Thu, 28 Jun 2001 14:20:17 +0800 (CST) From: Tai-hwa Liang <avatar@mmlab.cse.yzu.edu.tw> To: <freebsd-stable@FreeBSD.org> Subject: lseek(SEEK_END) then read()... bug of feature? Message-ID: <Pine.BSF.4.33.0106281339090.72014-100000@www.mmlab.cse.yzu.edu.tw>
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Hi,
Anyone tried lseek() from the end of file then read something
out? I've tested the attached code on FreeBSD 4-stable. Both of the two
-stable box(cvsupped on May-02-2001 and Jun-19-2001) prints error
message(Undefined error: 0) on the first read(); however, the second
read() worked without any problem....
I've also tested this code on Linux(2.4.x) and Windoze 98. It
seemed that all read() returned correct result. Did I misunderstand
the meaning of lseek(2)?
------------------------------------------------------------------------
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
int
main()
{
unsigned int l = 0;
off_t offset;
int ret, fd = open("/kernel", O_RDONLY);
offset = 0 - sizeof(int);
lseek(fd, offset, SEEK_END);
if ((ret = read(fd, &l, sizeof(int))) != sizeof(int))
perror("read error in phase 1");
else
printf("read %d bytes in phase 1\n", ret);
offset = -4;
lseek(fd, offset, SEEK_END);
if ((ret = read(fd, &l, sizeof(int))) != sizeof(int))
perror("read error in phase 2");
else
printf("read %d bytes in phase 2\n", ret);
printf("result = 0x%x\n", l);
close(fd);
return (0);
}
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