head/tail实现，headtail实现
只实现了head/tail的基本功能，默认显示十行及-n参数。
一、使用带缓冲的系统调用。
write/read等系统调用是不带缓冲的，可以包装一层，使其带缓冲。
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typedef
struct
{
int rio_fd;
int rio_cnt;
char *
rio_bufptr;
char rio_buf[RIO_BUFFSIZE];
}rio_t;
void rio_readinitb(rio_t *rp,
int fd)
{
rp->rio_fd =
fd;
rp->rio_cnt =
0;
rp->rio_bufptr = rp->
rio_buf;
}
ssize_t rio_read(rio_t *rp,
void *
usrbuf, size_t n)
{
int cnt =
0;
while (rp->rio_cnt <=
0)
{
if ((rp->rio_cnt = read(rp->rio_fd, rp->rio_buf,
sizeof(rp->rio_buf))) <
0)
{
if (errno !=
EINTR)
{
return -
1;
}
}
else if (rp->rio_cnt ==
0)
{
return 0;
}
else
{
rp->rio_bufptr = rp->
rio_buf;
}
}
//cnt = n > rp->rio_cnt?rp->rio_cnt:n;
cnt =
n;
if (n > rp->
rio_cnt)
{
cnt = rp->
rio_cnt;
}
memcpy(usrbuf, rp->
rio_bufptr, cnt);
rp->rio_cnt -=
cnt;
rp->rio_bufptr +=
cnt;
return cnt;
}
ssize_t rio_readlineb(rio_t *rp,
void *usrbuf, size_t maxlen,
int count)
{
int i =
0, rc =
0, num =
0;
char c =
0, *buf =
usrbuf;
lseek(rp->
rio_fd, maxlen, SEEK_END);
for (i =
1; i < maxlen; i++
)
{
if ((rc = rio_read(rp, &c,
1)) ==
1)
{
*buf++ =
c;
if (c ==
'\n')
{
if (++num ==
count)
{
break;
}
}
}
else if (rc ==
0)
{
if (i ==
1)
{
return 0;
}
else
{
break;
}
}
else
{
return -
1;
}
}
*buf =
'\0';
return i;
}
View Code
二、head命令实现
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#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <
string.h>
#include "rio.h"
#define MAXSIZE 4096
int main(
int argc,
char **
argv)
{
if (argc <
2)
{
fprintf(stderr, "usage %s [-n n] filename\n", argv[
0]);
return -
1;
}
int times =
10, i =
0, in_fd = -
1, n_char =
0;
char filename[
16] = {
0};
char buf[MAXSIZE] = {
0};
rio_t rio_buf = {
0};
for (i =
1; i < argc; i++
)
{
if (!strcmp(argv[i],
"-n"))
{
times = atoi(argv[++
i]);
}
else
{
snprintf(filename, sizeof(filename),
"%s", argv[i]);
}
}
if ((in_fd = open(filename, O_RDONLY)) == -
1)
{
fprintf(stderr, "open %s failed\n", filename);
return -
1;
}
rio_readinitb(&
rio_buf, in_fd);
if ((n_char = rio_readlineb(&rio_buf, buf, MAXSIZE, times)) >
0)
{
write(STDOUT_FILENO, buf, n_char);
}
close(in_fd);
return 0;
}
View Code
三、tail命令实现
![]()
#include
"rio.h"
#define MAXSIZE 4096
void show_info(
char *buf,
char **ptr,
int count);
int main(
int argc,
char **
argv)
{
if (argc <
2)
{
fprintf(stderr, "usage %s [-n n] filename\n", argv[
0]);
return -
1;
}
int times =
10, i =
0, in_fd = -
1;
char filename[
16] = {
0};
char buf[MAXSIZE] = {
0};
rio_t rio_buf = {
0};
char *
ptr[MAXSIZE];
for (i =
1; i < argc; i++
)
{
if (!strcmp(argv[i],
"-n"))
{
times = atoi(argv[++
i]);
}
else
{
snprintf(filename, sizeof(filename),
"%s", argv[i]);
}
}
if ((in_fd = open(filename, O_RDONLY)) == -
1)
{
fprintf(stderr, "open %s failed\n", filename);
return -
1;
}
rio_readinitb(&
rio_buf, in_fd);
rio_read(&
rio_buf, buf, MAXSIZE);
show_info(buf, ptr, times);
return 0;
}
void show_info(
char *buf,
char **ptr,
int times)
{
int num =
0;
int flag =
0;
if (num <
times)
{
*ptr = strrchr(buf,
'\n');
flag =
1;
**ptr =
'\0';
show_info(buf, ptr +
1, --
times);
}
if (flag)
{
printf("%s\n", *ptr +
1);
}
}
View Code
通过递归show_info来实现按顺序打印，其实也可以用链表来实现，不过递归写起来简单。
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