head/tail實現，headtail實現
head/tail實現，headtail實現
只實現了head/tail的基本功能，默認顯示十行及-n參數。
一、使用帶緩沖的系統調用。
write/read等系統調用是不帶緩沖的，可以包裝一層，使其帶緩沖。
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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命令實現
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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命令實現
![]()
#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
通過遞歸show_info來實現按順序打印，其實也可以用鏈表來實現，不過遞歸寫起來簡單。
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