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/*****************************************************************************
tail
DESCRIPTION: tail prints the last -n lines of a input, if n is not give it
prints 10 lines by default, no malloc or stcpy is used in this version and
stack storage is allocated in the most efficent way for each line
*****************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define DEFAULT_N 10
#define MAXLEN 1000
#define MAXLINE 5000
#define BUFFSIZE MAXLEN * MAXLINE
char buff[BUFFSIZE];
char *lineptr[MAXLINE];
int buff_now;
int lineptr_now;
int line_no;
void get_tail(void);
int sneed_getline(char str[], int max);
void pr_tail(int nlines);
int
main(int argc, char **argv)
{
int nlines = 0;
if (--argc == 1 && **(++argv) == '-' && isdigit(*++*argv)) {
for (; isdigit(**argv) ; ++*argv)
nlines = nlines * 10 + **argv - '0';
}
else if (argc != 0)
argc = -1;
if (!nlines)
nlines = DEFAULT_N;
if ( argc >= 0 && nlines > 0 && nlines < MAXLINE) {
get_tail();
pr_tail(nlines);
}
else
printf("Usage: tail -n\n");
}
void
get_tail(void) {
int len;
while ((len = sneed_getline(buff + buff_now, MAXLEN)) > 0) {
lineptr[lineptr_now] = buff + buff_now ;
line_no++;
buff_now = (buff_now + MAXLEN >= BUFFSIZE -1) ? 0 : buff_now + len + 1;
lineptr_now = (lineptr_now >= MAXLINE - 1) ? 0 : lineptr_now + 1;
}
}
void
pr_tail(int nlines)
{
if (line_no < nlines)
nlines = line_no;
lineptr_now = (lineptr_now - nlines < 0) ? MAXLINE - 1 + lineptr_now - nlines : lineptr_now - nlines;
while(nlines--) {
printf("%s", lineptr[lineptr_now]);
lineptr_now = (lineptr_now >= MAXLINE - 1) ? 0 : lineptr_now + 1;
}
}
int
sneed_getline(char str[], int max)
{
char input;
char *str_og;
str_og = str;
--max;
while (--max && (input = getchar()) != EOF && input != '\n')
*str++ = input;
if (input == '\n' && max)
*str++ = input;
*str = '\0';
return str - str_og;
}
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