So I have an assignment that I have been attempting for 2 weeks now and the class has been given extensions twice now. Everyone seems to be struggling with this part of the assignment. The assignment is to do K&R Exercise 5-13, unix tail command.
Instructions: "The program takes lines from standard input and keeps the last n of them in memory as it goes through standard input. When it gets to an EOF, it prints the last n lines out. You may assume n is less than 2000 and each individual line is not longer than 1000 including the newline and the null terminator.
Use two source files plus a header file for this, just to show you know how to make multiple source files work together.
tail.c:
interprets the command line argument.
Calls init_lineholder(int nlines) with the numebr from the command line.
Does a loop calling getline and insert_line(char *line)
when getline returns 0 (indicating EOF on stdin), it calls print_lines().
lineholder.c
contains a static array of pointers for lines.
Implements init_lineholder, insert_line, and print_lines.
Init_lineholder initializes the "first" slot and related variables.
Insert_line adds a line to the array.
It must allocate memory for the new line.
It must free the memory for a line no longer needed, if any.
Print_lines prints the lines in the array and frees the memory used for them.
lineholder.h: Just has prototypes for the three calls with appropriate comments explaining what they do for the caller.
Sources:
blade71(148)% cat lineholder.h
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
/* This header file contains the prototypes of the three functions
in lineholder.c */
int init_lineholder(int nlines);
int insert_line(char *line);
void print_lines();lineholder.c is correct, however I need to implement memory allocation.
blade71(160)% cat lineholder.c
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static char lines;
lines = *(*lines + MAXLEN) + MAXLINE);
static char (*first) [MAXLEN], (*last) [MAXLEN], (*end) [MAXLEN];
static int wrapped;
void init_lineholder(int lines)
{
if (nlines > MAXLINE)
nlines = MAXLINE;
first = last = lines;
end = lines + nlines;
wrapped = 0;
}
void insert_line(char *line)
{
strcpy(*last++, line);
if (wrapped)
first = (++first >= end) ?
lines : first;
if (last >= end)
{
last = lines;
wrapped = 1;
}
}
void print_lines(void)
{
do {
if (*first != NULL)
printf("%s", *first);
first = (++first >= end) ?
lines : first;
}
}Biggest mess of them all....:
blade71(188)% cat tail.c
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXLINE 2000
#define maxlen 1000
int getline(char *line, int max);
int main (int argc, char *argv[])
{
int nlines = 0;
char line[MAXLINE];
if (argc != 2)
printf("Too few of arguments");
else
{
while (getline(line, MAXLINE) > 0)
{
nlines++;
}
return nlines;
print_lines();
/* Calls init_lineholder(int nlines) with nlines */
/* Does loop callinggetline and insert_line(char*line) */
/* When getline returns 0, call print_lines() */
}
}
int getline(char *line, int max)
{
int nch = 0;
int c;
max = max - 1; /* leave room for '\0' */
#ifndef FGETLINE
while((c = getchar()) != EOF)
#else
while((c = getc(fp)) != EOF)
#endif
{
if(c == '\n')
break;
if(nch < max)
{
line[nch] = c;
nch = nch + 1;
}
}
if(c == EOF && nch == 0)
return EOF;
line[nch] = '\0';
return nch;
}