5.7.c

#include <stdio.h>
#include <string.h>
#include "lib/libkr.h"

#define MAXLINES 5000 /* max #lines to be sorted */

char *lineptr[MAXLINES]; /* pointers to text lines */

int readlines(char *lineptr[], int nlines);
void writelines(char *lineptr[], int nlines);
void qsort(char *lineptr[], int left, int right);

/* sort input lines*/
int
main(void)
{
	int nlines; /* number of input lines read */

	if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
		qsort(lineptr, 0, nlines - 1);
		writelines(lineptr, nlines);
		return 0;
	} else {
		fprintf(stderr, "error: input too big to sort\n");
		return 1;
	}
}

#define MAXLEN 1000 /* max length of input line */
int getline(char *, int);
char *alloc(int);

/* readlines: read input lines */
int readlines(char *lineptr[], int maxlines)
{
	int len, nlines;
	char *p, line[MAXLEN];

	nlines = 0;
	while ((len = getline(line, MAXLEN)) > 0)
		if (nlines >= maxlines || (p = alloc(len)) == NULL)
			return -1;
		else {
			line[len - 1] = '\0'; /* delete newline */
			strcpy(p, line);
			lineptr[nlines++] = p;
		}
	return nlines;
}

/* writelines: write output lines */
void writelines(char *lineptr[], int nlines)
{
	while (nlines-- > 0)
		printf("%s\n", *lineptr++);
}

/* qsort: sort v[left]...v[right] into increasing order */
void qsort(char *v[], int left, int right)
{
	int i, last;
	void swap(char *v[], int i, int j);

	if (left >= right)	/* do nothing if array containts */
		return;		/* fewer than two elements */
	swap(v, left, (left + right) / 2);
	last = left;
	for (i = left + 1; i <= right; i++)
		if (strcmp(v[i], v[left]) < 0)
			swap(v, ++last, i);
	swap(v, left, last);
	qsort(v, left, last - 1);
	qsort(v, last + 1, right);
}

/* swap: interchange v[i] and v[j] */
void swap(char*v[], int i, int j)
{
	char *temp;
	temp = v[i];
	v[i] = v[j];
	v[j] = temp;
}

#define ALLOCSIZE 10000 /* size of available space */

static char allocbuf[ALLOCSIZE]; /* storage for alloc */
static char *allocp = allocbuf; /* next free position */
char *alloc(int n) /* return pointer to n characters */
{
	if (allocbuf + ALLOCSIZE - allocp >= n) { /* it fits */
		allocp += n;
		return allocp - n; /* old p */
	} else { /* not enough room */
		return 0;
	}
}

void afree(char *p) /* free storage pointed to by p */
{
	if (p >= allocbuf && p < allocbuf + ALLOCSIZE)
		allocp = p;
}