Exercise 5.14

Page 121

Modify the sort program to handle a -r flag, which indicates sorting in reverse (decreasing) order. Be sure that -r works with -n.

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#define MAXLINES 5000
#define MAXCHARS 500000
char *lineptr[MAXLINES];

int readlines(char *lineptr[], int maxlines, char storage[], int maxchars);
void writelines(char *lineptr[], int nlines);

void q_sort(void *lineptr[], int left, int right,
	    int (*comp)(const char *, const char *), bool reverse);
int numcmp(const char *, const char *);

int main(int argc, char *argv[])
{
	int nlines;
	int numeric = 0;
	bool reverse = false;
	char storage[MAXCHARS];

	while (--argc > 0) {
		if (strcmp(argv[argc], "-n") == 0) {
			numeric = 1;
		} else if (strcmp(argv[argc], "-r") == 0) {
			reverse = true;
		}
	}

	if ((nlines = readlines(lineptr, MAXLINES, storage, MAXCHARS)) >= 0) {
		q_sort((void **)lineptr, 0, nlines - 1,
		       (int (*)(const char *, const char *))(numeric ? numcmp :
									     strcmp),
		       reverse);
		writelines(lineptr, nlines);
		return 0;
	} else {
		printf("input too big to sort \n");
		return 1;
	}
}

void q_sort(void *v[], int left, int right,
	    int (*comp)(const char *, const char *), bool reverse)
{
	int i, last, comp_result;
	void swap(void *v[], int, int);

	if (left >= right) {
		return;
	}
	swap(v, left, (left + right) / 2);
	last = left;
	for (i = left + 1; i <= right; i++) {
		comp_result = (*comp)(v[i], v[left]);
		if (reverse && comp_result >= 0) {
			swap(v, ++last, i);
		} else if (!reverse && comp_result < 0) {
			swap(v, ++last, i);
		}
	}
	swap(v, left, last);
	q_sort(v, left, last - 1, comp, opts);
	q_sort(v, last + 1, right, comp, opts);
}

int numcmp(const char *s1, const char *s2)
{
	double v1, v2;

	v1 = atof(s1);
	v2 = atof(s2);
	if (v1 < v2) {
		return -1;
	} else if (v1 > v2) {
		return 1;
	} else {
		return 0;
	}
}

void swap(void *v[], int i, int j)
{
	void *temp;
	temp = v[i];
	v[i] = v[j];
	v[j] = temp;
}

#define MAXLEN 1000
int get_line(char s[], int lim);
int readlines(char *lineptr[], int maxlines, char storage[], int maxchars)
{
	int len, nlines;
	char line[MAXLEN];
	int i;

	i = 0;
	nlines = 0;
	while ((len = get_line(line, MAXLEN)) > 0) {
		if (nlines >= maxlines || (i + len) >= maxchars) {
			return -1;
		} else {
			line[len - 1] = '\0';
			strcpy(storage + i, line);
			lineptr[nlines++] = storage + i;
			i += len;
		}
	}
	return nlines;
}

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

int get_line(char s[], int lim)
{
	int c, i;

	i = 0;
	while (--lim > 0 && (c = getchar()) != EOF && c != '\n') {
		s[i++] = c;
	}
	if (c == '\n') {
		s[i++] = c;
	}
	s[i] = '\0';
	return i;
}