Exercise 5.14. Modify the sort program to handle a -r flag, which indicates sorting in reverse (decreasing) order

Exercise 5.14. 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 <string.h>

#define MAXLINES 5000 //max lines to be sorted

#define BUFSIZE 5000

char *lineptr[MAXLINES];

int readlines(char *lineptr[], char *buf, int maxlines);

void writelines(char *lineptr[], int nlines, int order);

void sort(void *v[], int left, int right, 

            int (*comp) (void *, void *));

int numcmp(char *s1, char *s2);

/* sort input lines */

int main(int argc, char *argv[])

{

    int nlines; //number of input lines read

    int numeric, order; // 1 if numeric sort & order sort

    char buf[BUFSIZE];

    

    numeric = 0;

    order = 0;

    

    if(argc > 2)

    {

        if(strcmp(argv[1], "-n") == 0)

            numeric = 1;

        if(strcmp(argv[2], "-n") == 0)

                numeric = 1;

        if(strcmp(argv[1], "-r") == 0)

            order = 1;

        if(strcmp(argv[2], "-r") == 0)

                order = 1;

    } 

    if(argc > 1)

    {

        if(strcmp(argv[1], "-n") == 0)

            numeric = 1;

        if(strcmp(argv[1], "-r") == 0)

            order = 1;

    }

    if((nlines = readlines(lineptr,buf, MAXLINES)) >= 0)

    {

        sort((void **)lineptr, 0, nlines - 1, 

            (int (*) (void*, void*)) (numeric ? numcmp : strcmp));

        writelines(lineptr, nlines, order);

        return 0;

    }

    else

    {

        printf("input too big to sort\n");

        return 1;

    }

}

/* sort: sort v[left]...v[right] into increasing order */

void sort(void *v[], int left, int right,

            int (*comp) (void *, void *))

{

    int i, last;

    void swap(void *v[], int i, int j);

    

    if(left >= right) //do nothing if array contains

        return;       //fewer than two elements

    swap(v, left, (left + right)/2);

    last = left;

    for(i = left + 1; i <= right; i++)

        if((*comp) (v[i], v[left]) < 0)

            swap(v, ++last, i);

    swap(v, left, last);

    sort(v, left, last - 1, comp);

    sort(v, last + 1, right, comp);

}

#include <stdlib.h>

/* numcmp: compare s1 and s2 numericalli */

int numcmp(char *s1, 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 //max lenght of any input line

int getlin(char *, int);

/* readlines: read input lines */

int readlines(char *lineptr[], char *buf, int maxlines)

{

    int len, nlines;

    char line[MAXLEN];

    

    char *p = buf;     

    char *bufstop = buf + BUFSIZE;

    

    nlines = 0;

    while((len = getlin(line, MAXLEN)) > 0)

    {

        if(nlines >= maxlines || p + len > bufstop)

            return -1;

        else

        {

            line[len - 1] = '\0'; //delete newline

            strcpy(p, line);

            lineptr[nlines++] = p;

            p += len;

        }

    }

    return nlines;

}

/* writelines: write output lines */

void writelines(char *lineptr[], int nlines, int order)

{

    int i;

    

    printf("\n");

    if(order == 0)

        for(i = 0; i < nlines; i++)

            printf("%s\n", lineptr[i]);

    else 

        for(i = nlines-1;i >= 0; i--)

            printf("%s\n", lineptr[i]);

}

int getlin(char *l, int lim)

{

    int c;

    char *tmp = l;

    

    for(; --lim > 0 && (c=getchar()) != EOF && c!='\n'; l++)

        *l = c;

    if(c=='\n')

        *l++ = c;

    *l = '\0';

    return l - tmp;

}

Result: