numlinesort#

numlinesort.c
/* Sorting program, with a provision of sorting lines numerically as well */
#include<stdio.h>
#include<string.h>
#define MAXLINES 5000 /* maximum number of lines to be sorted */
char *lineptr[MAXLINES];    /* pointers to text lines */

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

void myqsort(void *lineptr[],int left,int right,int (*comp)(void *,void *));

int numcmp(char *,char *);

/* sort input lines */

int main(int argc,char *argv[])
{
    int nlines; /* number of input lines read */
    int numeric = 0;    /* if numeric sort */

    if( argc > 1 && strcmp(argv[1],"-n") == 0)
        numeric = 1;
    if( (nlines = readlines(lineptr,MAXLINES)) >= 0)
    {
        myqsort((void **)lineptr,0,nlines -1,(int (*)(void *,void *))(numeric ? numcmp:strcmp));
        writelines(lineptr,nlines);
        return 0;
    }
    else
    {
        printf("input too big to sort \n");
        return 1;
    }
}

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

void myqsort(void *v[],int left,int right,int (*comp)(void *,void *))
{
    int i,last;
    void swap(void *v[],int,int);
    if(left >= right)   /* do nothing if array contains fewer than two elements */
        return;

    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);
    myqsort(v,left,last-1,comp);
    myqsort(v,last+1,right,comp);
}

#include<stdlib.h>

/* numcmp: compare s1 and s2 numerically */

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;
}

/* for realines and writelines */

#define MAXLEN 1000

int getline(char *,int);
char *alloc(int);

/* readlines: read input line */

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 line */

void writelines(char *lineptr[],int nlines)
{
    int i;
    for(i =0;i < nlines;i++)
        printf("%s\n",lineptr[i]);
}


/* for *alloc(int) */

#define ALLOCSIZE 10000

static char allocbuf[ALLOCSIZE];
static char *allocp = allocbuf;

char *alloc(int n)
{
    if(allocbuf + ALLOCSIZE - allocp >= n)
    {
        allocp += n;
        return allocp -n;
    }
    else
        return 0;
}

void afree(char *p)
{
    if(p >= allocbuf && p < allocbuf + ALLOCSIZE)
        allocp = p;
}



/* getline: read a line into s and return its length */

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

    for(i=0;i<lim-1 && ((c=getchar())!=EOF) && c!='\n';++i)
        s[i] =c;

    if(c == '\n')
    {
        s[i]  =c;
        ++i;
    }

    s[i] = '\0';
    
    return i;
}