exc/k&r/05-pointers-and-arrays/05-07-sort.c

#include <stdio.h>
#include <ctype.h>
#include <assert.h>

/* array bounds */
#define MAXLINES 100 
#define BUFF_SIZE (80 * MAXLINES) 

int readlines(char *lines[], int maxlines, char *ln_buff, size_t lb_size);
void writelines(char *lines[], int n);
void qsort_string(char *v[], int left, int right);

/* sorts lines from stdin and prints them */
int main()
{
    char *lines[MAXLINES]; 
    char buffer[BUFF_SIZE];
    
    int line_count = readlines(lines, MAXLINES, buffer, BUFF_SIZE);
    if (line_count < 0) {
        line_count = -line_count - 1;
        printf("warning: buffer overflow occured, read %d lines\n", line_count);
    } else if (line_count > MAXLINES) {
        line_count = MAXLINES;
        printf("warning: too many lines, read %d lines\n", line_count);
    }
    qsort_string(lines, 0, line_count-1);
    writelines(lines, line_count);
    return 0;
}

/* ---------- reading/printing functions */
#include <string.h>
/* writelines: prints n lines */
void writelines(char *lines[], int n)
{
    while (n--)
        printf("%s\n", *lines++);
}

/* readlines: reads lines from input, writing them to ln_buff
 * and line pointers to lines. 
 * returns number of lines read,
 * -lines_read-1 < 0 on buffer overflow
 * maxlines+1 on lines overflow */
int readlines(char *lines[], int maxlines, char *buffer, size_t buff_size)
{
    assert(maxlines > 0);
    char ** const fst_line = lines;
    int c, not_empty = 0;

    for (*lines = buffer; (c = getchar()) != EOF && buff_size; --buff_size) {
        not_empty |= !isspace(c);
        if (c == '\n') {
            if (!not_empty) { /* skip empty lines */
                buff_size += buffer - *lines;
                buffer = *lines;
                continue;
            }
            not_empty = 0;
            *buffer++ = '\0';
            if (!--maxlines)
                break;
            *++lines = buffer;
        } else
            *buffer++ = c; 
    }
    /* ignore trailing whitespace and empty lines */
    while (c != EOF && isspace(c))
            c = getchar();
    if (c != EOF && !buff_size) /* buffer overflow, return -lines_read-1 */
        return fst_line - lines - 1;
    if (c != EOF && !maxlines) /* lines overflow, return maxlines+1 */
        return lines - fst_line + 2;
    return lines - fst_line + not_empty;
}

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


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

    if (left >= right) /* do nothing if array contains */
        return;        /* fewer than two elements */
    swap(v, left, (left + right)/2); /* move partition elem */
    last = left; /* to v[0] */

    for (i = left+1; i <= right; i++) /* partition */
        if (strcmp(v[i], v[left]) < 0)
            swap(v, ++last, i);
    swap(v, left, last); /* restore partition elem */

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