C语言练习5

   1    #include <stdio.h>
   2    #include <string.h>
   3 
   4    #define MAXLINES 5000     /* max #lines to be sorted */
   5 
   6    char *lineptr[MAXLINES];  /* pointers to text lines */
   7 
   8    int readlines(char *lineptr[], int nlines);
   9    void writelines(char *lineptr[], int nlines);
  10 
  11    void qsort(char *lineptr[], int left, int right);
  12 
  13    /* sort input lines */
  14    main()
  15    {
  16        int nlines;     /* number of input lines read */
  17 
  18        if ((nlines = readlines(lineptr, MAXLINES)) >= 0) {
  19            qsort(lineptr, 0, nlines-1);
  20            writelines(lineptr, nlines);
  21            return 0;
  22        } else {
  23            printf("error: input too big to sort\n");
  24            return 1;
  25        }
  26    }
  27 
  28    #define MAXLEN 1000  /* max length of any input line */
  29    int getline(char *, int);
  30    char *alloc(int);
  31 
  32    /* readlines:  read input lines */
  33    int readlines(char *lineptr[], int maxlines)
  34    {
  35        int len, nlines;
  36        char *p, line[MAXLEN];
  37 
  38        nlines = 0;
  39        while ((len = getline(line, MAXLEN)) > 0)
  40            if (nlines >= maxlines || p = alloc(len) == NULL)
  41                return -1;
  42            else {
  43                line[len-1] = '\0';  /* delete newline */
  44                strcpy(p, line);
  45                lineptr[nlines++] = p;
  46            }
  47        return nlines;
  48    }
  49 
  50    /* writelines:  write output lines */
  51    void writelines(char *lineptr[], int nlines)
  52    {
  53        int i;
  54 
  55        for (i = 0; i < nlines; i++)
  56            printf("%s\n", lineptr[i]);
  57    }
  58    /* qsort:  sort v[left]...v[right] into increasing order */
  59    void qsort(char *v[], int left, int right)
  60    {
  61        int i, last;
  62        void swap(char *v[], int i, int j);
  63 
  64        if (left >= right)  /* do nothing if array contains */
  65            return;         /* fewer than two elements */
  66        swap(v, left, (left + right)/2);
  67        last = left;
  68        for (i = left+1; i <= right; i++)
  69            if (strcmp(v[i], v[left]) < 0)
  70                swap(v, ++last, i);
  71        swap(v, left, last);
  72        qsort(v, left, last-1);
  73        qsort(v, last+1, right);
  74    }
  75    /* swap:  interchange v[i] and v[j] */
  76    void swap(char *v[], int i, int j)
  77    {
  78        char *temp;
  79 
  80        temp = v[i];
  81        v[i] = v[j];
  82        v[j] = temp;
  83    }