Exercise 5-7: readlines without alloc

Rewrite readlines to store lines in an array supplied by main, rather than calling alloc to maintain storage. How much faster is the program?

#define MAXLEN 1000  /* max length of any input line */
int getline(char *, int);
char *alloc(int);

/* readlines:  read input lines */
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;
}

Use it in the sort program of Section 5.6, which prints its input lines in increasing order as strcmp compares them. The input is at most 5000 lines of at most 1000 characters each, 50,000 characters in all, and its last line may have no newline.