krx11800.c

来自「answer of the c programming language sec」· C语言 代码 · 共 76 行

/* K&R2 1-18 p31: Write a program to remove trailing blanks and tabs
   from each line of input, and to delete entirely blank lines.

   The program specification is ambiguous: does "entirely blank lines"
   mean lines that contain no characters other than newline, or does
   it include lines composed of blanks and tabs followed by newline?
   The latter interpretation is taken here.

   This implementation does not use any features not introduced in the
   first chapter of K&R2.  As a result, it can't use pointers to
   dynamically allocate a buffer to store blanks that it has seen, so
   it must limit the number of blanks that are allowed to occur
   consecutively.  (This is the value of MAXQUEUE, minus one.)

   It is intended that this implementation "degrades gracefully."
   Even though a particular input might have 1000 or more blanks or
   tabs in a row, causing a problem for a single pass, multiple passes
   through the file will correct the problem.  The program signals the
   need for such an additional pass by returning a failure code to the
   operating system.  (EXIT_FAILURE isn't mentioned in the first
   chapter of K&R, but I'm making an exception here.) */

#include <stdio.h>
#include <stdlib.h>

#define MAXQUEUE 1001

int advance(int pointer)
{
  if (pointer < MAXQUEUE - 1)
    return pointer + 1;
  else
    return 0;
}

int main(void)
{
  char blank[MAXQUEUE];
  int head, tail;
  int nonspace;
  int retval;
  int c;

  retval = nonspace = head = tail = 0;
  while ((c = getchar()) != EOF) {
    if (c == '\n') {
      head = tail = 0;
      if (nonspace)
        putchar('\n');
      nonspace = 0;
    }
    else if (c == ' ' || c == '\t') {
      if (advance(head) == tail) {
        putchar(blank[tail]);
        tail = advance(tail);
        nonspace = 1;
        retval = EXIT_FAILURE;
      }

      blank[head] = c;
      head = advance(head);
    }
    else {
      while (head != tail) {
        putchar(blank[tail]);
        tail = advance(tail);
      }
      putchar(c);
      nonspace = 1;
    }
  }

  return retval;
}