fgetc.c

   1 /* ################################################################### */
   2 /* Copyright 2015, Pierre Gentile (p.gen.progs@gmail.com)              */
   3 /*                                                                     */
   4 /* This Source Code Form is subject to the terms of the Mozilla Public */
   5 /* License, v. 2.0. If a copy of the MPL was not distributed with this */
   6 /* file, You can obtain one at https://mozilla.org/MPL/2.0/.           */
   7 /* ################################################################### */
   8
   9 /* ************************************************************************* */
  10 /* Custom fgetc/ungetc implementation able to unget more than one character. */
  11 /* ************************************************************************* */
  12
  13 #include <stdio.h>
  14 #include "fgetc.h"
  15
  16 enum
  17 {
  18   GETC_BUFF_SIZE = 16
  19 };
  20
  21 static unsigned char getc_buffer[GETC_BUFF_SIZE] = { '\0' };
  22
  23 static long next_buffer_pos = 0; /* Next free position in the getc buffer. */
  24
  25 /* ======================================== */
  26 /* Gets a (possibly pushed-back) character. */
  27 /* ======================================== */
  28 int
  29 my_fgetc(FILE *input)
  30 {
  31   int c;
  32
  33   if (next_buffer_pos > 0)
  34     return getc_buffer[--next_buffer_pos];
  35   else
  36   {
  37     errno = 0;
  38     c     = fgetc(input);
  39
  40     while (c == EOF && errno == EAGAIN)
  41     {
  42       errno = 0;
  43       c     = fgetc(input);
  44     }
  45
  46     return c;
  47   }
  48 }
  49
  50 /* =============================== */
  51 /* Pushes character back on input. */
  52 /* =============================== */
  53 int
  54 my_ungetc(int c, FILE *input)
  55 {
  56   int rc;
  57
  58   if (next_buffer_pos >= GETC_BUFF_SIZE)
  59     rc = EOF;
  60   else
  61   {
  62     rc = getc_buffer[next_buffer_pos++] = (unsigned char)c;
  63
  64     if (feof(input))
  65       clearerr(input); /* No more EOF. */
  66   }
  67
  68   return rc;
  69 }