hello,
i am developing a c coding for comparing two txt files(one key file with the transcripted or duplicete file) to figure out the wrong text in the transcripted file.Can anyone help me that how to develop the codes.

>>Can anyone help me that how to develop the codes.

Sure thing -- start here

#include <stdio.h>

int main()
{
    // put your code here
}

here, try this... just remove the comments, change some variable names, sign it and turn it in. trust me, it works. you'll get an "A" for sure.

/* diff - compare files line by line

   Copyright (C) 1988, 1989, 1992, 1993, 1994, 1996, 1998, 2001, 2002,
   2004 Free Software Foundation, Inc.

   This file is part of GNU DIFF.

   GNU DIFF is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   GNU DIFF is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
   See the GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with GNU DIFF; see the file COPYING.
   If not, write to the Free Software Foundation,
   59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.  */

#define GDIFF_MAIN
#include "diff.h"
#include "paths.h"
#include <c-stack.h>
#include <dirname.h>
#include <error.h>
#include <exclude.h>
#include <exit.h>
#include <exitfail.h>
#include <file-type.h>
#include <fnmatch.h>
#include <getopt.h>
#include <hard-locale.h>
#include <posixver.h>
#include <prepargs.h>
#include <quotesys.h>
#include <setmode.h>
#include <version-etc.h>
#include <xalloc.h>

#ifndef GUTTER_WIDTH_MINIMUM
# define GUTTER_WIDTH_MINIMUM 3
#endif

struct regexp_list
{
  char *regexps;	/* chars representing disjunction of the regexps */
  size_t len;		/* chars used in `regexps' */
  size_t size;		/* size malloc'ed for `regexps'; 0 if not malloc'ed */
  bool multiple_regexps;/* Does `regexps' represent a disjunction?  */
  struct re_pattern_buffer *buf;
};

static int compare_files (struct comparison const *, char const *, char const *);
static void add_regexp (struct regexp_list *, char const *);
static void summarize_regexp_list (struct regexp_list *);
static void specify_style (enum output_style);
static void specify_value (char const **, char const *, char const *);
static void try_help (char const *, char const *) __attribute__((noreturn));
static void check_stdout (void);
static void usage (void);

/* If comparing directories, compare their common subdirectories
   recursively.  */
static bool recursive;

/* In context diffs, show previous lines that match these regexps.  */
static struct regexp_list function_regexp_list;

/* Ignore changes affecting only lines that match these regexps.  */
static struct regexp_list ignore_regexp_list;

#if HAVE_SETMODE_DOS
/* Use binary I/O when reading and writing data (--binary).
   On POSIX hosts, this has no effect.  */
static bool binary;
#else
enum { binary = true };
#endif

/* When comparing directories, if a file appears only in one
   directory, treat it as present but empty in the other (-N).
   Then `patch' would create the file with appropriate contents.  */
static bool new_file;

/* When comparing directories, if a file appears only in the second
   directory of the two, treat it as present but empty in the other
   (--unidirectional-new-file).
   Then `patch' would create the file with appropriate contents.  */
static bool unidirectional_new_file;

/* Report files compared that are the same (-s).
   Normally nothing is output when that happens.  */
static bool report_identical_files;


/* Return a string containing the command options with which diff was invoked.
   Spaces appear between what were separate ARGV-elements.
   There is a space at the beginning but none at the end.
   If there were no options, the result is an empty string.

   Arguments: OPTIONVEC, a vector containing separate ARGV-elements, and COUNT,
   the length of that vector.  */

static char *
option_list (char **optionvec, int count)
{
  int i;
  size_t size = 1;
  char *result;
  char *p;

  for (i = 0; i < count; i++)
    size += 1 + quote_system_arg ((char *) 0, optionvec[i]);

  p = result = xmalloc (size);

  for (i = 0; i < count; i++)
    {
      *p++ = ' ';
      p += quote_system_arg (p, optionvec[i]);
    }

  *p = 0;
  return result;
}


/* Return an option value suitable for add_exclude.  */

static int
exclude_options (void)
{
  return EXCLUDE_WILDCARDS | (ignore_file_name_case ? FNM_CASEFOLD : 0);
}

static char const shortopts[] =
"0123456789abBcC:dD:eEfF:hHiI:lL:nNpPqrsS:tTuU:vwW:x:X:y";

/* Values for long options that do not have single-letter equivalents.  */
enum
{
  BINARY_OPTION = CHAR_MAX + 1,
  FROM_FILE_OPTION,
  HELP_OPTION,
  HORIZON_LINES_OPTION,
  IGNORE_FILE_NAME_CASE_OPTION,
  INHIBIT_HUNK_MERGE_OPTION,
  LEFT_COLUMN_OPTION,
  LINE_FORMAT_OPTION,
  NO_IGNORE_FILE_NAME_CASE_OPTION,
  NORMAL_OPTION,
  SDIFF_MERGE_ASSIST_OPTION,
  STRIP_TRAILING_CR_OPTION,
  SUPPRESS_COMMON_LINES_OPTION,
  TABSIZE_OPTION,
  TO_FILE_OPTION,

  /* These options must be in sequence.  */
  UNCHANGED_LINE_FORMAT_OPTION,
  OLD_LINE_FORMAT_OPTION,
  NEW_LINE_FORMAT_OPTION,

  /* These options must be in sequence.  */
  UNCHANGED_GROUP_FORMAT_OPTION,
  OLD_GROUP_FORMAT_OPTION,
  NEW_GROUP_FORMAT_OPTION,
  CHANGED_GROUP_FORMAT_OPTION
};

static char const group_format_option[][sizeof "--unchanged-group-format"] =
  {
    "--unchanged-group-format",
    "--old-group-format",
    "--new-group-format",
    "--changed-group-format"
  };

static char const line_format_option[][sizeof "--unchanged-line-format"] =
  {
    "--unchanged-line-format",
    "--old-line-format",
    "--new-line-format"
  };

static struct option const longopts[] =
{
  {"binary", 0, 0, BINARY_OPTION},
  {"brief", 0, 0, 'q'},
  {"changed-group-format", 1, 0, CHANGED_GROUP_FORMAT_OPTION},
  {"context", 2, 0, 'C'},
  {"ed", 0, 0, 'e'},
  {"exclude", 1, 0, 'x'},
  {"exclude-from", 1, 0, 'X'},
  {"expand-tabs", 0, 0, 't'},
  {"forward-ed", 0, 0, 'f'},
  {"from-file", 1, 0, FROM_FILE_OPTION},
  {"help", 0, 0, HELP_OPTION},
  {"horizon-lines", 1, 0, HORIZON_LINES_OPTION},
  {"ifdef", 1, 0, 'D'},
  {"ignore-all-space", 0, 0, 'w'},
  {"ignore-blank-lines", 0, 0, 'B'},
  {"ignore-case", 0, 0, 'i'},
  {"ignore-file-name-case", 0, 0, IGNORE_FILE_NAME_CASE_OPTION},
  {"ignore-matching-lines", 1, 0, 'I'},
  {"ignore-space-change", 0, 0, 'b'},
  {"ignore-tab-expansion", 0, 0, 'E'},
  {"inhibit-hunk-merge", 0, 0, INHIBIT_HUNK_MERGE_OPTION},
  {"initial-tab", 0, 0, 'T'},
  {"label", 1, 0, 'L'},
  {"left-column", 0, 0, LEFT_COLUMN_OPTION},
  {"line-format", 1, 0, LINE_FORMAT_OPTION},
  {"minimal", 0, 0, 'd'},
  {"new-file", 0, 0, 'N'},
  {"new-group-format", 1, 0, NEW_GROUP_FORMAT_OPTION},
  {"new-line-format", 1, 0, NEW_LINE_FORMAT_OPTION},
  {"no-ignore-file-name-case", 0, 0, NO_IGNORE_FILE_NAME_CASE_OPTION},
  {"normal", 0, 0, NORMAL_OPTION},
  {"old-group-format", 1, 0, OLD_GROUP_FORMAT_OPTION},
  {"old-line-format", 1, 0, OLD_LINE_FORMAT_OPTION},
  {"paginate", 0, 0, 'l'},
  {"rcs", 0, 0, 'n'},
  {"recursive", 0, 0, 'r'},
  {"report-identical-files", 0, 0, 's'},
  {"sdiff-merge-assist", 0, 0, SDIFF_MERGE_ASSIST_OPTION},
  {"show-c-function", 0, 0, 'p'},
  {"show-function-line", 1, 0, 'F'},
  {"side-by-side", 0, 0, 'y'},
  {"speed-large-files", 0, 0, 'H'},
  {"starting-file", 1, 0, 'S'},
  {"strip-trailing-cr", 0, 0, STRIP_TRAILING_CR_OPTION},
  {"suppress-common-lines", 0, 0, SUPPRESS_COMMON_LINES_OPTION},
  {"tabsize", 1, 0, TABSIZE_OPTION},
  {"text", 0, 0, 'a'},
  {"to-file", 1, 0, TO_FILE_OPTION},
  {"unchanged-group-format", 1, 0, UNCHANGED_GROUP_FORMAT_OPTION},
  {"unchanged-line-format", 1, 0, UNCHANGED_LINE_FORMAT_OPTION},
  {"unidirectional-new-file", 0, 0, 'P'},
  {"unified", 2, 0, 'U'},
  {"version", 0, 0, 'v'},
  {"width", 1, 0, 'W'},
  {0, 0, 0, 0}
};

int
main (int argc, char **argv)
{
  int exit_status = EXIT_SUCCESS;
  int c;
  int i;
  int prev = -1;
  lin ocontext = -1;
  bool explicit_context = false;
  size_t width = 0;
  bool show_c_function = false;
  char const *from_file = 0;
  char const *to_file = 0;
  uintmax_t numval;
  char *numend;

  /* Do our initializations.  */
  exit_failure = 2;
  initialize_main (&argc, &argv);
  program_name = argv[0];
  setlocale (LC_ALL, "");
  bindtextdomain (PACKAGE, LOCALEDIR);
  textdomain (PACKAGE);
  c_stack_action (0);
  function_regexp_list.buf = &function_regexp;
  ignore_regexp_list.buf = &ignore_regexp;
  re_set_syntax (RE_SYNTAX_GREP | RE_NO_POSIX_BACKTRACKING);
  excluded = new_exclude ();

  /* Decode the options.  */

  while ((c = getopt_long (argc, argv, shortopts, longopts, 0)) != -1)
    {
      switch (c)
	{
	case 0:
	  break;

	case '0':
	case '1':
	case '2':
	case '3':
	case '4':
	case '5':
	case '6':
	case '7':
	case '8':
	case '9':
	  if (! ISDIGIT (prev))
	    ocontext = c - '0';
	  else if (LIN_MAX / 10 < ocontext
		   || ((ocontext = 10 * ocontext + c - '0') < 0))
	    ocontext = LIN_MAX;
	  break;

	case 'a':
	  text = true;
	  break;

	case 'b':
	  if (ignore_white_space < IGNORE_SPACE_CHANGE)
	    ignore_white_space = IGNORE_SPACE_CHANGE;
	  break;

	case 'B':
	  ignore_blank_lines = true;
	  break;

	case 'C':
	case 'U':
	  {
	    if (optarg)
	      {
		numval = strtoumax (optarg, &numend, 10);
		if (*numend)
		  try_help ("invalid context length `%s'", optarg);
		if (LIN_MAX < numval)
		  numval = LIN_MAX;
	      }
	    else
	      numval = 3;

	    specify_style (c == 'U' ? OUTPUT_UNIFIED : OUTPUT_CONTEXT);
	    if (context < numval)
	      context = numval;
	    explicit_context = true;
	  }
	  break;

	case 'c':
	  specify_style (OUTPUT_CONTEXT);
	  if (context < 3)
	    context = 3;
	  break;

	case 'd':
	  minimal = true;
	  break;

	case 'D':
	  specify_style (OUTPUT_IFDEF);
	  {
	    static char const C_ifdef_group_formats[] =
	      "%%=%c#ifndef %s\n%%<#endif /* ! %s */\n%c#ifdef %s\n%%>#endif /* %s */\n%c#ifndef %s\n%%<#else /* %s */\n%%>#endif /* %s */\n";
	    char *b = xmalloc (sizeof C_ifdef_group_formats
			       + 7 * strlen (optarg) - 14 /* 7*"%s" */
			       - 8 /* 5*"%%" + 3*"%c" */);
	    sprintf (b, C_ifdef_group_formats,
		     0,
		     optarg, optarg, 0,
		     optarg, optarg, 0,
		     optarg, optarg, optarg);
	    for (i = 0; i < sizeof group_format / sizeof *group_format; i++)
	      {
		specify_value (&group_format[i], b, "-D");
		b += strlen (b) + 1;
	      }
	  }
	  break;

	case 'e':
	  specify_style (OUTPUT_ED);
	  break;

	case 'E':
	  if (ignore_white_space < IGNORE_TAB_EXPANSION)
	    ignore_white_space = IGNORE_TAB_EXPANSION;
	  break;

	case 'f':
	  specify_style (OUTPUT_FORWARD_ED);
	  break;

	case 'F':
	  add_regexp (&function_regexp_list, optarg);
	  break;

	case 'h':
	  /* Split the files into chunks for faster processing.
	     Usually does not change the result.

	     This currently has no effect.  */
	  break;

	case 'H':
	  speed_large_files = true;
	  break;

	case 'i':
	  ignore_case = true;
	  break;

	case 'I':
	  add_regexp (&ignore_regexp_list, optarg);
	  break;

	case 'l':
	  if (!pr_program[0])
	    try_help ("pagination not supported on this host", 0);
	  paginate = true;
#ifdef SIGCHLD
	  /* Pagination requires forking and waiting, and
	     System V fork+wait does not work if SIGCHLD is ignored.  */
	  signal (SIGCHLD, SIG_DFL);
#endif
	  break;

	case 'L':
	  if (!file_label[0])
	    file_label[0] = optarg;
	  else if (!file_label[1])
	    file_label[1] = optarg;
	  else
	    fatal ("too many file label options");
	  break;

	case 'n':
	  specify_style (OUTPUT_RCS);
	  break;

	case 'N':
	  new_file = true;
	  break;

	case 'p':
	  show_c_function = true;
	  add_regexp (&function_regexp_list, "^[[:alpha:]$_]");
	  break;

	case 'P':
	  unidirectional_new_file = true;
	  break;

	case 'q':
	  brief = true;
	  break;

	case 'r':
	  recursive = true;
	  break;

	case 's':
	  report_identical_files = true;
	  break;

	case 'S':
	  specify_value (&starting_file, optarg, "-S");
	  break;

	case 't':
	  expand_tabs = true;
	  break;

	case 'T':
	  initial_tab = true;
	  break;

	case 'u':
	  specify_style (OUTPUT_UNIFIED);
	  if (context < 3)
	    context = 3;
	  break;

	case 'v':
	  version_etc (stdout, "diff", PACKAGE_NAME, PACKAGE_VERSION,
		       "Paul Eggert", "Mike Haertel", "David Hayes",
		       "Richard Stallman", "Len Tower", (char *) 0);
	  check_stdout ();
	  return EXIT_SUCCESS;

	case 'w':
	  ignore_white_space = IGNORE_ALL_SPACE;
	  break;

	case 'x':
	  add_exclude (excluded, optarg, exclude_options ());
	  break;

	case 'X':
	  if (add_exclude_file (add_exclude, excluded, optarg,
				exclude_options (), '\n'))
	    pfatal_with_name (optarg);
	  break;

	case 'y':
	  specify_style (OUTPUT_SDIFF);
	  break;

	case 'W':
	  numval = strtoumax (optarg, &numend, 10);
	  if (! (0 < numval && numval <= SIZE_MAX) || *numend)
	    try_help ("invalid width `%s'", optarg);
	  if (width != numval)
	    {
	      if (width)
		fatal ("conflicting width options");
	      width = numval;
	    }
	  break;

	case BINARY_OPTION:
#if HAVE_SETMODE_DOS
	  binary = true;
	  set_binary_mode (STDOUT_FILENO, true);
#endif
	  break;

	case FROM_FILE_OPTION:
	  specify_value (&from_file, optarg, "--from-file");
	  break;

	case HELP_OPTION:
	  usage ();
	  check_stdout ();
	  return EXIT_SUCCESS;

	case HORIZON_LINES_OPTION:
	  numval = strtoumax (optarg, &numend, 10);
	  if (*numend)
	    try_help ("invalid horizon length `%s'", optarg);
	  horizon_lines = MAX (horizon_lines, MIN (numval, LIN_MAX));
	  break;

	case IGNORE_FILE_NAME_CASE_OPTION:
	  ignore_file_name_case = true;
	  break;

	case INHIBIT_HUNK_MERGE_OPTION:
	  /* This option is obsolete, but accept it for backward
             compatibility.  */
	  break;

	case LEFT_COLUMN_OPTION:
	  left_column = true;
	  break;

	case LINE_FORMAT_OPTION:
	  specify_style (OUTPUT_IFDEF);
	  for (i = 0; i < sizeof line_format / sizeof *line_format; i++)
	    specify_value (&line_format[i], optarg, "--line-format");
	  break;

	case NO_IGNORE_FILE_NAME_CASE_OPTION:
	  ignore_file_name_case = false;
	  break;

	case NORMAL_OPTION:
	  specify_style (OUTPUT_NORMAL);
	  break;

	case SDIFF_MERGE_ASSIST_OPTION:
	  specify_style (OUTPUT_SDIFF);
	  sdiff_merge_assist = true;
	  break;

	case STRIP_TRAILING_CR_OPTION:
	  strip_trailing_cr = true;
	  break;

	case SUPPRESS_COMMON_LINES_OPTION:
	  suppress_common_lines = true;
	  break;

	case TABSIZE_OPTION:
	  numval = strtoumax (optarg, &numend, 10);
	  if (! (0 < numval && numval <= SIZE_MAX) || *numend)
	    try_help ("invalid tabsize `%s'", optarg);
	  if (tabsize != numval)
	    {
	      if (tabsize)
		fatal ("conflicting tabsize options");
	      tabsize = numval;
	    }
	  break;

	case TO_FILE_OPTION:
	  specify_value (&to_file, optarg, "--to-file");
	  break;

	case UNCHANGED_LINE_FORMAT_OPTION:
	case OLD_LINE_FORMAT_OPTION:
	case NEW_LINE_FORMAT_OPTION:
	  specify_style (OUTPUT_IFDEF);
	  c -= UNCHANGED_LINE_FORMAT_OPTION;
	  specify_value (&line_format[c], optarg, line_format_option[c]);
	  break;

	case UNCHANGED_GROUP_FORMAT_OPTION:
	case OLD_GROUP_FORMAT_OPTION:
	case NEW_GROUP_FORMAT_OPTION:
	case CHANGED_GROUP_FORMAT_OPTION:
	  specify_style (OUTPUT_IFDEF);
	  c -= UNCHANGED_GROUP_FORMAT_OPTION;
	  specify_value (&group_format[c], optarg, group_format_option[c]);
	  break;

	default:
	  try_help (0, 0);
	}
      prev = c;
    }

  if (output_style == OUTPUT_UNSPECIFIED)
    {
      if (show_c_function)
	{
	  specify_style (OUTPUT_CONTEXT);
	  if (ocontext < 0)
	    context = 3;
	}
      else
	specify_style (OUTPUT_NORMAL);
    }

  if (output_style != OUTPUT_CONTEXT || hard_locale (LC_TIME))
    {
#ifdef ST_MTIM_NSEC
      time_format = "%Y-%m-%d %H:%M:%S.%N %z";
#else
      time_format = "%Y-%m-%d %H:%M:%S %z";
#endif
    }
  else
    {
      /* See POSIX 1003.1-2001 for this format.  */
      time_format = "%a %b %e %T %Y";
    }

  if (0 <= ocontext)
    {
      bool modern_usage = 200112 <= posix2_version ();

      if ((output_style == OUTPUT_CONTEXT
	   || output_style == OUTPUT_UNIFIED)
	  && (context < ocontext
	      || (ocontext < context && ! explicit_context)))
	{
	  if (modern_usage)
	    {
	      error (0, 0,
		     _("`-%ld' option is obsolete; use `-%c %ld'"),
		     (long int) ocontext,
		     output_style == OUTPUT_CONTEXT ? 'C' : 'U',
		     (long int) ocontext);
	      try_help (0, 0);
	    }
	  context = ocontext;
	}
      else
	{
	  if (modern_usage)
	    {
	      error (0, 0, _("`-%ld' option is obsolete; omit it"),
		     (long int) ocontext);
	      try_help (0, 0);
	    }
	}
    }

  if (! tabsize)
    tabsize = 8;
  if (! width)
    width = 130;

  {
    /* Maximize first the half line width, and then the gutter width,
       according to the following constraints:

	1.  Two half lines plus a gutter must fit in a line.
	2.  If the half line width is nonzero:
	    a.  The gutter width is at least GUTTER_WIDTH_MINIMUM.
	    b.  If tabs are not expanded to spaces,
		a half line plus a gutter is an integral number of tabs,
		so that tabs in the right column line up.  */

    intmax_t t = expand_tabs ? 1 : tabsize;
    intmax_t w = width;
    intmax_t off = (w + t + GUTTER_WIDTH_MINIMUM) / (2 * t)  *  t;
    sdiff_half_width = MAX (0, MIN (off - GUTTER_WIDTH_MINIMUM, w - off)),
    sdiff_column2_offset = sdiff_half_width ? off : w;
  }

  /* Make the horizon at least as large as the context, so that
     shift_boundaries has more freedom to shift the first and last hunks.  */
  if (horizon_lines < context)
    horizon_lines = context;

  summarize_regexp_list (&function_regexp_list);
  summarize_regexp_list (&ignore_regexp_list);

  if (output_style == OUTPUT_IFDEF)
    {
      for (i = 0; i < sizeof line_format / sizeof *line_format; i++)
	if (!line_format[i])
	  line_format[i] = "%l\n";
      if (!group_format[OLD])
	group_format[OLD]
	  = group_format[CHANGED] ? group_format[CHANGED] : "%<";
      if (!group_format[NEW])
	group_format[NEW]
	  = group_format[CHANGED] ? group_format[CHANGED] : "%>";
      if (!group_format[UNCHANGED])
	group_format[UNCHANGED] = "%=";
      if (!group_format[CHANGED])
	group_format[CHANGED] = concat (group_format[OLD],
					group_format[NEW], "");
    }

  no_diff_means_no_output =
    (output_style == OUTPUT_IFDEF ?
      (!*group_format[UNCHANGED]
       || (strcmp (group_format[UNCHANGED], "%=") == 0
	   && !*line_format[UNCHANGED]))
     : (output_style != OUTPUT_SDIFF) | suppress_common_lines);

  files_can_be_treated_as_binary =
    (brief & binary
     & ~ (ignore_blank_lines | ignore_case | strip_trailing_cr
	  | (ignore_regexp_list.regexps || ignore_white_space)));

  switch_string = option_list (argv + 1, optind - 1);

  if (from_file)
    {
      if (to_file)
	fatal ("--from-file and --to-file both specified");
      else
	for (; optind < argc; optind++)
	  {
	    int status = compare_files ((struct comparison *) 0,
					from_file, argv[optind]);
	    if (exit_status < status)
	      exit_status = status;
	  }
    }
  else
    {
      if (to_file)
	for (; optind < argc; optind++)
	  {
	    int status = compare_files ((struct comparison *) 0,
					argv[optind], to_file);
	    if (exit_status < status)
	      exit_status = status;
	  }
      else
	{
	  if (argc - optind != 2)
	    {
	      if (argc - optind < 2)
		try_help ("missing operand after `%s'", argv[argc - 1]);
	      else
		try_help ("extra operand `%s'", argv[optind + 2]);
	    }

	  exit_status = compare_files ((struct comparison *) 0,
				       argv[optind], argv[optind + 1]);
	}
    }

  /* Print any messages that were saved up for last.  */
  print_message_queue ();

  check_stdout ();
  exit (exit_status);
  return exit_status;
}

/* Append to REGLIST the regexp PATTERN.  */

static void
add_regexp (struct regexp_list *reglist, char const *pattern)
{
  size_t patlen = strlen (pattern);
  char const *m = re_compile_pattern (pattern, patlen, reglist->buf);

  if (m != 0)
    error (0, 0, "%s: %s", pattern, m);
  else
    {
      char *regexps = reglist->regexps;
      size_t len = reglist->len;
      bool multiple_regexps = reglist->multiple_regexps = regexps != 0;
      size_t newlen = reglist->len = len + 2 * multiple_regexps + patlen;
      size_t size = reglist->size;

      if (size <= newlen)
	{
	  if (!size)
	    size = 1;

	  do size *= 2;
	  while (size <= newlen);

	  reglist->size = size;
	  reglist->regexps = regexps = xrealloc (regexps, size);
	}
      if (multiple_regexps)
	{
	  regexps[len++] = '\\';
	  regexps[len++] = '|';
	}
      memcpy (regexps + len, pattern, patlen + 1);
    }
}

/* Ensure that REGLIST represents the disjunction of its regexps.
   This is done here, rather than earlier, to avoid O(N^2) behavior.  */

static void
summarize_regexp_list (struct regexp_list *reglist)
{
  if (reglist->regexps)
    {
      /* At least one regexp was specified.  Allocate a fastmap for it.  */
      reglist->buf->fastmap = xmalloc (1 << CHAR_BIT);
      if (reglist->multiple_regexps)
	{
	  /* Compile the disjunction of the regexps.
	     (If just one regexp was specified, it is already compiled.)  */
	  char const *m = re_compile_pattern (reglist->regexps, reglist->len,
					      reglist->buf);
	  if (m != 0)
	    error (EXIT_TROUBLE, 0, "%s: %s", reglist->regexps, m);
	}
    }
}

static void
try_help (char const *reason_msgid, char const *operand)
{
  if (reason_msgid)
    error (0, 0, _(reason_msgid), operand);
  error (EXIT_TROUBLE, 0, _("Try `%s --help' for more information."),
	 program_name);
  abort ();
}

static void
check_stdout (void)
{
  if (ferror (stdout))
    fatal ("write failed");
  else if (fclose (stdout) != 0)
    pfatal_with_name (_("standard output"));
}

static char const * const option_help_msgid[] = {
  N_("Compare files line by line."),
  "",
  N_("-i  --ignore-case  Ignore case differences in file contents."),
  N_("--ignore-file-name-case  Ignore case when comparing file names."),
  N_("--no-ignore-file-name-case  Consider case when comparing file names."),
  N_("-E  --ignore-tab-expansion  Ignore changes due to tab expansion."),
  N_("-b  --ignore-space-change  Ignore changes in the amount of white space."),
  N_("-w  --ignore-all-space  Ignore all white space."),
  N_("-B  --ignore-blank-lines  Ignore changes whose lines are all blank."),
  N_("-I RE  --ignore-matching-lines=RE  Ignore changes whose lines all match RE."),
  N_("--strip-trailing-cr  Strip trailing carriage return on input."),
#if HAVE_SETMODE_DOS
  N_("--binary  Read and write data in binary mode."),
#endif
  N_("-a  --text  Treat all files as text."),
  "",
  N_("-c  -C NUM  --context[=NUM]  Output NUM (default 3) lines of copied context.\n\
-u  -U NUM  --unified[=NUM]  Output NUM (default 3) lines of unified context.\n\
  --label LABEL  Use LABEL instead of file name.\n\
  -p  --show-c-function  Show which C function each change is in.\n\
  -F RE  --show-function-line=RE  Show the most recent line matching RE."),
  N_("-q  --brief  Output only whether files differ."),
  N_("-e  --ed  Output an ed script."),
  N_("--normal  Output a normal diff."),
  N_("-n  --rcs  Output an RCS format diff."),
  N_("-y  --side-by-side  Output in two columns.\n\
  -W NUM  --width=NUM  Output at most NUM (default 130) print columns.\n\
  --left-column  Output only the left column of common lines.\n\
  --suppress-common-lines  Do not output common lines."),
  N_("-D NAME  --ifdef=NAME  Output merged file to show `#ifdef NAME' diffs."),
  N_("--GTYPE-group-format=GFMT  Similar, but format GTYPE input groups with GFMT."),
  N_("--line-format=LFMT  Similar, but format all input lines with LFMT."),
  N_("--LTYPE-line-format=LFMT  Similar, but format LTYPE input lines with LFMT."),
  N_("  LTYPE is `old', `new', or `unchanged'.  GTYPE is LTYPE or `changed'."),
  N_("  GFMT may contain:\n\
    %<  lines from FILE1\n\
    %>  lines from FILE2\n\
    %=  lines common to FILE1 and FILE2\n\
    %[-][WIDTH][.[PREC]]{doxX}LETTER  printf-style spec for LETTER\n\
      LETTERs are as follows for new group, lower case for old group:\n\
        F  first line number\n\
        L  last line number\n\
        N  number of lines = L-F+1\n\
        E  F-1\n\
        M  L+1"),
  N_("  LFMT may contain:\n\
    %L  contents of line\n\
    %l  contents of line, excluding any trailing newline\n\
    %[-][WIDTH][.[PREC]]{doxX}n  printf-style spec for input line number"),
  N_("  Either GFMT or LFMT may contain:\n\
    %%  %\n\
    %c'C'  the single character C\n\
    %c'\\OOO'  the character with octal code OOO"),
  "",
  N_("-l  --paginate  Pass the output through `pr' to paginate it."),
  N_("-t  --expand-tabs  Expand tabs to spaces in output."),
  N_("-T  --initial-tab  Make tabs line up by prepending a tab."),
  N_("--tabsize=NUM  Tab stops are every NUM (default 8) print columns."),
  "",
  N_("-r  --recursive  Recursively compare any subdirectories found."),
  N_("-N  --new-file  Treat absent files as empty."),
  N_("--unidirectional-new-file  Treat absent first files as empty."),
  N_("-s  --report-identical-files  Report when two files are the same."),
  N_("-x PAT  --exclude=PAT  Exclude files that match PAT."),
  N_("-X FILE  --exclude-from=FILE  Exclude files that match any pattern in FILE."),
  N_("-S FILE  --starting-file=FILE  Start with FILE when comparing directories."),
  N_("--from-file=FILE1  Compare FILE1 to all operands.  FILE1 can be a directory."),
  N_("--to-file=FILE2  Compare all operands to FILE2.  FILE2 can be a directory."),
  "",
  N_("--horizon-lines=NUM  Keep NUM lines of the common prefix and suffix."),
  N_("-d  --minimal  Try hard to find a smaller set of changes."),
  N_("--speed-large-files  Assume large files and many scattered small changes."),
  "",
  N_("-v  --version  Output version info."),
  N_("--help  Output this help."),
  "",
  N_("FILES are `FILE1 FILE2' or `DIR1 DIR2' or `DIR FILE...' or `FILE... DIR'."),
  N_("If --from-file or --to-file is given, there are no restrictions on FILES."),
  N_("If a FILE is `-', read standard input."),
  N_("Exit status is 0 if inputs are the same, 1 if different, 2 if trouble."),
  "",
  N_("Report bugs to <bug-gnu-utils@gnu.org>."),
  0
};

static void
usage (void)
{
  char const * const *p;

  printf (_("Usage: %s [OPTION]... FILES\n"), program_name);

  for (p = option_help_msgid;  *p;  p++)
    {
      if (!**p)
	putchar ('\n');
      else
	{
	  char const *msg = _(*p);
	  char const *nl;
	  while ((nl = strchr (msg, '\n')))
	    {
	      int msglen = nl + 1 - msg;
	      printf ("  %.*s", msglen, msg);
	      msg = nl + 1;
	    }

	  printf ("  %s\n" + 2 * (*msg != ' ' && *msg != '-'), msg);
	}
    }
}

/* Set VAR to VALUE, reporting an OPTION error if this is a
   conflict.  */
static void
specify_value (char const **var, char const *value, char const *option)
{
  if (*var && strcmp (*var, value) != 0)
    {
      error (0, 0, _("conflicting %s option value `%s'"), option, value);
      try_help (0, 0);
    }
  *var = value;
}

/* Set the output style to STYLE, diagnosing conflicts.  */
static void
specify_style (enum output_style style)
{
  if (output_style != style)
    {
      if (output_style != OUTPUT_UNSPECIFIED)
	try_help ("conflicting output style options", 0);
      output_style = style;
    }
}

/* Set the last-modified time of *ST to be the current time.  */

static void
set_mtime_to_now (struct stat *st)
{
#ifdef ST_MTIM_NSEC

# if HAVE_CLOCK_GETTIME && defined CLOCK_REALTIME
  if (clock_gettime (CLOCK_REALTIME, &st->st_mtim) == 0)
    return;
# endif

# if HAVE_GETTIMEOFDAY
  {
    struct timeval timeval;
    if (gettimeofday (&timeval, 0) == 0)
      {
	st->st_mtime = timeval.tv_sec;
	st->st_mtim.ST_MTIM_NSEC = timeval.tv_usec * 1000;
	return;
      }
  }
# endif

#endif /* ST_MTIM_NSEC */

  time (&st->st_mtime);
}

/* Compare two files (or dirs) with parent comparison PARENT
   and names NAME0 and NAME1.
   (If PARENT is 0, then the first name is just NAME0, etc.)
   This is self-contained; it opens the files and closes them.

   Value is EXIT_SUCCESS if files are the same, EXIT_FAILURE if
   different, EXIT_TROUBLE if there is a problem opening them.  */

static int
compare_files (struct comparison const *parent,
	       char const *name0,
	       char const *name1)
{
  struct comparison cmp;
#define DIR_P(f) (S_ISDIR (cmp.file[f].stat.st_mode) != 0)
  register int f;
  int status = EXIT_SUCCESS;
  bool same_files;
  char *free0, *free1;

  /* If this is directory comparison, perhaps we have a file
     that exists only in one of the directories.
     If so, just print a message to that effect.  */

  if (! ((name0 && name1)
	 || (unidirectional_new_file && name1)
	 || new_file))
    {
      char const *name = name0 == 0 ? name1 : name0;
      char const *dir = parent->file[name0 == 0].name;

      /* See POSIX 1003.1-2001 for this format.  */
      message ("Only in %s: %s\n", dir, name);

      /* Return EXIT_FAILURE so that diff_dirs will return
	 EXIT_FAILURE ("some files differ").  */
      return EXIT_FAILURE;
    }

  memset (cmp.file, 0, sizeof cmp.file);
  cmp.parent = parent;

  /* cmp.file[f].desc markers */
#define NONEXISTENT (-1) /* nonexistent file */
#define UNOPENED (-2) /* unopened file (e.g. directory) */
#define ERRNO_ENCODE(errno) (-3 - (errno)) /* encoded errno value */

#define ERRNO_DECODE(desc) (-3 - (desc)) /* inverse of ERRNO_ENCODE */

  cmp.file[0].desc = name0 == 0 ? NONEXISTENT : UNOPENED;
  cmp.file[1].desc = name1 == 0 ? NONEXISTENT : UNOPENED;

  /* Now record the full name of each file, including nonexistent ones.  */

  if (name0 == 0)
    name0 = name1;
  if (name1 == 0)
    name1 = name0;

  if (!parent)
    {
      free0 = 0;
      free1 = 0;
      cmp.file[0].name = name0;
      cmp.file[1].name = name1;
    }
  else
    {
      cmp.file[0].name = free0
	= dir_file_pathname (parent->file[0].name, name0);
      cmp.file[1].name = free1
	= dir_file_pathname (parent->file[1].name, name1);
    }

  /* Stat the files.  */

  for (f = 0; f < 2; f++)
    {
      if (cmp.file[f].desc != NONEXISTENT)
	{
	  if (f && file_name_cmp (cmp.file[f].name, cmp.file[0].name) == 0)
	    {
	      cmp.file[f].desc = cmp.file[0].desc;
	      cmp.file[f].stat = cmp.file[0].stat;
	    }
	  else if (strcmp (cmp.file[f].name, "-") == 0)
	    {
	      cmp.file[f].desc = STDIN_FILENO;
	      if (fstat (STDIN_FILENO, &cmp.file[f].stat) != 0)
		cmp.file[f].desc = ERRNO_ENCODE (errno);
	      else
		{
		  if (S_ISREG (cmp.file[f].stat.st_mode))
		    {
		      off_t pos = lseek (STDIN_FILENO, (off_t) 0, SEEK_CUR);
		      if (pos < 0)
			cmp.file[f].desc = ERRNO_ENCODE (errno);
		      else
			cmp.file[f].stat.st_size =
			  MAX (0, cmp.file[f].stat.st_size - pos);
		    }

		  /* POSIX 1003.1-2001 requires current time for
		     stdin.  */
		  set_mtime_to_now (&cmp.file[f].stat);
		}
	    }
	  else if (stat (cmp.file[f].name, &cmp.file[f].stat) != 0)
	    cmp.file[f].desc = ERRNO_ENCODE (errno);
	}
    }

  /* Mark files as nonexistent as needed for -N and -P, if they are
     inaccessible empty regular files (the kind of files that 'patch'
     creates to indicate nonexistent backups), or if they are
     top-level files that do not exist but their counterparts do
     exist.  */
  for (f = 0; f < 2; f++)
    if ((new_file || (f == 0 && unidirectional_new_file))
	&& (cmp.file[f].desc == UNOPENED
	    ? (S_ISREG (cmp.file[f].stat.st_mode)
	       && ! (cmp.file[f].stat.st_mode & (S_IRWXU | S_IRWXG | S_IRWXO))
	       && cmp.file[f].stat.st_size == 0)
	    : (cmp.file[f].desc == ERRNO_ENCODE (ENOENT)
	       && ! parent
	       && cmp.file[1 - f].desc == UNOPENED)))
      cmp.file[f].desc = NONEXISTENT;

  for (f = 0; f < 2; f++)
    if (cmp.file[f].desc == NONEXISTENT)
      {
	memset (&cmp.file[f].stat, 0, sizeof cmp.file[f].stat);
	cmp.file[f].stat.st_mode = cmp.file[1 - f].stat.st_mode;
      }

  for (f = 0; f < 2; f++)
    {
      int e = ERRNO_DECODE (cmp.file[f].desc);
      if (0 <= e)
	{
	  errno = e;
	  perror_with_name (cmp.file[f].name);
	  status = EXIT_TROUBLE;
	}
    }

  if (status == EXIT_SUCCESS && ! parent && DIR_P (0) != DIR_P (1))
    {
      /* If one is a directory, and it was specified in the command line,
	 use the file in that dir with the other file's basename.  */

      int fnm_arg = DIR_P (0);
      int dir_arg = 1 - fnm_arg;
      char const *fnm = cmp.file[fnm_arg].name;
      char const *dir = cmp.file[dir_arg].name;
      char const *filename = cmp.file[dir_arg].name = free0
	= dir_file_pathname (dir, base_name (fnm));

      if (strcmp (fnm, "-") == 0)
	fatal ("cannot compare `-' to a directory");

      if (stat (filename, &cmp.file[dir_arg].stat) != 0)
	{
	  perror_with_name (filename);
	  status = EXIT_TROUBLE;
	}
    }

  if (status != EXIT_SUCCESS)
    {
      /* One of the files should exist but does not.  */
    }
  else if (cmp.file[0].desc == NONEXISTENT
	   && cmp.file[1].desc == NONEXISTENT)
    {
      /* Neither file "exists", so there's nothing to compare.  */
    }
  else if ((same_files
	    = (cmp.file[0].desc != NONEXISTENT
	       && cmp.file[1].desc != NONEXISTENT
	       && 0 < same_file (&cmp.file[0].stat, &cmp.file[1].stat)
	       && same_file_attributes (&cmp.file[0].stat,
					&cmp.file[1].stat)))
	   && no_diff_means_no_output)
    {
      /* The two named files are actually the same physical file.
	 We know they are identical without actually reading them.  */
    }
  else if (DIR_P (0) & DIR_P (1))
    {
      if (output_style == OUTPUT_IFDEF)
	fatal ("-D option not supported with directories");

      /* If both are directories, compare the files in them.  */

      if (parent && !recursive)
	{
	  /* But don't compare dir contents one level down
	     unless -r was specified.
	     See POSIX 1003.1-2001 for this format.  */
	  message ("Common subdirectories: %s and %s\n",
		   cmp.file[0].name, cmp.file[1].name);
	}
      else
	status = diff_dirs (&cmp, compare_files);
    }
  else if ((DIR_P (0) | DIR_P (1))
	   || (parent
	       && (! S_ISREG (cmp.file[0].stat.st_mode)
		   || ! S_ISREG (cmp.file[1].stat.st_mode))))
    {
      if (cmp.file[0].desc == NONEXISTENT || cmp.file[1].desc == NONEXISTENT)
	{
	  /* We have a subdirectory that exists only in one directory.  */

	  if ((DIR_P (0) | DIR_P (1))
	      && recursive
	      && (new_file
		  || (unidirectional_new_file
		      && cmp.file[0].desc == NONEXISTENT)))
	    status = diff_dirs (&cmp, compare_files);
	  else
	    {
	      char const *dir
		= parent->file[cmp.file[0].desc == NONEXISTENT].name;

	      /* See POSIX 1003.1-2001 for this format.  */
	      message ("Only in %s: %s\n", dir, name0);

	      status = EXIT_FAILURE;
	    }
	}
      else
	{
	  /* We have two files that are not to be compared.  */

	  /* See POSIX 1003.1-2001 for this format.  */
	  message5 ("File %s is a %s while file %s is a %s\n",
		    file_label[0] ? file_label[0] : cmp.file[0].name,
		    file_type (&cmp.file[0].stat),
		    file_label[1] ? file_label[1] : cmp.file[1].name,
		    file_type (&cmp.file[1].stat));

	  /* This is a difference.  */
	  status = EXIT_FAILURE;
	}
    }
  else if (files_can_be_treated_as_binary
	   && S_ISREG (cmp.file[0].stat.st_mode)
	   && S_ISREG (cmp.file[1].stat.st_mode)
	   && cmp.file[0].stat.st_size != cmp.file[1].stat.st_size)
    {
      message ("Files %s and %s differ\n",
	       file_label[0] ? file_label[0] : cmp.file[0].name,
	       file_label[1] ? file_label[1] : cmp.file[1].name);
      status = EXIT_FAILURE;
    }
  else
    {
      /* Both exist and neither is a directory.  */

      /* Open the files and record their descriptors.  */

      if (cmp.file[0].desc == UNOPENED)
	if ((cmp.file[0].desc = open (cmp.file[0].name, O_RDONLY, 0)) < 0)
	  {
	    perror_with_name (cmp.file[0].name);
	    status = EXIT_TROUBLE;
	  }
      if (cmp.file[1].desc == UNOPENED)
	{
	  if (same_files)
	    cmp.file[1].desc = cmp.file[0].desc;
	  else if ((cmp.file[1].desc = open (cmp.file[1].name, O_RDONLY, 0))
		   < 0)
	    {
	      perror_with_name (cmp.file[1].name);
	      status = EXIT_TROUBLE;
	    }
	}

#if HAVE_SETMODE_DOS
      if (binary)
	for (f = 0; f < 2; f++)
	  if (0 <= cmp.file[f].desc)
	    set_binary_mode (cmp.file[f].desc, true);
#endif

      /* Compare the files, if no error was found.  */

      if (status == EXIT_SUCCESS)
	status = diff_2_files (&cmp);

      /* Close the file descriptors.  */

      if (0 <= cmp.file[0].desc && close (cmp.file[0].desc) != 0)
	{
	  perror_with_name (cmp.file[0].name);
	  status = EXIT_TROUBLE;
	}
      if (0 <= cmp.file[1].desc && cmp.file[0].desc != cmp.file[1].desc
	  && close (cmp.file[1].desc) != 0)
	{
	  perror_with_name (cmp.file[1].name);
	  status = EXIT_TROUBLE;
	}
    }

  /* Now the comparison has been done, if no error prevented it,
     and STATUS is the value this function will return.  */

  if (status == EXIT_SUCCESS)
    {
      if (report_identical_files && !DIR_P (0))
	message ("Files %s and %s are identical\n",
		 file_label[0] ? file_label[0] : cmp.file[0].name,
		 file_label[1] ? file_label[1] : cmp.file[1].name);
    }
  else
    {
      /* Flush stdout so that the user sees differences immediately.
	 This can hurt performance, unfortunately.  */
      if (fflush (stdout) != 0)
	pfatal_with_name (_("standard output"));
    }

  if (free0)
    free (free0);
  if (free1)
    free (free1);

  return status;
}

yeh thanks for your timely help.i will reply after executing the codes

yeh i tried the code but it displays the following error in vc++
fatal error C1083: Cannot open include file: 'diff.h': No such file or directory

I think jephthah might have just been sarcastic with that huge post of his. Even if it worked for you don't turn it in as your assignment because your teacher will immediately recognize it as not your work and flunk you. If he/she doesn't then he's a very stupid teacher.

yeh that is not the matter.but now the code is showing error in including the header files.so please help me in it

you have gave me a full code for diff. but while executing it shows an error in the header files so please help me in it

yeh i need the .h files to make it.please jepthah help me in it very urgent

sigh.

kpnprakash, find the full source for diff, diff3, cmp, and sdiff here:
http://ftp.gnu.org/pub/gnu/diffutils/diffutils-2.8.1.tar.gz

download the archive, unpack it, run the command "./configure", then run the command "make" ... you will find the source code and compiled binaries in the "src" directory.

use the same software for linux or windows, but you may find additional info for windows installation here:
http://gnuwin32.sourceforge.net/packages/diffutils.htm

if you have more questions, the manual is here:
http://www.gnu.org/manual/.

HOWEVER....

i don't think this is going to help you much for your assignment.

good luck

yeh my project is to develop a dll for comparison of two documents in php.
i am developing the code in c to run in vc++ then to develop it as php dll by using zend config.
so i need a simple coding for comparison where i have to bind it in vc++.

thank you for your kindly help jephthah

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