Dec 112017
FC compares two text files and lists the differences between them line by line.
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Category Word Processors
FC compares two text files and lists the differences between them line by line.
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Contents of the FC.DOC file

FC Ver. 2.2
Mike Albert
Copyright (c) 1990


FC compares two text files and lists the differences between them line
by line. FC provides the following benefits:

o FC can show word by word differences between lines that have

o FC helps "C" programmers merge program changes. FC can compare
two "C" programs containing separate sets of changes, and
combine them automatically to make a single program.

o FC lets you do multiple comparisons in one run.

o FC can ignore white space changes. This is useful when you want
to ignore format changes in "C" programs or other text.

o FC never gets confused or "unsynchronized" (as some comparison
programs can).

o FC always finds the smallest set of differences between files,
and never misses matching lines.

o FC lets you list changes in ways that make sense to you by
providing multiple display options. You can also customize FC
to use your favorite options automatically.

If you're familiar with earlier versions of FC, look at section 7 to
learn about the enhancements.

FC can be used on any IBM-compatible computer. Any display adapter that
provides 25 lines of 80 characters will work correctly. FC runs under
MS-DOS versions 2.0 and later, but 3.0 or later is required to customize
the default options. The amount of memory required is dependent on file
size. 100K is enough for small files, while up to 425K is needed for
large ones. Files containing up to 16,300 lines can be compared.


To list the differences between two ASCII text files line by line:
fc file1 file2 options

Changes to file1 to make file2 are listed. Wild-card characters can be
used to do multiple comparisons. The options are:

-a list all lines (whether different or the same)
-s list only lines that are the same
-w ignore white space differences in lines when comparing
-b don't list redundant blank lines
-f list using an alternate format that's useful for editing
-m merge two C programs

-c show context for changes - list up to unchanged
lines as changed when that's clearer - default is 1
-d show differences between changed lines word by word -
= 1 shows minor differences, 10 shows all - default
is 5
-t tab interval is characters - default interval is 8
-u update default options, -u- clears old defaults first
>file3 put difference listing in file file3

A default option can be turned off with a minus sign, e.g. -m- turns off
the -m option. You can also make an option affect only screen output or
file output - an "s" after the option letter indicates screen output,
while "f" indicates file output. E.g. -ds5 specifies that the -d5
option is used for screen output, but doesn't affect output to a file.
This feature is useful when updating default options (with the -u
option), because you often want different options for the two output

The following examples illustrate the use of FC:

Compare two files in the current directory and display the
differences on the screen:

fc prog1.asc prog2.asc

Compare two files in different directories and drives, list all
lines using the alternate listing format (ignoring white space
differences when comparing), and put the difference listing in file

fc d:\backup\prog1.asc c:\tc\prog2.asc -a -f -w >prog2.dif

Compare two files with the same names in different directories and
drives, and display the differences using the alternate listing

fc -f d:\backup\prog1.asc c:\tc

Compare all files with ".c" extensions and the same names in two
different directories:

fc \backup\*.c \tc\*.*

Merge two "C" programs to make a single combined program:

fc dbupdat1.c dbupdat2.c -m >dbupdat3.c

Change the default options for future invocations of FC to -w -c -b
for output to either output device, and -d5 for output to the

fc -u- -w -c -b -ds5

Turn off the -w default option (which was previously set) for output
to a file, but leave it on for screen output:

fc -u -wf-


The arguments to FC (files and options) can be supplied in any order.
The options work as follows:

-a All - FC normally lists only the lines that differ between
the two files. With the -a option, matching lines are also

-s Same - With the -s option, only matching lines are listed.

-w White space - FC normally lists lines as different if any
character in the line (except trailing white space) is
different. With this option, differences in embedded white
space (i.e. space and tab characters) are ignored. This is
useful when you want to ignore differences in the layout of
programs or documents. FC knows about "C" language syntax,
so that only white space that is ignored by a "C" compiler
is ignored by FC.

-b Blanks - FC normally lists all lines that have changed.
With this option, redundant blank lines (i.e. more than one
blank line in a row, or blank lines leading or trailing a
group of changes) aren't shown.

-f Format - This option directs FC to list changes using a
different format that doesn't indent, and shows the line
numbers of changes in both files. This format is useful
when directing the listing to a file used to re-create

-m Merge format - FC merges two "C" programs into a single
program when this option is used. The new file can be
compiled as the first program, the second program, or the
combination of the two. When you #define the symbol
FC_FILE_1, lines present in the first file are included.
FC_FILE_2 does the same thing for the second file. If you
specify both #define's, lines from both programs are
included. This feature is particularly useful when
combining two separate sets of changes to a program. You
merge the two changed programs, examine the combined
program, and remove the #ifdefs to complete the merge. In
most cases the #ifdefs can be removed without incident.
Where there are conflicts between the two sets of changes,
you can resolve them as needed. If you feel brave, you can
compile the merged program with both #define's specified and
see if it works. The merge does not always produce a
compilable program - if the changes involve comments,
#ifdef's, or multiline #defines, the #ifdef's inserted can
conflict with them.

-c Context - When this option is used, FC shows context
surrounding changes to make the listing more readable. This
is done by listing unchanged lines as changed when they are
between changed lines. Use this option when you want to
make the listing easier to understand, and don't care if a
few unchanged lines are listed as changed. The value
indicates how many unchanged lines can be listed as changed.
An of 1 or 2 is usually sufficient. The default value
of is 1.

-d Differences - Show differences between changed lines word by
word. If the listing is shown on the screen, differences
are identified by reverse video. If the listing is directed
to an output file, changes are enclosed in curly brackets
(i.e. "{}"). The value of indicates which differences
are shown - this is useful because showing the differences
between totally different lines is confusing. An of 1
shows only minor differences, while 10 shows all. The
default value of is 5.

-t Tab interval - This option sets the tab interval used to
expand tabs when comparing and listing lines. The default
interval is 8.

-u Update - This feature updates the default options. You can
use this option to make your favorite options the default,
so you don't have to enter them every time you use FC. When
you use the -u option, the current options (i.e. the current
defaults plus options specified on the command line) become
the default. The -u- option is like -u, except that the
current defaults are ignored - only the options shown on the
command line become the new defaults. FC can't update the
options and compare files in the same run, so don't specify
file names when you use the -u or -u- option. This feature
works by changing the program (i.e. fc.exe) file. If you
want, you can make multiple FC's with different default
options by simply copying the fc.exe file with a new name
(e.g. fcmerge.exe) and using the -u option to set the
default values of the copy. This feature only works with
MS-DOS version 3.0 or later.

>file FC normally displays the difference listing on the screen.
or This option directs the listing to the file you specify -
>>file just enter the file name after the ">". If the file already
exists, it is overwritten. The ">>" option can be used in
the same way to append the listing to the end of a file,
instead of overwriting it.

The file names specify a drive and directory in the normal MS-DOS
manner. If no drive is specified, FC looks for files on the current
drive. If no directory is specified, FC looks in the current directory.
The standard MS-DOS wild-card characters may be used to compare multiple
files. When FC finds wild-card characters in the first file name, it
performs a compare for each matching file. A wild-card character in the
second name means use the name (or extension) of the first file. If the
second file is not found FC indicates it is missing, and continues with
other files that match the first name. If you specify a directory or
drive (without a file name and extension) for either the first or second
name, FC acts as though you specified a file and extension of "*.*".
The following examples illustrate these principles:

Compare all files with ".c" extensions and the same names in two
different directories:

fc \backup\*.c \tc

Compare files fcupdate.c1 and fcupdate.c2:

fc fcupdate.c1 *.c2

Compare all files in the current directory with ".c1" extensions
with files that have the same names and ".c2" extensions in the same

fc *.c1 *.c2

Compare all files in current directory with files that have the same
names on the diskette in drive b:

fc . b:

Compare all files with names starting with "a" and having a ".c"
extension with files that have the same names in the directory
"work" that is a subdirectory of the parent directory of the current

fc \backup\a*.c ..\work

The files you compare must contain ASCII text. Displayable characters
with values above hex 7F will also be processed correctly. All
characters except values 00, 07, and 08 (null, backspace, and bell) are
passed through to the difference listing. Character value 09 (tab) is
passed through with the -f and -m formats, but expanded to spaces (as
specified with the -t option) with the normal format. FC expands tabs
as specified in the -t option and removes trailing white space on each
line before comparing. If two lines differ only in this regard, FC will
report that they are the same. Other control characters (e.g. vertical
tabs, page breaks) are not changed before comparing.

Lines can end with carriage return characters (hex value 0D), new line
characters (hex value 0A), or both characters together. FC ignores line
ending characters when comparing, so identical lines with different
ending characters are listed as unchanged. Lines in the difference
listing always end with a carriage return followed by a new line.

FC only processes lines of up to 2,000 characters. If FC encounters a
longer line, it breaks it after the 2,000th character to make two
separate lines.

If you display the difference listing on the screen, you can control the
scrolling. When FC is scrolling, pressing any key makes it pause. When
it pauses, you can use the following keys:

Enter Show another screen full (24 lines)
space Show one more line
s Scroll continuously
ESC Exit the program

You can also use the Ctrl-S and Ctrl-Q keys (the ASCII terminal
convention) to regulate scrolling if you prefer.


Error: argument - is invalid
FC couldn't recognize the argument you specified on the command
line (argument ). Check the list of arguments that FC
accepts to determine what options you can use. You can list the
options FC recognizes by typing "fc ?".

Error: the - option value is wrong
FC couldn't recognize the value specified with the
option on the command line. Most options accept one or two
decimal digits, e.g. -t8 to specify a tab increment of 8. Check
the list of options that FC accepts to determine what values you
can use. You can list the options and values FC recognizes by
typing "fc ?".

Error: more than two file names specified
Error: fewer than two file names specified
FC didn't find the names of two files to compare on the command
line. If you forgot to specify the minus sign ("-") in front of
an option, FC interpreted it as a file name. You must specify
two file names.

Error: both - and - options specified together
FC found two incompatible options ( and ) specified on the
command line. You can only use one at a time.

Error: is too small a value for option - - the lower limit
FC found a value () specified for option that is too
small. You must specify a value greater than or equal to .

Error: is too large a value for option - - the limit is
FC found a value () specified for option that is too
large. You must specify a value less than or equal to .

Error: file wasn't found
FC couldn't find file . If you didn't specify a directory or
drive, FC looked in the current directory and drive. Make sure
you specify the correct file name, with the directory and drive
if needed, on the command line.

Error: no files found at
FC couldn't find any files in directory or drive . Make sure
you specify the correct drive and directory on the command line.

Error: no files match
FC couldn't find any files that matched file name , which
contains wild-card characters. Make sure you specify the
correct file name on the command line.

Error: more than 16,300 lines in file
File contains more than 16,300 lines. FC can only process
files containing up to 16,300 lines. Your only option is to
break your files into smaller files.

Error: not enough memory to process these files
FC needs more memory to process these files than is available.
FC will continue by comparing the remaining files if you
specified multiple comparisons, otherwise it will terminate.
The only way to correct this problem is to run on a machine with
more memory, remove any memory-resident programs, or to split
the file into smaller files. This problem only occurs when
comparing large files on machines with small memory

Warning: Not enough memory to compute word differences in the
following change
FC needs more memory to list the word-by-word differences
between a set of changed lines (as requested with the -d option)
than is available. FC will not list word-by-word differences
for this set of lines, but will with others. This problem only
occurs when comparing large files on machines with small memory

Error: output failed, disk probably full
FC detected an error when writing a file. This only occurs when
the difference listing is directed to a file with the ">" or
">>" options. The most likely cause of this error is a full

Error: file names can't be used with the "-u" option
FC found file names specified on the command line with the -u or
-u- option. You can't update default options and compare files
at the same time.

Error: couldn't update default options
FC couldn't write to the program (i.e. fc.exe) file to update
the default options. This happens when the fc.exe file is on a
write-protected floppy disk, the file has been given the read-
only attribute, you're using an MS-DOS version less than 3.0, or
the file is on a network server and you don't have write
privileges for the file.


FC is distributed as user-supported software. I encourage you to try
the program and share it with friends as long as:

The FC program and this documentation file are not modified and are
distributed together.

FC is not provided as a part of any other product.

No fees, beyond a reasonable fee for media, duplication, or
downloading costs, are charged.

FC is not used for commercial, government, or business purposes
without registration. Each registration is for a single person or a
single computer.

If you find FC useful and decide to use it regularly, you are required
to register. All registration payments will be donated to Oxfam
America, an international development and disaster relief agency. It's
a worthy charity that I've been supporting for many years. For more
information on Oxfam see section 6.

When you register you get the satisfaction of saving lives in Africa,
Asia, and South America, and encourage me to produce more software at
reasonable prices. You also get the following benefits:

I'll notify you of new FC versions when they become available.

I'll send an updated version of FC to you at no additional cost.
You can request this at any time. I'll do this once per registered

I'll answer any questions you have on FC and its use. You can
contact me at the address shown below - I'll respond in writing or
by phone.

If any important bugs are found I will notify you.

I'll make an attempt (but can't guarantee) to fix any problems you

Registration is $25. Please make your check payable to Oxfam America -
I'll send your checks to Oxfam and record your registration information.
I'll also accept original canceled checks or receipts from Oxfam that
list you as the donor. Please send payments, registration information,
and any other correspondence to:

Mike Albert
Suite 42
P. O. Box 2100
Chelmsford, MA 01824

Anyone can order the latest version of FC directly from me for a fee of
$5.00. Just send the order (make sure it contains your mailing address)
with your check to the above address. You'll receive a 5 1/4 inch 360Kb
floppy disk containing the executable and documentation files. If you
need other formats (5 1/4 inch 1.2Mb or 3 1/2 inch 1.44Mb) I can provide
them. I'll also include other shareware products I produce. If you
live outside North America, please send extra money for the increased

I welcome all comments and suggestions concerning FC. I'd like to know
how you are using FC, where you obtained it, and what problems, bugs, or
weaknesses you find. If you tell me about enhancements or changes
you're interested in, I'll make an effort to provide them.

This program is provided "as is" without warranty of any kind, either
express or implied, but not limited to the implied warranties of
merchantability or fitness for a particular purpose. The entire risk as
to the results and performance of the program is assumed by the user.
Should the program prove defective, the user assumes the entire cost of
all necessary servicing, repair, or correction.


As stated in Oxfam literature,

"Oxfam America is an international agency that funds self-help
development projects and disaster relief in poor countries in
Africa, Asia, and Latin America, and also prepares and distributes
educational materials for people in the United States on the issues
of development and hunger. The name "Oxfam" comes from the Oxford
Committee for Famine Relief, founded in England in 1942. Oxfam
America, based in Boston, was formed in 1970, and is one of seven
autonomous Oxfams around the world (Great Britain, Australia,
Belgium, Canada, Quebec, Hong Kong and the United States). Oxfam is
a nonsectarian, nonprofit agency that neither seeks or accepts U.S.

government funds. All contributions are tax-deductible to the
extent permitted by law."

For more information, you can phone Oxfam at 617-482-1211, or write to
them at:

Oxfam America
115 Broadway
Boston, MA 02116


FC version 2.2 - 6/5/90

Increased the speed - some comparisons take only 60% as long as
previous versions.

Fixed a problem displaying per word changes in very long lines
(around 2000 characters).

Fixed a problem that occurred when '.' was used to indicate a

Fixed error in handling Ctrl-C when display scrolling is paused.

FC version 2.1 - 4/29/90

Altered the difference computation for word changes within lines
to pick more intuitive changes. In some cases there's more than
one set of minimal changes. Version 2.0 could pick differences
that were minimal, but difficult to understand.

Increased the speed.

Fixed a problem in which characters with values above 127 were
sometimes treated as spaces when comparing.

Fixed a minor formatting problem with the difference listing
produced with the -m option.

Fixed a minor problem that occurred when another program invoked
FC and input redirection was used.

FC version 2.0 - 3/21/90

Added -d option to show word-by-word differences between changed

Added -m option to merge two "C" source programs.

Added comparison of multiple files in a single run - this is
invoked by specifying wild-card characters in file names.

Added -w option to ignore white space differences when

Added -b option to not show redundant blank lines in difference

Added -c option to show changes in context.

Added -u option to let the user set default options.

Added -f option to produce a new format for the difference

Increased the speed - some comparisons take only half the time
of the previous version.

Added separate sets of options that are selected based on the
output device, i.e. the screen or a redirected output file.

Altered the difference computation to pick more intuitive
changes. In some cases there's more than one set of minimal
changes. Previous FC versions could pick differences that were
minimal, but difficult to understand.

Added support of Ctrl-S and Ctrl-Q to suspend and resume display

Added support of files that use carriage return characters
(instead of new line characters) to end lines.

FC version 1.3 - 7/10/89

Corrected problem in which matching lines occasionally were
listed as different.

Added -s option to list only lines that match.

FC version 1.2 - 3/20/89

Increased speed.

Increased number of lines that can be compared - from 8,000 to

Increased maximum line length from 1000 to 2000 characters.

Added display of characters with values above 7F. This is
particularly useful for non-English text.

Fixed bug that occurred when processing a very large (around
8,000 line) file - FC would incorrectly report that there was
insufficient memory to process the file.

Removed testing for Ctrl-Z (MSDOS end of file marker) in the
middle of a file - Ctrl-Z is now compared and displayed just
like other characters.

FC version 1.1 - 2/16/89

Added documentation (that you're reading now).

Added interactive control of screen display.

Changed informational and usage messages displayed by program.

Corrected problem that occurred when long lines were displayed.

Added accept of Ctrl-C during file read.

FC version 1.0 - 1/9/89

Initial release of FC program.

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