Problem $1$

We are going to develop our own tar and untar tools to copy$/$extract files into$/$from an

archive.

The first thing is to figure out the format of the archive. In addition to storing the file content,

the archive file must also store the original filename so that it can be recreated on extraction.

The following is a suggested archive file format:

mytar

$[$filename$-1]$

$[$filesize$-1]$

$[$filedata$-1][$filename$-2]$

$[$filesize$-2]$

$[$filedata$-2]...$

A couple comments on the archive format:

$$ The file begins with the magic word $$mytar

$$ for identification purposes. This is a

common technique for application to identify if the file is of the right type $($instead of

relying on file extension$)$ and if not, abort the operation.

$$ Files are stored in the archive one after the other, prefixed by the filename and the

file size. The file size is essential for determining where the file$$s data ends and the

next file begins.

$$ There is no end$-$of$-$archive marker $$ it$$s just the end of the file.

$$ Filename and file size are stored as ASCII text, followed by a newline char $$

$.$

$$ Both text and binary files can be archived.

a$)$ Develop mytar.c which will copy source files specified in the command$-$line

arguments into the archive file specified.

$$ You are highly recommended to test your program in a separate directory so

that any bugs will not destroy your C source files!

$$ To facilitate debugging, try archiving short text files first $($e$.$g$.,$ C source files$).$

The resultant archive file can then be inspected in gedit directly.

Example: $($No argument given, show usage.$)$

$ $./$mytar

Usage: $./$mytar outputfile infile$1[$infile$2]...$

Example: $($Archive files. Note the wildcard $*.$c will expand $($by the shell$)$ into a list of matching

filenames and be passed to main$()$s argc$/$argv$[]$ parameters.$)$

$ $./$mytar myfiles.mt $*.$c

Creating archive file $...$

Adding file mytar.c to archive $...$

Adding file myuntar.c to archive $...$

Total $2$ files and $8887$ bytes archived successfully.

Example: $($Archive files. Overwrite handling.$)$

$ $./$mytar myfiles.mt $*.$c

Output file myfiles.mt already exists, overwrite? $($y$/$N$)$: n

Aborted!

b$)$ Develop myuntar.c which will extract files from an archive file to an optional output

path.

$$ You are highly recommended to test your program in a separate directory so that any

bugs will not destroy your C source files!

$$ The output path, if not specified, is the current working path. Otherwise, the output

path will be prepended to the original filenames. See below for examples.

$$ If the output file already exists then it will be truncated and overwritten.

Example: $($No argument given, show usage.$)$

$ $./$myuntar

Usage: $./$myuntar inputfile $[$output$\_$path$]$

Example: $($Extract files to an output path $$out$.$ Note the output path must exist or it will

abort.$)$

$ $./$myuntar myfiles.mt nodir

Reading archive file $...$

Failed to open destination file nodir$/$mytar$.$c$,$ reason: No such file or

directory

$ mkdir outdir

$ $./$myuntar myfiles.mt outdir

Reading archive file $...$

Extracting file outdir$/$mytar$.$c $...$

Extracting file outdir$/$myuntar$.$c $...$

Total $2$ files and $8887$ bytes extracted successfully.

c$)$ Does your mytar.c work correctly if one of the input files is a directory? Try the

following and see what happens. Add the logic to detect directories and skip them.

Put your solution into mytar$2.$c$.$

Page $2/5$

Example: $($Extract files to an output path $$out$.$ Note the output path must exist or it will

abort.$)$

$ $./$mytar myfiles.mt $*$

Creating archive file $...$

Adding file mytar to archive $...$

Adding file mytar.c to archive $...$

Adding file myuntar to archive $...$

Adding file myuntar.c to archive $...$

Input file outdir is a directory, skipped..

Total $4$ files and $35407$ bytes archived successfully.

d$)$ Another annoyance is when you already have the archive file and you want to

overwrite it$.$ But if your input wildcard is $*$ then the archive file will be included as

well which is not correct behavior. Add the logic to detect this and put your solution

into mytar$3.$c $($copied from mytar$2.$c$).$

Example: $($Automatically skip the archive file from the list of source files.$)$

$ $./$mytar myfiles.mt $*$

Output file myfiles.mt already exists, overwrite? $($y$/$N$)$: y

Creating archive file $...$

Input file same as output file, skipped.

Adding file mytar to archive $...$

Adding file mytar.c to archive $...$

Adding file myuntar to archive $...$

Adding file myuntar.c to archive $...$

Input file outdir is a directory, skipped..

Total $4$ files and $35407$ bytes archived successfully.