Question

wzip and wunzip – MUST BE WRITTEN IN C

The next tools you will build come in a pair, because one (wzip) is a file compression tool, and the other (wunzip) is a file decompression tool.

The type of compression used here is a simple form of compression called run-length encoding(RLE). RLE is quite simple: when you encounter n characters of the same type in a row, the compression tool (wzip) will turn that into the number n and a single instance of the character.

Thus, if we had a file with the following contents:

aaaaaaaaaabbbbthe

tool would turn it (logically) into:

10a4b

However, the exact format of the compressed file is quite important; here, you will write out a 4-byte integer in binary format followed by the single character in ASCII. Thus, a compressed file will consist of some number of 5-byte entries, each of which is comprised of a 4-byte integer (the run length) and the single character.

To write out an integer in binary format (not ASCII), you should use fwrite(). Read the man page for more details. For wzip, all output should be written to standard output (the stdoutfile stream, which, as with stdin, is already open when the program starts running).

Note that typical usage of the wzip tool would thus use shell redirection in order to write the compressed output to a file. For example, to compress the file file.txt into a (hopefully smaller) file.z, you would type:

prompt> ./wzipfile.txt > file.z

The "greater than" sign is a UNIX shell redirection; in this case, it ensures that the output from wzipis written to the file file.z(instead of being printed to the screen). You'll learn more about how this works a little later in the course.

The wunzip tool simply does the reverse of the wzip tool, taking in a compressed file and writing (to standard output again) the uncompressed results. For example, to see the contents of file.txt, you would type:

prompt> ./wunzipfile.z

wunzip should read in the compressed file (likely using fread()) and print out the uncompressed output to standard output using printf().

Details

• Correct invocation should pass one or more files via the command line to the program; if no files are specified, the program should exit with return code 1 and print "wzip: file1 [file2 ...]" (followed by a newline) or "wunzip: file1 [file2 ...]" (followed by a newline) for wzip and wunzip respectively.

• The format of the compressed file must match the description above exactly (a 4-byte integer followed by a character for each run).

• Do note that if multiple files are passed to *wzip, they are compressed into a single compressed output, and when unzipped, will turn into a single uncompressed stream of text (thus, the information that multiple files were originally input into wzip is lost). The same thing holds for wunzip.

Answer 1

Notes :

• To compile the files, use
  • gcc wzip.c -o wzip
  • gcc wunzip.c -o wunzip

Sample Run Sequence :

Step-1

Display content of file "uncompressed_first.txt"

prompt > cat ./uncompressed_first.txt aaaaaaaaaabbbbthe

Step-2

Display content of file "uncompressed_second.txt"

prompt > cat ./uncompressed_second.txt random second file, first line random second file, second line

Step-3

Compress "uncompressed_first.txt", and redirect it to "first.z"

prompt > ./wzip uncompressed_first.txt > first.z 

Step-4

Compress "uncompressed_second.txt", and redirect it to "second.z"

prompt > ./wzip uncompressed_second.txt > second.z

Step-5

Decompress "first.z" only

prompt > ./wunzip first.z aaaaaaaaaabbbbthe 

Step-6

Decompress "second.z" only

prompt > ./wunzip second.z random second file, first line random second file, second line

Step-7

Decompress "first.z" and "second.z" cumulatively

prompt > ./wunzip first.z second.z aaaaaaaaaabbbbthe random second file, first line random second file, second line

Code now follows :

wzip.c

 #include <stdio.h> #include <stdlib.h> void compress(char *path) {   FILE *fp = fopen(path, "rb");   char prev = 0, curr = 0;        int count = 0;  if(fp == NULL)  {               printf("[%s] file does not exist, exiting program ..\n", path);                 exit(1);        }       while(1)        {               curr = fgetc(fp);               if(curr == EOF)                 {                       /*                       * Write when end-of-file reached.                       */                     if(count > 0)                        {                               fwrite(&count, 1, 4, stdout);                               fwrite(&prev, 1, 1, stdout);                        }                       break;          }               if(curr != prev)                {                       /*                       * We got a new character, so first write the count of previous                          * character.                    */                     if(count > 0)                        {                               fwrite(&count, 1, 4, stdout);                               fwrite(&prev, 1, 1, stdout);                        }                       count = 0;              }               count++;                prev = curr;    }       fclose(fp); } int main(int argc, char **argv) {         int i = 0;      if(argc < 2)         {               printf("wzip: file1 [file2 ...]\n");            exit(1);        }       for(i = 1; i < argc; i++)    {               compress(argv[i]);      }               return 0; }

wunzip.c

 #include <stdio.h> #include <stdlib.h> void decompress(char *path) {     char curr = 0;  int count = 0;  FILE *fp = fopen(path, "r");            if(fp == NULL)  {               printf("[%s] file does not exist, exiting program ..\n", path);                 exit(1);        }       while(1)        {               int bytes = fread(&count, 1, 4, fp);                if(bytes != 4)          {                       break;          }               fread(&curr, 1, 1, fp);             {                       int i = 0;                      for(i = 0; i < count; i++)                   {                               fwrite(&curr, 1, 1, stdout);                        }               }       }       fclose(fp); } int main(int argc, char **argv) {         int i = 0;      if(argc < 2)         {               printf("wunzip: file1 [file2 ...]\n");          exit(1);        }       for(i = 1; i < argc; i++)    {               decompress(argv[i]);    }               return 0; }

uncompressed_first.txt

 aaaaaaaaaabbbbthe

uncompressed_second.txt