Assignment 6 Programs operate on files

Assignment 6 – (100 points)

Instructions
• Answer the questions individually. Group effort is not allowed.
• For this assignment, you are not allowed to use any library functions other than
printf.
• Ensure that your code runs on remote.cs.binghamton.edu.
• Prototypes must be provided for all functions within the header file define.h.
• Code must be appropriately commented.
• Useful resources:
– Common linux commands: http://www.informit.com/blogs/
blog.aspx?uk=The-10-Most-Important-Linux-Commands
– http://c-faq.com/
– https://cdecl.org/
Questions
1. (100 points) Programs operate on files with specific format. For example, Linux
executes ELF binaries. Microsoft Windows executes PE binaries. ELF is a file
format that tells the loader where and what to find inside the file. Similarly,
a word processor can open .doc files, Zip application can open .zip, .gz, etc.
In order to aid in detecting if a file is of a particular type, a signature is embedded within the file to indicate the type of a file. Often, the signature is the
first few bytes within a file. This will enable an application to quickly identify
if it can operate on the file. In this problem, you will implement a program
file recognizer that accepts a file as command line input, and prints the
1
Table 1: Signature to type mapping. All signatures start from the beginning of the file.
This is only a sample for the assignment. For curious minds, more can be found here:
https://en.wikipedia.org/wiki/List of file signatures
Signature (first few bytes in Hex) File type Expected output
47 49 46 38 39 61 or 47 49 46 38 37 61 GIF Image This is a GIF file.
7f 45 4C 46 ELF file This is an ELF file.
25 50 44 46 PDF file This is a PDF file.
50 4B ZIP file This is a ZIP file.
CA FE BA BE Java class file This is a Java class file.
89 50 4E 47 0D 0A 1A 0A PNG file This is a PNG file.
Anything else Unknown file File type unknown.
format of the file and the program that can open it. NOTE: Although file extensions can sometimes tell what format a file is, it is an unreliable indicator. The
file signature is the true indicator of a file type.
2. You will implement file recognizer.c and file recognizer.h that
contains all your implementation. You will write a Makefile that generates
file recognizer executable. Your program must accept exactly one command line argument (i.e., file name). If more or less than expected number of
arguments are passed, you are to print ”Invalid input.” and exit.
Useful resources
1. Examine fopen(), fscanf() and fclose() functions to perform file IO.
2. Run the find command (e.g., find / -name "*.png") on remote.cs.binghamton.edu
to find files of specific types to test.
Testing your code
In order to test your code, we will run the make command to generate the program. We
will then call the program in a loop on a set of known file types, and in each case, we
will check if the output is as expected in Table 1. We will also provide invalid number
of arguments and non-existent files as arguments. NOTE: The testing process may be
automated. It is your responsibility to ensure that the files are named correctly. You
are advised to test the programs before submitting. Each valid input file is guaranteed
to be at least 10 bytes in size.