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Shun Kashiwa edited this page Apr 8, 2023 · 5 revisions

Project 1: Bobcat


Photo by Bucker1999

GOAL: This project serves as a refresher for building software in the C programming language. In particular, the project will involve a review of Linux system calls, buffering file I/O, memory management, etc.

IMPORTANT: Please read SETUP on setting up the development environment.

Project Details

In this project, you will implement a command-line tool, bobcat. bobcat should work just like cat, except it does not support any of the options.

The command is invoked with zero or more file operands: ./bobcat [file ...]. The bobcat reads files sequentially, writing them to the standard output. The file operands are processed in command-line order. If file is a single dash (-) or absent, bobcat reads from the standard input.

The bobcat utility exits 0 on success, and >0 if an error occurs.

Examples

Here, we illustrate how your command should operate with examples.

Suppose that you are in a directory that has three files: file1, file2, and file3.

bobcat file1

will print the contents of file1 to the standard output.

bobcat file1 - file2 - file3

will print the contents of file1, print data it receives from the standard input until it receives an EOF (^D) character, print the contents of file2, read and output contents of the standard input again, then finally output the contents of file3.

bobcat

will open the standard input, as file is absent, just like bobcat -.

bobcat file1 hello file2

will print the contents of file1. Because hello does not exist, it will print the error: bobcat: hello: No such file or directory to the standard error. The command should process the rest of the operands, and will print the contents of the file2. Because there was an error during the execution, the exit status of the command will be >0.

As stated, bobcat should work the same way as cat. When in doubt, check the behavior of cat.

Notes

In addition to the functionality described above, bobcat should meet the following functionality and limitations:

  • bobcat must be reasonably time efficient: it should buffer file input and output
  • bobcat must be reasonably space efficient: it should use at most 1MB of memory regardless of input.
  • bobcat must not leak any memory (i.e., it should free all memory that it allocates).
  • bobcat should not crash
  • bobcat must use the read and write system calls for reading a file and writing to the standard output.
    • In particular, it cannot use the following functions from the stdio.h library: fwrite, fread, variants of put and get.
  • bobcat cannot use functions, like system(3), that execute external programs.
  • all source files must be formatted using clang-format. run make format to format bobcat.c.
  • You may modify Makefile to add scripts, but when you submit, make sure that make produces the bobcat executable using clang with -Wall -Wextra -Werror -std=c11 -pedantic flags.

Hints

  • Use read(2) to read a file and write(2) to write to the standard output.
  • Use warn(3) to produce warnings. Pass the file name to match the output of cat.
  • To check the return code of your program, run your program until completion and then type echo $? in your terminal.
  • Use valgrind --leak-check=full to check your program for memory leaks
  • Make sure your code works on the environment described in SETUP
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