Description
Introduction
Real operating systems are virtually always written in C. We will be using C throughout this course.
This lab lets you revisit some language features specific to C:
Pointers;
Dynamic memory management;
Variadic functions.
Overview
In this lab, you will write an argument manipulator program called nyuc , which stands for Now You
Understand C. Your program will print each command-line argument in its original form, uppercase
form, and lowercase form.
For example, if you run:
It should print:
$ ./nyuc Hello, world
Download
Please download nyuc.tar.xz. You can use the following command to unarchive it:
Your task
The main() function is already given to you in nyuc.c :
[./nyuc] -> [./NYUC] [./nyuc]
[Hello,] -> [HELLO,] [hello,]
[world] -> [WORLD] [world]
$ tar xf nyuc.tar.xz
The main() function invokes two functions, defined in argmanip.h :
Your task is to implement these two functions.
manipulate_args()
#include <ctype.h>
#include <stdio.h>
#include “argmanip.h”
int main(int argc, const char *const *argv) {
char **upper_args = manipulate_args(argc, argv, toupper);
char **lower_args = manipulate_args(argc, argv, tolower);
for (char *const *p = upper_args, *const *q = lower_args; *p && *q; ++argv, ++p, ++q) {
printf(“[%s] -> [%s] [%s]\n”, *argv, *p, *q);
}
free_copied_args(upper_args, lower_args, NULL);
}
#ifndef _ARGMANIP_H_
#define _ARGMANIP_H_
char **manipulate_args(int argc, const char *const *argv, int (*const manip)(int));
void free_copied_args(char **args, …);
#endif
The manipulate_args() function takes three arguments:
argc and argv are the same as the command-line arguments.
manip is a pointer to a function that manipulates a character, such as toupper() and tolower() .
In this function, you will make a “copy” of the argument list. First, you will call malloc() once for the
overall array in which each element is a string of type char * . Then, you will call malloc() for each
element of that array, each of which will hold the manipulated version of each argument. Of course,
you will have to copy each string character-by-character, passing through the manip function as you
go.
free_copied_args()
The free_copied_args() function takes a variable number of arguments, each of which is a “copied”
argument list returned by manipulate_args() . It is terminated by a null argument.
For each argument list, you must free() everything that you have malloc() ed. First, you need to
free() all individual strings. Then, you need to free() the overall array.
Compiling
We will grade your submission on linserv1.cims.nyu.edu, which runs CentOS Linux release 7.9.2009.
We will compile your program using gcc 9.2.0 with the C17 standard and GNU extensions. You need
to run the following command to load it:
We have provided a Makefile , which turns on a few compilation flags to let gcc catch more
potential issues:
To compile your program, type:
Testing
$ module load gcc-9.2
CC=gcc
CFLAGS=-g -pedantic -std=gnu17 -Wall -Werror -Wextra
.PHONY: all
all: nyuc
nyuc: nyuc.o argmanip.o
nyuc.o: nyuc.c argmanip.h
argmanip.o: argmanip.c argmanip.h
.PHONY: clean
clean:
rm -f *.o nyuc
$ make
We will run your program under Valgrind Memcheck, a tool to detect many memory-related errors
that are common in C programs, such as:
Allocating the wrong size of memory.
Using an uninitialized pointer.
Accessing memory after it was freed.
Overrunning a buffer.
Leaking memory.
…
These errors can lead to crashes and unpredictable behavior.
Valgrind is already installed on the Linux server. To run your program under Memcheck, type:
It will print a lot of information. Here is a sample output:
$ valgrind –leak-check=full ./nyuc Hello, world
In addition to printing the correct output, your program must have “0 errors from 0 contexts,” which
means no illegal memory access, no memory leak, etc. Otherwise, Valgrind will give you detailed
information about the memory errors and potential ways to diagnose the issue. You must fix all of
them. You may find gdb useful for debugging.
Submission
You will submit a single file, argmanip.c .
==12345== Memcheck, a memory error detector
==12345== Copyright (C) 2002-2017, and GNU GPL’d, by Julian Seward et al.
==12345== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==12345== Command: ./nyuc Hello, world
==12345==
[./nyuc] -> [./NYUC] [./nyuc]
[Hello,] -> [HELLO,] [hello,]
[world] -> [WORLD] [world]
==12345==
==12345== HEAP SUMMARY:
==12345== in use at exit: 0 bytes in 0 blocks
==12345== total heap usage: 8 allocs, 8 frees, 108 bytes allocated
==12345==
==12345== All heap blocks were freed — no leaks are possible
==12345==
==12345== For lists of detected and suppressed errors, rerun with: -s
==12345== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
You must not modify any provided files ( nyuc.c , argmanip.h , and Makefile ). We will compile your
code together with our provided files and use automated scripts to grade your submission.
Rubric
The total of this lab is 100 points, mapped to 5% of your final grade of this course.
You will get 40 points as long as you submit something meaningful and your program compiles
successfully.
You will get another 30 points if your program prints the correct output.
You will get the final 30 points if your program prints the correct output and Valgrind reports 0
errors. Otherwise, for each error context, there will be a 5-point deduction, up to 30 points.
Tips
If you are experienced in C programming, this lab shouldn’t be too difficult. However, if you are not
familiar with C (even if you know Java), now is an excellent time to catch up before Lab 1 posts. The C
programming language (2nd ed.) by Brian W. Kernighan and Dennis M. Ritchie is a timeless classic
(NYU students can read it online for free), and this C tutorial is a good alternative.
References: Lee et al., Follow the River and You Will Find the C, SIGCSE’11.
