Description
1. Overview
This lab introduces you to malloc(3), free(3), and strdup(3), linked lists in C, dangling pointers, and memory leak. There are two programs in this assignment, each
of which will read in data, insert the data into a linked list in sorted order, and print
out the data. One program will use double and the other will use character strings
represented as char*. See the code/ subdirectory. Also, read the man page : man -s
3 malloc.
2. Program nsort specification
As usual, the program is presented in the form of a Unix man page specification.
NAME
nsort − sort numbers read from stdin
SYNOPSIS
nsort [−d]
DESCRIPTION
Reads in numbers from stdin, and stops at end of file. Error messages are
printed for any word that is not recognized by scanf(3) as a number. The numbers are printed sorted in ascending order, one per line, to stdout using the
printf(3) format “%24.15g\n”.
OPTIONS
Options are scanned by getopt(3).
−d Output is printed in debug format with pointers in “[%p]” format.
EXIT STATUS
0 No errors were detected.
1 Syntactically incorrect input numbers were detected.
3. Program lsort specification
As usual, the program is presented in the form of a Unix man page specification.
NAME
lsort − sort lines read from stdin
SYNOPSIS
lsort [−d]
DESCRIPTION
Reads in lines from stdin, stopping at end of file. The lines are printed sorted
in ascending order to stdout. The output should be the same as that from
sort(1).
CMPS-012M • Spring 2013 • Lab 6 • malloc(3) and free(3) page 2 of 3
OPTIONS
Options are scanned by getopt(3).
−d Output is printed in debug format with pointers in “[%p]” format.
EXIT STATUS
0 No errors were detected.
1 An unterminated line or a line longer than 80 characters was detected.
4. Preparation
Before you begin, study the code provided.
(1) The file code/Makefile is complete, but no source code has been provided for
the two C programs.
(2) Read the man(1) pages for malloc(3), free(3), and strdup(3).
(3) Study the code in the misc subdirectory. None of the code in this directory
should be directly copied into your programs, but parts of it will be adapted for
use.
(4) Study the sample code sortlist.java, which shows you the exact algorithm
you are to use for your program. It is exactly equivalent to lsort when you
run without options. It is similar to nsort. Adapt its algorithm line by line.
5. Program nsort implementation
This program deals only with lists of numbers.
(1) Study the file scanf.c to see how to use scanf(3) to read numbers from stdin.
(2) Study the file numlist.c to see how to declare a linked list of nodes containing
numbers and how to use malloc(3) to allocate space and how to use free(3) to
free up the nodes when done. C does not have a garbage collector.
(3) Print out the numbers either in ordinary format or in debug format.
(4) Instead of inserting the new node onto the front of the list, put in the list in
the proper position. See the program sortlist.java for the insertion algorithm.
(5) Use the command valgrind –leak-check=full to check for memory leak.
6. Program lsort implementation
This program deals with lists of strings, so that each node uses two heap objects.
(1) To begin work, cp nsort.c lsort.c. Change the declaration of the item field
from double to char *.
(2) Look at strlist.c to see how strings are handled. Create a character buffer of
dimension 82 (char buffer[82];) and read in lines. Insert each line into the
list. Print an error message for any line that is not terminated by a newline
character (’\n’). The buffer holds up to 80 characters read in from each line,
plus the newline character plus the null plug (’\0’).
CMPS-012M • Spring 2013 • Lab 6 • malloc(3) and free(3) page 3 of 3
(3) When comparing strings in the insertion routine, use strcmp(3). This works
very much like compareTo in Java.
(4) Use the command valgrind –leak-check=full to check for memory leak.
7. What to submit
Submit the files nsort.c, lsort.c, and Makefile. Your Makefile should build the executables nsort and lsort from the target all. If you are doing pair programming,
see /afs/cats.ucsc.edu/courses/cmps012b-wm/Syllabus/pair-programming/ and follow those instructions as well.
