| CMSC 106 | Project #6 | Fall 2001 |
This project will give you practice processing strings using
pointers and C's character and string processing library functions.
This will allow you to gain a fuller understanding of the
relationship in C between arrays and pointers.
In order to make sure you are using the string functions already defined
for you in <string.h>, you may not use
any loops that process
an array character by character.
You will be writing a program that processes weather data encoded in the
standard international meteorological reporting format. Your program will
read a series of reports, extract the necessary data values, and print an
organized summary of the data for a selected group of locations.
As you read this section, you may also want to refer to the ``Sample
output'' section below.
Your program will first read a list of station names and identifiers.
These will be the locations for which we are interested in obtaining data.
Then it will read a series of encoded data reports. For each report from
a recognized location, it will decode the report to obtain the necessary data
values. After all the data reports have been read and decoded, the program
will print a summary report organized alphabetically by location.
The input data file will consist of 2 sections: the station list and the list of data reports. Each line of the station list will contain a station identifier, the name of the station, and the state in which it is located. The lines will be in the form: CCCC Station Name,SS where
####''. There may or may not be additional information on the last
station identifier line.
There will be no more than 40 stations in the station list.
Following the station list, the program will read the data reports. The reports
will be encoded in the standard format known as METAR.
(The U.S. version of this format is completely described in
Federal Meteorological Handbook Chapter 12
but we will be implementing a subset of the complete code.)
Each report will be on a single line no longer than 120 characters.
A report consists of a series of data groups separated from each other
by a single blank in the format:
CCCC DDhhmmZ dddff[f]Ggg[g]KT nnnVxxx vvvvvSM wwww NNNhhh TT/TD Apppp RMK other
The only data groups which are required to be in a report
are the station identifier and the time of the observation;
all other groups may be omitted. Certain groups may appear more than once in
a particular report.
Data groups other than the station identifier and the time may appear in any order,
but remarks must appear after all other groups.
The various fields are defined as follows:
Duplicate station CCCC
where CCCC is the station identifier.
After the program has read and processed all the station identifiers,
it will read, decode, and store the data reports.
As each report is read, the program must check the station identifier against the
identifiers in the station list. If the identifier does not appear in the list,
the program must print a message and ignore the rest of that data report.
The message must be in the form:
Unknown station CCCC
where CCCC is the identifier in the report.
For each report from a known station, the program must decode each data group and
store the values.
After all of the data reports have been read and decoded, the program must print
out a formatted summary of the data.
The summary must be preceded by a single separator line
containing 10 equal signs ``=''
followed on the next line
by the word ``SUMMARY''.
The summary must be printed in alphabetical order by state abbreviation.
The group of stations for a particular state must be preceded by
a header message, as shown in the sample output.
Within each state, the
stations must be printed in alphabetical order by station name. If there are 2 or more
reports from the same station, the program must print them in the same order
that they were read from the input.
The data reports from each station must be separated by a blank line as shown in
the sample output, and
all data values must be neatly aligned in columns and labeled as shown.
The data values must be listed in the order shown. If a particular data value
was not reported, then the symbol ``NA'' should be printed, except:
If the wind is reported, but the speed is 0, then the word ``Calm'' should be printed. If sky conditions are reported for more than 1 layer, then the conditions for the layer with the maximum cloud coverage should be printed.
arr[i]
and you have a loop that uses i++ - you are traversing the
array character by character. If you are using pointers to a
character array char *ptr and you have a loop that uses
ptr++, you are traversing the array character by character.
strlen, strchr, strcat, strcpy,
strncat, strncpy, strcmp, strncmp,
strcspn, strpbrk, strrchr, strspn,
strstr, or strtok.
All your C programs in this course should be written in ANSI C, which
means they must compile and run correctly with cc -std1 -trapuv
on the OIT
UNIX Class Cluster. You will lose credit if your program generates any
warning messages when it is compiled. Prototypes must appear for all
functions defined, prototypes must be listed at the top of the program file,
and at most one
return statement may be used in any function, including main.
Even if you already know what they are, you may not use any C language
features other than those introduced in Chapters 1 through 13 of your
textbook, plus those in Section 23.4 and any function in Section 23.5 whose
name begins with ``str'', and the language features presented in
lecture while these chapters were covered. In addition neither the
goto nor the continue statement may be used, and the
break statement may not be used in any loop. Your program
may not use the exit() library function at all. Lastly, no
global variables may be used. Using any of these disallowed C features
will result in losing credit.
Your program must make use of C's string library functions anywhere possible. You will lose substantial credit if you write code duplicating their effects, rather than just calling them (e.g., if you write loops to copy or compare strings, search for something in a string, find the length of a string, etc., you will lose credit). The character library functions (textbook section 23.4) may also be used, but you will not be penalized if you duplicate their effects rather than using them. You will lose substantial credit if you use any traversals of an array character by character.
In additon to using the string library functions, your program must be written using user-defined functions where approprriate. Your program must define and call at least six functions you have written; writing more than six such functions would be extremely good practice and the best way to avoid errors in developing your program. If your program doesn't contain, and call, at least six such functions, it will be graded as if it does not work on the primary input- even if its output is correct. Below are ideas for some possible functions; feel free to use others. You are permitted to write as many functions as you want, and if you write any of the functions suggested below they need not perform the exact tasks as described.
Your program must have a comment near the top which contains your name, login ID, student ID, your section number, your TA's name, and an original description of the action and operation of the program. Do not put your alias in this comment! In addition, you must have a comment before each function, explaining its action and operation. Your program should be written using good programming style and formatting, as discussed in class and throughout your textbook. For this project, style is considered to consist of:
You may want to skip this section at first, read the rest of the project,
and come back to study it carefully when you are about to begin writing your
program.
Mistakes with string library functions or pointers are very likely to
result in a fatal program execution error (core dump). A statement may look
completely correct, but just because some string or pointer contains a
certain value the program will fail. This makes it extremely
important to use debug printf statements to narrow down where in your
program the error occurs, before you can even begin to figure out what's
wrong and how to fix it.
Be sure to test each function as it is implemented, before
integrating it with the rest of the program! It is frequently very easy to
test a function which has character array parameters, because you can often
call it by passing any string literals you like into the parameters. As an
example, say you write a function named split, which is supposed to
find the position where a string is to be split in half (perhaps it has
another integer parameter as well). You can call your function several
times, as
split("This is a character string", 15) or
split("Try another character string", 12), and print the result which
your function produces each time. It's easy to see by hand what result your
function should produce, so test it with a number of strings and be certain
it gives the right answer every time. You can write a little test program
file to call your function, or just add these test calls right at the
beginning of main. Once you are positive your function works,
then you can call it as part of your project and be confident that your
program will be likely to work fine.
Here are several common compilation errors having to do with strings produced by the cc compiler on our class machines and what they mean:
(where X is a statement using one of the string library functions)
You probably forgot the #include <string.h> at the top of
your program file.
You are trying to assign something to the name of an array. You
can assign something (a pointer value, or NULL) to a
pointer variable, but not to the name of an array. Maybe you
meant the variable on the left of an assignment to be declared as
a pointer instead of an array.
printf
statements must end with a newline character, or their results may
not show up on the screen if the program has a fatal execution
error (core dump).
printf statement at the beginning of each
function and at the end of each function, before it returns.
These debug print statements can just say something like
``Starting function X'' and ``Leaving function X''. Run your
program again, and if the output shows that some function was
entered but never completed, that function, or one of the
functions it calls, may be where your problem lies. Remember the
terminating \n when inserting debug printf
statements.
'\0').
NULL
before dereferencing them!
Any evidence of unauthorized use of computer accounts or cooperation on
projects will be submitted to the Student Honor Council, which could result
in an XF for the course, suspension, or expulsion from the University.
Projects are to be written INDIVIDUALLY. For academic honesty
purposes, projects are to be considered comparable to a take-home exam. Any
cooperation or exchange of ideas which would be prohibited on an exam is
also prohibited on a project assignment, and WILL BE REPORTED to
the Honor Council.
VIOLATIONS OF ACADEMIC HONESTY INCLUDE:
|
IT IS THE RESPONSIBILITY, UNDER THE UNIVERSITY HONOR POLICY, OF ANY STUDENT WHO LEARNS OF AN INCIDENT OF ACADEMIC DISHONESTY TO REPORT IT TO THEIR INSTRUCTOR.
Your project must be electronically submitted by the date above, before
11:00 pm, to avoid losing credit as described in the syllabus.
No projects more than
two days late will be accepted for credit without prior permission or a
valid medical excuse, as described on your syllabus. Only the project which
you electronically submit, according to the procedures provided, can be
graded; it is your responsibility to test your program and verify
that it works properly before submitting. Lost passwords or other system
problems do not constitute valid justifications for late projects, so
do not put off working on your program or wait to submit it at the last
minute!
Turn in your assignment using the ``submit'' program as before, except
using ``6'' for the project number. You are to submit only the .c file
containing your source code, not the executable version of your program!
If your program is in a file named ``decode.c'', submit would be run as
submit 6 decode.c.
Before you submit your project, you must exactly follow the specific submission checklist in the ``Testing projects before submitting'' handout separately posted by your instructor!
Assuming the name of the executable version of the program is
``decode.x'', here is a sample execution for one input data set.
The
input file is named ``p6.in1'', whose contents are shown as displayed by
the UNIX ``cat''command. Following the data file's contents, the results of
running the program with input redirected from that file are shown. The
p6.in1 file will be available in your class posting account.
Be sure to test your program against a variety of inputs, so you are sure it works in all circumstances!
% cat p6.in1
KDCA Washington National, DC
KBWI Baltimore-Washington International, MD
KADW Andrews Air Force Base, MD
PADK Adak, AK
PANC Anchorage International, AK
PAFA Fairbanks International, AK
KMSP Minneapolis-St. Paul, MN
KDLH Duluth International, MN
KPIH Pocatello, ID
####
KMSP 061453Z 24009KT 6SM HZ FEW250 14/11 A3000 RMK AO2 SLP160 T01390111 53010
KPIH 061456Z 00000KT 10SM -RA BKN070 OVC090 05/04 A3004 RMK AO2 RAE08B50 SLP165 P0000 60000 T00500039 55007
KADW 061255Z 32009KT 7SM FEW040 08/02 A3020 RMK WND DATA ESTMD SLP231 8/100 9/100
KDCA 061351Z 34011KT 10SM CLR 07/02 A3023 RMK AO2 SLP235 T00671022
%
% decode.x < p6.in1
==========
Summary
Conditions for DC:
Location: Washington National
Date/Time: 11/6, 1351
Wind: from 340 degrees at 11 KT
Visibility: 10 miles(s)
Sky conditions: Clear
Temperature: 7 C
Dew Point: 2 C
Pressure: 30.23 in.
Conditions for ID:
Location: Pocatello
Date/Time: 11/6, 1456
Wind: Calm
Visibility: 10 miles(s)
Sky conditions: Overcast at 9000 feet
Weather: Light Rain
Temperature: 5 C
Dew Point: 4 C
Pressure: 30.04 in.
Conditions for MD:
Location: Andrews Air Force Base
Date/Time: 11/6, 1255
Wind: from 320 degrees at 9 KT
Visibility: 7 miles(s)
Sky conditions: Mostly Clear at 4000 feet
Temperature: 8 C
Dew Point: 2 C
Pressure: 30.20 in.
Conditions for MN:
Location: Minneapolis-St. Paul
Date/Time: 11/6, 1453
Wind: from 240 degrees at 9 KT
Visibility: 6 miles(s)
Sky conditions: Mostly Clear at 25000 feet
Weather: Haze
Temperature: 14 C
Dew Point: 11 C
Pressure: 30.00 in.
For this project, the primary input consists of the contents of the
input file given above.
Note that this
primary input does not exercise several conditions discussed above which
your program should work for in order to earn credit for the secondary
inputs.
You may obtain addtional sample data (updated hourly 24 hours a day) at:
United States Weather
(Select a state, then select "Current weather conditions.")