ProfitPress Mega CDROM2 Shareware Freeware (MSDOS)(1992)(Eng)

home *** CD-ROM | disk | FTP | other *** search

/ ProfitPress Mega CDROM2 …eeware (MSDOS)(1992)(Eng) / ProfitPress-MegaCDROM2.B6I / MAGAZINE / MISC / CNEWS017.ZIP / CNEWS017.DOC next >

Wrap

Text File | 1989-09-25 | 30.7 KB | 963 lines

Issue 17 C News 1 *--------------------------------------------------------------* | C NEWS - International C Electronic Newsletter/Journal | | "Dedicated to the Art of C Programming" | | | | Founded 12/27/87 | *--------------------------------------------------------------* Table of Contents THE HEAP: Messages from the Editor ...................... 2 COMMAND LINE ARGUMENTS IN C by Jim Singleton .............. 4 BOOK REVIEW by Jim Singleton ........................... 6 BEGINNERS CORNER: By Wayne Dernoncourt ................. 8 PEPTO: A SHAREWARE SOURCE CODE COMPRESSOR by Jim Singleton. 13 ARTICLE SUBMISSION STANDARDS ......................... 15 HOW TO GET HOLD OF US HERE AT CNEWS........................ 16 "C News" is an Electronic Journal published by the C BBS in Burke, VA on a monthly basis. The subject for C News is the C programming language, as well as any derivatives like C++. All readers are encouraged to submit articles, reviews, or comments for submission. C News is freely distributed, but can not be sold for a profit, or cannot have a charge assessed to cover distribution costs. All articles, and reviews become the property of C News and cannot be included in other publications without written permission from the C News Editorial Staff. To do so is in direct violation of the C News License agreement. Copies of which are available from the C BBS. This publication is Copyrighted under U.S. Copyright Law. Issue 17 C News 2 ================================================================= THE HEAP: Messages from the Editor ================================================================= Welcome to another issue of C News. Jim, Dan, and Wayne have worked hard to put this issue together, and deserve a round of applause for their fine efforts. A couple of weeks ago, I placed a message in the Fidonet C Echo asking for ideas on articles for C News. The response was excellent. The C News staff and I will be reviewing the ideas that have been submitted and determine which subjects we can cover and in what issue they will appear. As always, you are encouraged to submit ideas to the C BBS, via postal mail or MCI mail. One area that we will begin a series on in the next issue is sort and search algorithms, to include: Quicksort, Bubblesort, B-Trees, and Linked Lists. Each algorithm will be presented in theory, pseudocode and a 'c' code example. Also, if time permits in the next few months, I will begin a beginners column in MS Windows programming. I would also like to cover OS/2 programming as the two are closely related. However the cost of the OS/2 development kit prohibits me from exploring the latter. Maybe in time, Microsoft may decide to lower the cost to something reasonable. Sometime later in the week, I will be sending all of the C News issues to date to the "C Users Group" for inclusion in their library. I'll let you know whether CUG accepts the disks or not in the next issue of C News. C News also has a new "European" C News BBS and Editor. The newcomer to the C News staff is Rob Koel, a young computer professional in Holland. Rob runs a BBS in holland that has it's own C News section which contains all of the issues of C News, and a message section where you can leave messages to us. Rob will pack of the message sand forward them to us here in the US. As soon as Rob, let's me know his BBS number I will post it here in this column. Finally, Jim Singleton represented C News at the East Coast SOG in York, PA this month. Jim presented C News and discussed the future of the newsletter and solicited thoughts and ideas on C News. Jim and I have not had a chance to talk since the SOG, I will fill you in on the details in the next issue. Thanks for the continued support, and we look forward to a continued relationship with our readers and friends around the Issue 17 C News 3 globe. Keep those postcards coming!!! Barry Lynch Editor - C News Issue 17 C News 4 ================================================================= COMMAND LINE ARGUMENTS IN C by Jim Singleton ================================================================= I was looking through a C text the other day (see the review of "The Spirit of C: An Introduction to Modern Programming" elsewhere in this issue) and I noticed that the very last topic which was covered was passing command-line parameters. I admit that passing command-line parameters is probably not one of the first topics which a C programmer should learn. After all, how many parameters do you need to pass to print "Hello world"? At the same time, I can see an argument for covering the topic a bit earlier, perhaps when discussing functions. It's really just a special case of passing a parameter to a function -- which happens to be main(). Anyway, if you've ever wondered how to pass a parameter on the command-line, just read on. In order to pass a parameter to the program, main() must be defined as having two arguments, as shown: void main(int argc, char *argv[]) { . . . } Where argc is an integer value representing the number of arguments typed on the command-line. The second argument, argv[], is an array of character pointers. While these arguments may also be declared as: void main(argc, argv) int argc; char **argv; { } these arguments must be declared as the type shown. The first value of this array of character pointers, argv[0], is always the name of the program. For example, let's assume we have a program called READ and it's executed, in DOS, as: C> read [filename] We would enter: C> read CNEWS017.NWS Issue 17 C News 5 In this example, argc has a value of 2 (for the program and the filename), argv[0] is "read" and argv[1] is "CNEWS017.NWS". If we were to enter: C> read CNEWS017.NWS ASCII we would find: argc = 3 argv[0] == "read" argv[1] == "CNEWS017.NWS" argv[2] == "ASCII" You may have noticed that the arguments passed are always stored as character strings. If we have: C> read CNEWS017.NWS 2 We find that argv[2] is a pointer to the character string "2". In order to use this value as a number, the program must convert the string. This is easily accomplished by using functions such as atof(), atoi(), etc. The program DICE.C is an example of a program which requires passing a parameter upon execution. (Two versions of DICE.C, one for Turbo C and one for Microsoft C/Quick C, are contained in the accompanying file DICE.LZH.) As the program simulates the rolling of a user-specified number of dice, the number of the dice is entered at the time of execution. In this example, the number of dice, which is stored as a character string, must be converted to an integer, which is done using atoi(). DICE.C also shows how the value of argc can be used to determine that the correct number of parameters has been entered. While we have seen that passing parameters to a program upon execution isn't hard, don't get carried away with command- line arguments. We wouldn't want something like: C> read CNEWS017.NWS -ascii -double-spaced -odd-pages -titled -two-per-screen would we? (Okay, okay, if we were using Berkeley Unix we would, but otherwise, we would not.) Besides, the more parameters that can be passed, the more complicated the program is for the user. Issue 17 C News 6 ================================================================= BOOK REVIEW by Jim Singleton ================================================================= Title: The Spirit of C An Introduction to Modern Programming (Student Copy) Author/s: Henry Mullish and Herbert L. Cooper Publisher: West Publishing Company 50 West Kellog Boulevard P. O. Box 64526 Saint Paul, MN 55164-1003 ISBN #: 0-314-28500-8 Unlike most of the books which have been reviewed in the C NEWS, "The Spirit of C An Introduction to Modern Programming" is somewhat different because it is a textbook. (The only other books reviewed in the C NEWS which I would consider textbooks might be Thomas Plum's "Learning to Program in C" and "Reliable Data Structures in C".) Before you say, "Oh, it's a textbook, it must be boring" and stop reading this review, hold on a minute. Of all the textbooks I own, from all the classes I've taken, this is the only one which is usually within reach. I say "usually" because I normally keep it at work, as one of my two C references. (There are other C books, a number of them, sitting above my computer at home.) One thing, which I have to point out, that separates "The Spirit of C" from all other C books I have read or looked through is the first example program. Rather than the normal "Hello world" program, the first program is an interactive program to calculate the hypotenuse of a right triangle. Had this been the first C program I had ever seen, I'd have probably gone back to whatever language I was using before C! Luckily, the first program for the reader is asked to enter is much simpler. "The Spirit of C" is a very readable text. It's not a book I might take to the beach (then again, I have taken programming books on vacation, so...); but it is a lot less dry than most textbooks, especially the textbook I learned FORTRAN from. The sixteen chapters are well organized and filled with example programs. Virtually every example program has an example of its output immediately following the program. Each chapter is divided into four parts. The first part goes into the topics which are covered in that particular chapter. The second part is titled, "The Spirit of C" and is used to illustrate the material covered in the chapter by Issue 17 C News 7 demonstrating the solution of a real life programming problem. Also included in this section are discussions of programming style, debugging (starting with chapter 5), and other related topics. The third section of each chapter is a series of questions concerning the information presented in the chapter, followed by the answers. The fourth and final section of each chapter is a number of programming exercises. Unfortunately, the solutions to these programming problems are not in the text, but are included in the instructors edition. At the end of the book, where the answers to the programming problems should be, are six appendices: a C reference guide, common library functions, ASCII character codes, a discussion of UNIX, a listing of keywords, and a guide to the programming debugging hints presented elsewhere in the book. The appendices are followed by a good index. Easy to read and loaded with examples, "The Spirit of C" sounds like the ideal book to learn C from. While I am sure you could learn to program from this book, without an instructor (look at the people who have learned C from K&R), I wouldn't recommend it as a first book. Why? That's hard to say. It wasn't the first book on C I had read, but when I spoke to some students who were using it in a class, who had not been exposed to C, almost all had reservations about it and had gotten some other introductory C book. Another strike against it is that it is rather hard to find, especially outside of a college bookstore. Issue 17 C News 8 ================================================================= BEGINNERS CORNER: By Wayne Dernoncourt ================================================================= In the last article we discussed the concept of passing back multiple pieces of data from a function. As part of this discussion the concept of an address was introduced, along with reading and writing data at this address. This was all discussed along with scope - that is, how long data is good for. This month we're going to step back and look at how functions that are supplied with the operating system pass data back and forth (this will be done primarily through the use of file system calls). Next month we're going to continue to look at how file I/O is performed. The month after that we're going to discuss writing and using your own data structures. One of the most elementary things that a program does is create a file. That's one item that we haven't done yet. This will be remedied in this article. To start off with, the operating system (most operating systems, anyway) needs some information before it can work with files. For example, the operating system has to know the name and location (i.e. the pathname) of the file, and it has to know how you're going to call it (i.e. which one of several files or printers that you're currently using - which one do you want to use). Also you should tell it whether you're going to read the file or write the file and whether you want to treat the file as a text file or as a binary file. All of this information is usually specified in the 'open' statement. For our first example we are going to come up with a program to fill the following need. A user has a file of a scanned (digitized) drawing stored in the computer in a known format (i.e. AutoCad). However, the scanner software didn't block the file into the needed 80 character records, it left it as one record that was 350,000 characters long. The requirement is to read in the original file and insert a new line character after every 80 characters. In our first example, instead of an 'open' statement, we're going to use an 'fopen' statement. It performs the same function, but is specifically intended for buffered file I/O. The following pseudo-code is designed to fill this need. As the name implies, pseudo-code isn't real program code. There is more English, but it doesn't have all of the control structures that will be needed. But it serves as a stepping stone between the problem statement and definition and the program source code. Issue 17 C News 9 /* This program is to demonstrate how to use files */ /* Open an input file <-on error quit-> open an output file <-on error quit-> initialize a counter to zero that will track the number of characters going into the output for each record until you hit the end of file (EOF), do the following: read a character write a character increment counter if counter is greater than 79 then write a new line reset counter to zero end-if end-until This is the C source code that has been written from the pseudo-code above. Notice that there are some changes between the two, but that on the whole the program follows the pseudo-code. #include <stdio.h> main() { int char_cnt = 0; /* This is our increment counter */ char in_char; /* This is the character variable */ FILE *in, *out; /* Set up pointers to file data structures */ if ((in = fopen("notes.log", "rt")) == NULL) { fprintf (stderr, "Oops, where is input file at?\n"); return(1); } if ((out = fopen("notes.new", "wt")) == NULL) { fprintf (stderr, "Oops, how about the output file"); return(1); } while (!feof(in)) { in_char = fgetc(in); fputc (in_char, out); char_cnt++; if (char_cnt > 79) { fputc('\n', out); char_cnt = 0; } } Issue 17 C News 10 fclose(in); fclose(out); } The 'fopen' call takes the information from the function arguments and creates a data structure of type FILE. Some of this information is supplied by the operating system when the 'fopen' call is used. Examples of the information stored in the data structure include the file status (read only, write only, read write, etc.), the error status, a file descriptor, buffer size (the buffer size on a floppy is usually smaller than that of a hard disk), the address of the data transfer buffer and a currently active pointer. The values returned by the 'fopen' calls are pointers to the memory locations where the data structures reside. These are assigned to the variables 'in' and 'out'. These variables are then checked for equality to 'NULL'. NULL is a macro defined in the stdio.h header file that is the value returned by 'fopen' when an error has occurred. In many C implementations this macro is a synonym for 0, but portable code should not rely on this as it is not always true. Anyway, if the 'in' and 'out' pointer variables aren't NULL, this implies that the files could be opened. More specifically, the first file existed and could be opened and that the second file could be created. The double equal sign in the 'if' statement is how the C language denotes the equality condition check, i.e. make sure that the variable 'in' is equal to 'NULL'. If either variable is equal to NULL, print out an error message and stop the program. You may have noticed that three operations actually take place in these first two 'if' statements: 1. A file is opened for either reading or writing 2. An assignment to a pointer variable is made 3. The pointer variable is checked for validity The next thing that may strike you as a bit odd is the expression: while (!feof(in)) What this expression means is that while the expression in the parentheses is true, do whatever follows the expression. In this particular case, feof(in) is a macro to determine whether or not the end of the file has been reached, the value of the expression is true if the end of the file has been reached, otherwise it's false. The leading exclamation mark negates the expression that follows. So what this whole line means in english is "do the following until I hit the end of the input file". Issue 17 C News 11 The 'fgetc' function gets a character from the input file (this is singular, not plural) and assigns it to the variable 'in_char'. The same character is then written to the output file and the number of characters written to that output record is then incremented by one. Let's talk about this last operation in a little bit more detail. Back in the second issue of this column, I talked about the following operations: 1. += 2. -= 3. /= 4. *= It turns out there are another class of operators called the increment/decrement operators. These operate just as you might imagine, they either increment or decrement the variable being operated on. The only variables that this makes any sense on are integers and maybe characters. In the case of the increment operators, the variable is incremented by one, or: i = i + 1; is the same as i++; The only difference between the increment and decrement operators is that instead of adding one to the variable, one is subtracted from the variable. These operators can be extremely useful. For example, consider the following code fragment: int i,j,k; i = 1; j = i++; k = --i; printf ("%d %d %d\n", i, j, k); What would be printed on the screen? The number '1' three times. In this case, the pre-increment and post-decrement operators have two stages, the assignment phase and then either the increment or decrement phase. Initially the variable 'i' is assigned the value of 1. The variable 'j' is then assigned whatever value is held by the variable 'i', then the variable 'i' is incremented (notice the plus signs after the variable, this is called a post-increment operator). Then the variable 'i' is decremented back to 1 by the next line (notice the minus signs before the variable, this is called a pre-decrement operator), then the variable 'k' is assigned the value of the variable 'i'. There are also pre-increment (++i) and Issue 17 C News 12 post-decrement operators (i--). Obviously, you can use any legitimate variable that you want. Now that we've discussed the increment/decrement operators briefly, let's get back to the discussion of this month's program. After the counter is incremented, check to see if it is greater than 79, if it is, put a new line out to the file and reset the counter to zero, then go back to reading the input file. The files are usually automatically closed upon exit, but to be neat, we will close them manually with the 'fclose' function. This closes out this edition of my column. The whole point of this column is to demonstrate that a lot of data (in this case the data required for file use) can be passed among functions with the programmer just having to make allowances for it's use, and not be real concerned with how it works. In next months column, we'll discuss file I/O some more and pointers. Issue 17 C News 13 ================================================================= PEPTO: A SHAREWARE SOURCE CODE COMPRESSOR by Jim Singleton ================================================================= Recently, I was listing the new files on the C BBS and noticed the following: PEPTO1.ARC 14208 08-07-89 Odd Utility of the month! Compress C Src code for Compiling I decided to see exactly what this program did that qualified it as the "Odd Utility of the month!" (Not to mention that the name of the program was enough to grab my attention.) I guess I've always had a thing for odd and interesting little utilities and programs. So, I went ahead and downloaded PEPTO1.ARC. Upon unarchiving PEPTO1.ARC, I found myself with three files: PEPTO.C, PEPTO.EXE, and PEPTO.TXT, the source, executable, and text files for PEPTO. What does PEPTO do? Well, PEPTO is designed to shrink source code and header files for C programs. Why? To reduce space requirements and decrease compile times by compressing the system header files. The author also states that PEPTO can be used for distribution of secure copies of source code by changing major variable names and compressing the source. PEPTO is easy to use. The commands can be entered on the command line individually: PEPTO DICE.C, using wildcards: PEPTO *.H There is also a feature, /C, which prevents the lines in the source file from being concatenated: PEPTO /C HELLO.C This last feature can be useful if the C compiler you use does not like long command lines. After a file has been compressed, the compressed version has the extension *.PEP. Issue 17 C News 14 What does a program that has been compressed with PEPTO look like? The file PEP.LZH, included with this issue of the C News, gives a couple of examples. The program DICE.C, which was used in the command line parameters article was compressed form 1,768 bytes to 433 bytes. The compressed file, DICE.PEP, can be compared to the original file, DICE.C. With a small program like this, it is easy to look at the compressed version and see what the program is supposed to do; however, in a larger, more complex, program it is not as easy. For example, I took the program PROGRAM8.C, which I happened to have handy and compressed it with PEPTO. The resulting file is just under half as large as the original, not the 75.5% reduction I'd seen with DICE.C, but DICE.C was mainly comments. (NOTE: Just stripping the comments and left justifying the code in DICE.C produces a file of 533 bytes.) PROGRAM8.PEP is hard to read because not only are the comments missing, but there is no real structure to the program. Like the file description said, this an odd utility. As with any program, there are a couple of things to remember when using PEPTO. PEPTO will not accept *.PEP files as input. PEPTO only understands inline assembler lines which begin with "asm", don't use a command such as "#define A asm". The author, "created it for my own use (necessity is a mother!) but it is something which can benefit others so I have decided to release it as shareware." As such, a five dollar donation is requested if you find PEPTO useful. More information on PEPTO can be obtained from the author: David Stafford Research and Development 1800 Green Hills Rd. Scotts Valley, CA 95066 CIS: 72411,2670 MCI mail: DSTAFFORD. Issue 17 C News 15 ================================================================= ARTICLE SUBMISSION STANDARDS ================================================================= All articles, reviews and letters to editor should be submitted in a ASCII formatted file. Please use 0-65 margins, and single space. Do not format the text in anyway, as I use Proff to format C News. Proff takes care of the justification, footnotes and headers. You can send in your article on a diskette to the C BBS, or upload it to the C BBS. See "How to Contact us here at C News" for more information. Barry Issue 17 C News 16 ================================================================= HOW TO GET HOLD OF US HERE AT CNEWS ================================================================= The primary address for C News is as follows: C News % BCL Limited P.O. Box 9162 McLean, VA 22102 USA The primary electronic address for C News is the C BBS: C BBS 1-703-644-6478 2400,8,N,1 23hrs a day. 1:109/307 in Fidonet. The secondary electronic address for C News is: MCI Mail: BCL Limited Barry