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 / CNEWS002.ZIP / CNEWS002.NWS

Wrap

Text File | 1988-06-22 | 17.3 KB | 410 lines

Volume 1, Number 2 10 January 1988 +---------------------------------------------------------------+ | | | | | | | - C News - | | | | | | International | | C Programming & Compiler Review | | Newsletter | | | | | | | +---------------------------------------------------------------+ US Office: Editor Barry Lynch Reston, VA Foreign Office: Editor David Nugent Melbourne, Australia C News is published once a month by the C BBS as its official newsletter. You are encouraged to submit articles for publication in C News. Articles should be related to C programming and can be Tutorials, reviews or articles of interest to the C programming community. All Operating systems are fairly represented and this newsletter shows no favoritism to any one in particular. C News is the property of the C BBS and is Copyright 1988 by the the C BBS. All rights are reserved and distribution is limited to electronic distribution and personal printed copies. C News cannot be resold at any profit, by any organization. All material enclosed within the newsletter is the opinions of the writers and not the C BBS or it's Sysop. Table of Contents 1. EDITORIAL The Heap: messages from the editor.................... 1 2. BOOK REVIEWS C: The Complete Reference reviewed by Tom Leonard .............................. 2 TurboC Programmer's Reference Book reviewed by Tom Leonard .............................. 2 Crafting C Tools for the IBM PC. reviewed by Mike Shaw ................................ 3 3. ARTICLES TurboC & TSR's: A few Questions by Arnie Cherdak ......... ........................... 4 C News 1-02 Page 1 10 Jan 1988 ================================================================= EDITORIAL ================================================================= The HEAP: Messages from the Editor. Well with only one issue under my belt, the C News -letter is already expanding. David Nugent has voluntered to be a contributing editor for future issues of C News. Since David is located in Melbourne, Australia I figured that he could head the foreign office there for us. Gee, the C BBS is now international in scope. Besides, David other C BBS users are pitching in to contribute reviews, tutorials and other information to this newsletter. Three users as of this issue have contributed, with others planning to in future issues. Keep in mind that this Newletters letter is for all C programmers, and I hope that you will send in questions, articles, book reviews and sample programs that you might like to show off. Each article has the author's name included in the byline. Any comments on any of the articles should be sent to the those individuals, direct if you would like, or to the C BBS. I started an article on the "Legal Aspects of Software Design", but decided to get some legal counsel before I put anything on paper. Never fear that article will be finished by the next issue. Speaking of which the next issue is scheduled for publication two weeks from today - 17 January. If you would like to submit an article to C News, it must be here by the 14th to be included. Thanks B C'ing U.. Barry C News 1-02 Page 2 10 Jan 1988 ====================================================================== BOOK REVIEWS ====================================================================== ______________________________________________________________________ Title: C: The Complete Reference Author/s: Herbert Schildt Publisher: Osborne McGraw-Hill 2600 Tenth Street Berkeley, California 94710 ISBN #: 0-07-881263-1 If you are just starting into the C langugage you should get a copy of this book. This book tries to be the COMPLETE REFERENCE TO C and to a large extent it is. When I need to known how to use a multidimensional array or when I want a library routine that will copy a string this is the book I look in first. "C: The Complete Reference" is a large book. It is over 700 pages and it will probably take you a few weeks to read through it but it is worth the effort. _______________________________________________________________________ Title: Turbo C Programmer's Resource Book Author/s: Fredrick Holtz Publisher: TAB books Inc P.O. Box 40 Blue Ridge Summit, PA 17214 ISBN #: 0-8306-3030-9 If you are not sure of the differents between a string and a character array or if the following line of codes makes your eyes cross int x=0; while((a[x] += (a[x]>='A' && a[x]<='Z') ? ' ':0)) ++x; Then this books should help quite a bit. While the title says TURBO C the book will be of value with any C compiler. It very gently and carefully explains the C languages. This is not a complete reference to C but is an excellent tutorial for someone just starting into the languages. Hint: The above code converts the lower case letters in a string to upper case letters. C News 1-02 Page 3 10 Jan 1988 ====================================================================== BOOK REVIEWS ====================================================================== ______________________________________________________________________ Title: Crafting C Tools for the IBM PCs Author: Joe Campbell Publisher: Prentice-Hall Software Series ISBN #: 0-13-188418-2 This book is an excellent one to read if you want to understand the internal workings of the 8086/8088 processor and MS-DOS. The author provides valuable insites into how programs are loaded and executed by DOS and how Assembler-to-C module communication occurs. Sections are included on directory structure, keyboard input handling, standard output as well as direct video access, and advanced video topics such as coding window subroutines. The last topics covered include coding your own interrupt handling routine and serial communication processor. Despite its title, this book is almost one-third Assembler routines. Many Assembler and C routine examples are included; the examples are built up chapter-to-chapter, eventually resulting in a sophisticated directory listing program. A section is included on C compiler differences, memory model considerations for C programs, and the complete 8086 instruction set. I recommend this book to anyone who wants to use C and Assembler to write DOS utility programs. _____________________________________________________________________ C News 1-02 Page 4 10 Jan 1988 ====================================================================== TurboC and TSR's by Arnie Cherdak.. ====================================================================== It is unfortunate that Borland's documentation of their INTERRUPT type function is rather sketchy. Certain features appear to be a mystery and I wanted to share some of the insights I have had. My problem related to the code generated by the Turbo C compilers. INTRODUCTION An interrupt service routine (ISR) terminates with an "iret" assembly language instruction. The difference between this and a regular "ret" instruction used to return from a regular function call is shown below. CPU Action Instructions>>> ret far ret iret pop instruction pointer value YES Y Y pop code segment value NO Y Y pop flags N N Y Functions compiled in the Tiny, Small, and Compact models would use the "ret" instruction since they have <= 64K of code. Medium, Large, and Huge model functions would use the far ret instruction to allow function calls beyond the 64K limit. The values on the stack get there through the normal action brought about by the instructions used to get to the functions. A simple call within a 64K segment causes the instruction pointer to be pushed onto the stack while a far call causes the code segment value to be added. Indirect calls are a bit different but result in the same stack configuration. An interrupt service routine is executed through an "int" instruction which causes the flags, segment, and instruction pointer to be pushed on the stack before the CPU is sent off to execute the routine. OBSERVATION I recently bought Al Stevens' book, "Turbo C -- Memory-Resident Utilities, Screen I/O and Programming Techniques." In my opinion, he has written an exceptionally clear and understandable text and has produced a fine bit of programming that works extremely well. He has my congratulations on a job well done. In going through Stevens' code for interrupt type functions, I saw that he invokes ISR's within those functions with simple function calls and apparently without accomodation for the iret instruction that must appear at the exit point of the ISR. An example: C News 1-02 Page 5 10 Jan 1988 ====================================================================== TurboC and TSR's by Arnie Cherdak.. ====================================================================== /*************************************************************** QUEST.C -- Test program to examine ISR return code ****************************************************************/ #include <stdio.h> #define intnum 0x16 void interrupt (*oldisr)(); /* prototype and declaration of oldisr */ /* which is a variable declared as a */ /* pointer to an interrupt function. */ void interrupt newisr() /* new isr is executed each time */ { /* interrupt intnum is executed */ (*oldisr)(); } main() /* saves old isr vector & installs new */ { oldisr = getvect(intnum); setvect(intnum,newisr); } /******************** End of Quest.c **************************/ Here, the value of the vector for interrupt, intnum, is retrieved and saved and it is then replaced with a vector pointing to the new isr, "newisr." OK so far! Here's where my understanding goes to pot. The new isr calls the old isr which is a construct Stevens uses quite frequently although there is generally other code within the new isr as might be expected. I left it out here to simplify matters. Now regardless which memory model is applied here, it seems that the function call to oldisr should result in a far call instruction being pushed onto the stack by Turbo C and, as I know from my travels through the BIOS listings, oldisr invariably returns with an iret. It seems that the thing should blow up with the stack underflowing almost immediately but it doesn't. It works just fine. C News 1-02 Page 6 10 Jan 1988 ====================================================================== TurboC and TSR's by Arnie Cherdak.. ====================================================================== Obviously, I missed something. The Turbo C manuals don't clarify this or even seem to mention it. TC must make an accomodation for the type of the called isr vector but I was baffled. Anybody have any insights to share? I'm going to compile the above example using the TCC switch to yield an assembly language output. I should be able to see what's happening from that. /***************** TIME PASSES *********************************/ THE ANSWER Well, I used the "-S" switch on TCC, the command line compiler, and I got my answer. As you can see from the resulting assembly language output below, Turbo C inserts a "pushf" instruction ahead of the call to "oldisr" which causes the flags to be pushed onto the stack. Next, notice that the call to oldisr is an indirect call using the value of the vector to oldisr stored in memory. In effect, Turbo C has circumvented the effects of the compilation memory model type by using the pushf and the indirect call which created a stack configuration exactly like that produced by an "int" instruction and allowed the "iret" in the oldisr to execute without bombing the system. MYSTERY SOLVED!!! ;===================================================================== ; ; ASSEMBLY LANGUAGE OUTPUT FROM TCC FOR COMPILATION OF ; ISR ROUTINE, QUEST.C ; ;===================================================================== name quest _TEXT segment byte public 'CODE' DGROUP group _DATA,_BSS assume cs:_TEXT,ds:DGROUP,ss:DGROUP _TEXT ends _DATA segment word public 'DATA' _d@ label byte _DATA ends _BSS segment word public 'BSS' _b@ label byte _BSS ends _TEXT segment byte public 'CODE' ; Line 11 _newisr proc far push ax push bx push cx push dx push es push ds push si push di push bp mov ds,cs:DGROUP@ C News 1-02 Page 7 10 Jan 1988 ====================================================================== TurboC and TSR's by Arnie Cherdak.. ====================================================================== ; Line 12 pushf ; <============== LOOK HERE!!!!! call dword ptr DGROUP:_oldisr ; <============== Turbo C Did It! ; Line 13 @1: pop bp pop di pop si pop ds pop es pop dx pop cx pop bx pop ax iret _newisr endp ; Line 16 _main proc near ; Line 17 mov ax,22 push ax call near ptr _getvect pop cx cwd mov word ptr DGROUP:_oldisr+2,dx mov word ptr DGROUP:_oldisr,ax ; Line 18 mov ax,offset _newisr mov dx,cs push dx push ax mov ax,22 push ax call near ptr _setvect add sp,6 ; Line 19 @2: ret _main endp _TEXT ends _BSS segment word public 'BSS' public _oldisr _oldisr label dword db 4 dup (?) _BSS ends _DATA segment word public 'DATA' _s@ label byte _DATA ends _TEXT segment byte public 'CODE' extrn DGROUP@:word extrn _setvect:near public _newisr public _main extrn _getvect:near _TEXT ends end