Category : C++ Source Code
Archive   : TI8504.ZIP
Filename : TI8503.ASC

PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 1/7

TITLE : C++ Language News, Volume 1 Number 4




_C++ Support News_
----------------------------------------------------------------
volume 1, number 4 May 10, 1993
----------------------------------------------------------------

DEBUGGING

Tracking down crash problems in a program can often be quite
elusive. One of the first things to consider in debugging is
which memory model is being used. It is far easier to crash
the machine in a large data model (compact, large, or huge) than
in a small data model (tiny, small, or medium) given that DS and
CS are restricted in the smaller models. It is common in the
small data models for crashes to come as a result of stack/heap
overflow, or stack corruption. Since the stack and heap grow

towards each other, return addresses retained on the stack can
be written over sending the CPU to an address whose contents
are certainly unknown. In the large data models, writing to a
NULL pointer will overwrite the contents of the interrupt vector
table. Writing to a bad pointer value could result in over-
writing the program's code segment or to the various internals
of the operating system.

Some of the things that should be considered in resolving this
problem is to recompile the project with all warnings turned on.
Resolve all warnings of consequence. These include "'parameter'
is never used in function 'foobar'". Messages like "non-port-
able pointer conversion" should always be resolved. Check all
heapspace requests for valid allocations by comparing the return
from operator new or function malloc() for a zero or NULL value.
Perhaps the stack size needs to be increased from its 4k default
size. If heap corruption is a possibility, place heapcheck()
function calls strategically in the code. Judicious use of
breakpoints can also isolate problem areas. With Turbo Debug-
ger, run the program with a breakpoint set for "Change Memory
Model" at address 0:0,4 to see if the beginning of the interrupt
table is being corrupted (in the small data models, this would
be meaningless due to the use of near pointers). NULL pointer
assignments are identified by the exit code re-evaluating a
checksum on the beginning of the data segment. Upon failure,
a "NULL pointer assignment" message will be given. The offender
in this case can be identified by watching DS:0,4.














PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 2/7

TITLE : C++ Language News, Volume 1 Number 4




* * * * *

Be aware that a memory leak occurs in function stat() where
memory is being allocated but not released. For customers with
Borland C++ 3.1 with Application Frameworks, this can be seen
by looking at the runtime source file
\BORLANDC\CRTL\CLIB\STAT.CAS.


DOS

1. How can TD286 be run from within a Windows DOS box? TD286
uses a VCPI memory manager while Windows 386 Enhanced mode
uses the DPMI standard for protected memory access. Since
both of these management schemes are incompatible, TD286
cannot be run under Windows in Enhanced mode. However,
Standard mode can be used effectively. Because TD286 uses
extended memory for its symbol table, a PIF file will need
to be customized for TD286. As for the specifics:

a. Start up Windows in Standard mode (using win /s).
b. Set up a PIF file that has 2000k required for ex-
tended memory. You can have the PIF file either
run TD286.EXE directly, or run COMMAND.COM from
which you can execute TD286 from the DOS prompt.


OS/2

1. If the OS2LDR.MSG file cannot be found or is unusable, error
SYS03146 is likely to be generated. This can be resolved by
replacing the current copy with the default version found on
the installation disks. In particular,
a. Boot "installation disk".
b. Install "diskette 1" when requested and press Enter.
c. At "Welcome to OS/2" screen, press Escape.
d. Insert "diskette 2" and
1. If normal harddisk boot drive is HPFS enter --
CHKDSK c: /f:3
2. If normal harddisk boot drive is FAT enter --
CHKDSK c: /f
where "c:" is the harddisk boot drive desig-
nation.













PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 3/7

TITLE : C++ Language News, Volume 1 Number 4




e. If problems were reported in step d above, reboot
OS/2 (steps a - c above).
f. Log to root of harddisk boot drive (not the floppy
boot drive) and enter --
\OS2\ATTR -h -r -s OS2LDR.MSG
g. Insert "installation disk" in floppy boot drive
(while still logged to the root of the harddisk
boot drive), and enter --
COPY A:\OS2LDR.MSG
h. After the file has been copied, enter --
\OS2\ATTRIB +r +h +s OS2LDR.MSG
i. Remove all disks from the boot floppy drive and
reboot computer.


WINDOWS

1. The following is a function that you can add to the DDEML
client example DDECLI.PRJ shipped with Borland C++ 3.1.
It uses a DDE Paste/Link convention to allow you to paste
DDE data from the clipboard.

The trick is the Clipboard format Link. By convention,
when a DDE server cuts or copies DDE data to the clipboard,
the server should also give the clipboard the service,
topic, and item names via the Link format. When a DDE
client paste/links from the clipboard, it should retrieve
the name and establish an advise loop using the names.

// add a menu choice for Paste/Link
void TDMLCIWnd::CMUPasteLink(RTMessage) {
if (OpenClipboard(HWindow)) {
// do the call
// uClipFormat = RegisterClipboardFormat("Link");
// in TDMLCIWnd::SetupWindow() or WinMain()
HANDLE hClipData = GetClipboardData(uChipFormat);
if (hClipData) {
LPSTR pClipData = (LPSTR) GlobalLock(hClipData);
if (pClipData) {
char cService[128] = "";
char cTopic[128] = "";
char cItem[128] = "";
// the data is servicename\0topicname\0itemname\0"













PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 4/7

TITLE : C++ Language News, Volume 1 Number 4




lstrcpy(cService, pClipData);
pClipData += (lstrlen(pClipData) + 1);
lstrcpy(cTopic, pClipData);
pClipData += (lstrlen(pClipData) + 1);
lstrcpy(cItem, pClipData);
GlobalUnlock(hClipData);
DdeFreeStringHandle(idInst, hszService);
DdeFreeStringHandle(idInst, hszTopic);
DdeFreeStringHandle(idInst, hszItem);
hszService = DdeCreateStringHandle(idInst,
cService, CP_WINANSI);
hszTopic = DdeCreateStringHandle(idInst,
cTopic, CP_WINANSI);
hszItem = DdeCreateStringHandle(idInst,
cItem, CP_WINANSI);
// connect to the service/topic
hConv = DdeConnect(idInst, hszService,
hszTopic, NULL);
if (hConv) {
// start the advise loop
DdeClientTransaction(NULL, 0, hConv,
hszItem, CF_TEXT,
XTYP_ADVSTART | XTYPF_ACKREQ,
1000, NULL);
HDDEDATA hData;
// force getting the data for the first time
hData = DdeClientTransaction(NULL, 0,
hConv, hszItem, CF_TEXT,
XTYP_REQUEST, 0, NULL);
// process the DDE data handle
if (hData)
ReceivedData(hData);
PostMessage(HWindow, WM_INITMENU,
(WPARAM) GetMenu(HWindow), 0);
}
}
}
CloseClipboard();
}
}


TURBO VISION













PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 5/7

TITLE : C++ Language News, Volume 1 Number 4





1. All "Uses_" definitions must occur before #include
for them to have any useful effect. Syntactically, no harm
is done by placing them after TV.H, but no use will be
served either.
2. The error message "TV needs the large memory model" will be
generated when compiling Turbo Vision applications in any
model other than the large memory model with Borland C++ 3.1
or Turbo C++ 3.0 for DOS. Earlier versions of Turbo Vision
can instead generate "Trying to derive a far class from a
near base".
3. To make a window nondraggable, put the following line in the
window's constructor --

flags &= ~wfMove;


PARADOX ENGINE

1. PROBLEM: I run my Engine 3.0 application and the call to
the constructors do not work. In particular, if I call the
BEngine constructor, it fails and lastError is
PXERR_INVALIDENGINETYPE (400). I know that I am passing a
valid constant to the constructor, but what is happening?

POSSIBLE ANSWER: The database library for the Paradox
Engine 3.0 is built with "treat enums as ints". This means
that the BEngine constructor is expecting a full twp byte
value coming in on the stack. If the project is built with-
out this switch on, the compiler will assume the size of the
BEngineType is a byte, and it will pass an argument which
the libraries constructor will not read properly. Effec-
tively, the compiler will do this:

mov al, 1 ; if we used pxLocal
push ax

which leaves garbage in the high order byte. This would be
OK if the library was expecting a byte on the stack, but be-
cause it uses a whole word, it will read the garbage from
the high order byte.


QUIZ













PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 6/7

TITLE : C++ Language News, Volume 1 Number 4




Why does the following program print out all command-line
arguments in forward versus reverse order?

#include

main(int argc, char *argv[]) {
int i = argc - 1;
while (i > -1) {
printf("%s\n", argv[i]);
i--;
}
return 0;
}


NEW TECHNICAL INFORMATION DOCUMENTS AVAILABLE

Some of the latest technical information documents available
to customers include the following.

1372 creation and use of custom records with the
Paradox Engine 3.0.
1371 creation of a single help view in Borland C++
for OS/2.
1370 explanation of various causes for spawn(),
exec(), and system() to fail in the IDE.
1369 example of changing the shadow colors in a
Turbo Vision application.
1326 provides a number of defines which can be added
to a resource file when using a later version
of BWCC.DLL (eg. BWCC.DLL from Borland Pascal
7.0). These defines allow one to access the
enhancements provided by later versions.
1307 explanation of why the max() and min() macros
are not defined within C++.
1305 description of the configuration files used by
the compiler.
1304 explanation of how to write exception handlers
for OS/2 using Borland C++ for OS/2.


These documents can be found on either LIB-2 of BCPPDOS and
BCPPWIN under CompuServe, Borland's DLBBS at (408)438-9096,













PRODUCT : Borland C++ NUMBER : 8503
VERSION : All
OS : All
DATE : May 10, 1993 PAGE : 7/7

TITLE : C++ Language News, Volume 1 Number 4




TechFAX at (800)822-4269, or OAS at (408)431-5250.



DISCLAIMER: You have the right to use this technical information
subject to the terms of the No-Nonsense License Statement that
you received with the Borland product to which this information
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