C / C++ / MFC

LPTSTR, LPCTSTR, CString and others...

15-Jul-04 11:23

You need to redraw after all those situations (covering, minimizing etc..).. Why couldn't you use your drawing routine in the WM_PAINT handler?

Rob

Whoever said nothing's impossible never tried slamming a revolving door!

Kaleb Pederson15-Jul-04 9:22

Kaleb Pederson

15-Jul-04 9:22

I'm new to Windows programming (not C/C++) and I'm having a hard time with all of the different string facilities. For example, I wanted to do a simple registry read, so I tried:

LPCTSTR strEntry = _T("SOFTWARE\\Microsoft\\...path...");
LPTSTR val;
ULONG max_size = 1024;
if ((retval = rc->QueryStringValue(strEntry,val,&max_size)) != ERROR_SUCCESS) { /* an error occurred */ ... }

Which dies. Apparently LPTSTR needs to be allocated, but I don't need an array of them (as one might with chars) so that wouldn't help.

I found a bunch of documentation on converting strings of various types, but I'd like to allocate one.

Thanks for the help.

Toni7815-Jul-04 9:40

Toni78

15-Jul-04 9:40

You have to allocate memory for LPTSTR data types. LPTSTR is a pointer of type TCHAR, which in turn is a wchar_t. What is it exactly that you are trying to accomplish?
Maybe by declaring:
TCHAR val[SomeNumberHere];
might help you. I am not sure what you want to do.

// Afterall, I realized that even my comment lines have bugs

If the sun were to blow up, it would take us 7-8 minutes to realize it.

Adam Durity15-Jul-04 9:49

Adam Durity

15-Jul-04 9:49

LPTSTR is a pointer to a string, so if you don't initialize it, it doesn't mean anything. Just saying

LPTSTR val;

is not enough, because then it would get allocated and point to some random memory location. You then must specify where it points to so that in your call to QueryStringValue() it has a referenced location to store the string.

One way to do this might be

LPCTSTR strEntry = _T("SOFTWARE\\Microsoft\\...path...");
TCHAR val[1024];
ULONG max_size = 1024;
if((retval = rc->QueryStringValue(strEntry, val &max_size)) != ERROR_SUCCESS
{
// error handling
}

in this you are allocating an array to hold the string, then, you can assign it to a CString.

CString str = val;

Essentially the TCHAR array is a buffer of known length max_size. You use this buffer to collect the value string. Also, it should be noted that in the above example, you can use a CString instead of the LPCTSTR.

-- Adam

"If you can't beat your computer in chess, try kickboxing"

Antti Keskinen15-Jul-04 9:53

Antti Keskinen

15-Jul-04 9:53

The trick here is to 'understand' what these Windows types are. If you searched through the Windows headers, you'd find the answers. But to make your job a little easier, here's a quickie for starters.

LPCTSTR == const TCHAR* == const char*
LPTSTR == TCHAR* == char*

If you'd needed to create a string, the idea would be to use an LPTSTR and the new-operator to allocate memory for your string.

The idea is behind the ability to use the same variable types regardless of whether Unicode or ASCII/MBCS is in effect. For example, the following would use pure-Windows methods to initialize, utilize and destroy a string of characters, regardless of used character set:

_TCHAR* strName = new _TCHAR[20];
ZeroMemory(strName, SIZEOF(TCHAR) * 20);
_tcsncpy( strName, _T("My name is"), _tcsclen(_T("My name is")) );
delete strName;

As you can see, programming while taking the character set in mind is a tad more difficult than standard C++.

For your code sample, the problem is that LPTSTR val would map to char* val, and you, in there, pass an uninitialized pointer to the function. No wonder it crashes Big Grin | :-D

To play safe, use the new-operator to initialize say 50-60 characters, and pass this pointer to the function. Should work smoothly.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

Kaleb Pederson15-Jul-04 11:25

Kaleb Pederson

15-Jul-04 11:25

Thanks. That was a great help and I was able to get it working.

In what header should I be able to find the typedefs? I looked at "Windows Data Types" and now that I know, I can see how I could have determined that it was a char* (with _UNICODE not defined), but I would love to know where most things are going to be defined.

Antti Keskinen15-Jul-04 11:50

Antti Keskinen

15-Jul-04 11:50

Most of the character mappings can be found from 'winnt.h' file.

-Antti Keskinen

----------------------------------------------
The definition of impossible is strictly dependant
on what we think is possible.

PJ Arends15-Jul-04 17:14

PJ Arends

15-Jul-04 17:14

If you want to know where something is defined, right click on it and select "Go to definition" from the popup menu.

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

Within you lies the power for good - Use it!

Mike Dimmick15-Jul-04 9:58

Mike Dimmick

15-Jul-04 9:58

Couple of links:

The complete guide to C++ strings, part I[^]
The complete guide to C++ strings, part II[^]

Basically, LPxSTR is a typedef for xCHAR*, i.e. LPTSTR is a typedef for TCHAR*, LPSTR for CHAR*, and LPWSTR for WCHAR*. If it has a C in it, it's a const: LPCSTR is const CHAR*.

So what are CHAR, WCHAR and TCHAR? CHAR is simply a typedef for char. Don't know why they did that. WCHAR is a typedef for wchar_t which on earlier compilers is a typedef for unsigned short.

TCHAR is where it gets interesting. The meaning of TCHAR depends on whether UNICODE is defined or not. If UNICODE is not defined, TCHAR is CHAR. If UNICODE is defined, TCHAR is WCHAR. With the addition of suitable macros (such as the _T you use) a program can be mostly adapted between ANSI and UNICODE builds with few source code changes.

Anyway, after all that, LPTSTR is equivalent to WCHAR* in UNICODE builds and char* in ANSI builds. Use whatever memory allocation seems appropriate.

Stability. What an interesting concept. -- Chris Maunder

IJolietDiscMaster & Joliet & Invalid Naming Convention

digwizfox15-Jul-04 11:07

digwizfox

15-Jul-04 11:07

Thanks, those articles are really interesting. I learned a lot of this stuff the hard way using the MSDN documentation which is pretty good but you really have to search and easily get caught going in circles trying to understand it. You're explanation was the best out of what I read of the responses to the original question. In the MSDN they have some nice charts that show how the typedefs and C run time functions map, depending on whether _UNICODE is defined. Do a search on TCHAR in the MSDN libary index and you'll see links to the mapping charts there and will probably find many other wild goose chases that will contain a wealth of info on the concept of the TCHAR family. Not only are there many data type mappings but there is a whole family of mappings for the C run time string functions as well. The whole purpose is to support character set neutral code, which is something else you'll learn about in the MSDN documentation.

abt running exe

jass198115-Jul-04 9:20

jass1981

15-Jul-04 9:20

hai,
I'm using win32 appln.While executing my appln (say a dialog) if again I execute my appln another exe starts.How to prevent this.I want only one exe to run at a time.Can anyone help?
thanks a lot in advance.

Re: abt running exe

Toni7815-Jul-04 9:42

Toni78

15-Jul-04 9:42

Take a look at http://www.codeproject.com/cpp/avoidmultinstance.asp[^]

// Afterall, I realized that even my comment lines have bugs

If the sun were to blow up, it would take us 7-8 minutes to realize it.

Re: abt running exe

PJ Arends15-Jul-04 9:47

PJ Arends

15-Jul-04 9:47

Do a search for "single instance" and you will get a lot of articles explaining how to.

"You're obviously a superstar." - Christian Graus about me - 12 Feb '03

"Obviously ??? You're definitely a superstar!!!" mYkel - 21 Jun '04

Within you lies the power for good - Use it!

Re: abt running exe

Paul Steane16-Jul-04 1:33

Paul Steane

16-Jul-04 1:33

The best I've found on this subject is by Joseph M. Newcomer at http://www.flounder.com/nomultiples.htm[^]

epxhi15-Jul-04 9:10

epxhi

15-Jul-04 9:10

I'm doing a cd burning app using IJolietDiscMaster. For some reason it only works when the filename to be burn to the cdrom does not contain a directory.

// IStorage accepts this file
thisisokay.exe

// IStorage rejects this file

\\Directory\\on\\CD\\thisisokay.exe

Also, IStorage rejects creating multiple layers directory

// IStorage accepts this directory

Thisisokay

// IStorage rejects this directory

\\Directory\\on\\CD\\

What is wrong with the naming convention i'm passing into IJolietDiscMaster's AddData()?

Thank you!

Dumb loop question.

RobJones15-Jul-04 9:03

15-Jul-04 9:03

For some reason I'm having a major brain fart.. I am trying to write a simple loop to read 32 chars at a time from a CString and feed them to a function.. Can someone give me some help.

CString strFart = "some really long string over 500 chars";
int nLen = strFart.GetLength();

while((nLen/32) > 0)
{
// Need to feed a TCHAR function
// 32 chars at a time from strFart;
nLen - 32;
}

Should I be using the CString::mid function?

Rob

Whoever said nothing's impossible never tried slamming a revolving door!

palbano15-Jul-04 9:19

palbano

15-Jul-04 9:19

RobJones wrote:
Should I be using the CString::mid function?

That would work. Did you try it? What happened?

"No matter where you go, there your are." - Buckaroo Banzai

-pete

RobJones15-Jul-04 9:24

15-Jul-04 9:24

I can get it to work but it looks really ugly.

Whoever said nothing's impossible never tried slamming a revolving door!

palbano15-Jul-04 9:30

palbano

15-Jul-04 9:30

RobJones wrote:
I can get it to work but it looks really ugly.

Run it through the Hollywood translator engine and see if that improves it's looks. Be warned, while it may be better looking, the behavior might seem a bit queer. Laugh | :laugh:

"No matter where you go, there your are." - Buckaroo Banzai

-pete

RobJones15-Jul-04 9:50

15-Jul-04 9:50

ROFLMAO.... Big Grin | :-D

Whoever said nothing's impossible never tried slamming a revolving door!