Re: LPCTSTR and HRESULT - C / C++ / MFC Discussion Boards

George_George26-Jul-07 21:44

26-Jul-07 21:44

Thanks Shilpi,

I do not know it is const before, so I can not change the value of the string, right?

What means long pointer (for 1st letter L in LPCTSTR)?

regards,
George

Re: LPCTSTR and HRESULT

Shouvik Das26-Jul-07 23:58

Shouvik Das

26-Jul-07 23:58

<big>Acronym     Definition</big>
LPCTSTR          Long Pointer to a Constant null-Terminated String

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: LPCTSTR and HRESULT

George_George27-Jul-07 20:20

George_George

27-Jul-07 20:20

Thanks shouvik,

Long pointer means? What is the difference between long pointer and a normal pointer?

regards,
George

Re: LPCTSTR and HRESULT

Iain Clarke, Warrior Programmer27-Jul-07 1:29

Iain Clarke, Warrior Programmer

27-Jul-07 1:29

The L bit is a historical hangover from 16 bit windows - it no longer has any extra meaning, but as the function prototypes for windows use it, it was kept on.

There used to be near and far pointers in the old days... sigh, segments....

Iain.

ps, I don't miss this old days, either!

Re: LPCTSTR and HRESULT

George_George27-Jul-07 20:21

George_George

27-Jul-07 20:21

Thanks Iain,

For 32-bit or 64-bit machine, I do not need to consider it, right?

regards,
George

Re: LPCTSTR and HRESULT

Shouvik Das29-Jul-07 18:37

Shouvik Das

29-Jul-07 18:37

Yeah of course. Pointers are very specifically address holders. The size of the pointers are dependent on the compiler too. While developeing 64Bit Applications the size of default pointer is 64.

Take this as a thunb rule. All sizeof are never constant-> they vary as per the compilers they are used in. If int is 2 byte in TurboC++ 3.0 it will be 4Bytes in VC++... Hope u can undestand my point.

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: LPCTSTR and HRESULT

George_George29-Jul-07 18:55

George_George

29-Jul-07 18:55

Thanks shouvik,

I want to confirm your point that data type LPCTSTR works for both 32-bit and 64-bit transparently? Means developer could use the unified data type LPCTSTR without considering whether working on 32-bit or 64-bit platform safely?

regards,
George

Re: LPCTSTR and HRESULT

Shouvik Das29-Jul-07 19:13

Shouvik Das

29-Jul-07 19:13

That is really a novel idea. But upto my knowledge (which is bit of a dumb kind Wink | ;)

) all 64 bit OS handle 32 bit data safely. I mean there is a back compatibility available which would allow safe usage without any data loss. I think they do padding and all to convert the 32 bit data to 64 bit.

If you really want to see if LPCTSTR works fine with both 64 bit and as well 32 bit transparently then develop an Appl in 32 bit compiler and then try executing it in 64 bit. I am a bit vague about further details regarding 32 bit and 64 bit compatibility issues.

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: LPCTSTR and HRESULT

George_George29-Jul-07 19:18

George_George

29-Jul-07 19:18

It is ok. Thanks for your support for all the help you given to me on the question all the way.

regards,
George

Re: LPCTSTR and HRESULT

Shouvik Das29-Jul-07 19:22

Shouvik Das

29-Jul-07 19:22

George_George wrote:
Thanks for your support for all the help you given to me on the question all the way.

That is the spirit @ CP and that is what makes my day happier while spending my day here. We all come back for a reason.

Actually one more thing to say is that LPCTSTR is strictly a Win32 stuff so please investigate it's memory implications then only proceed.In case you get to know some APIs which are translating 32 to 64 bit please share with us too.

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: LPCTSTR and HRESULT

Shouvik Das29-Jul-07 19:31

Shouvik Das

29-Jul-07 19:31

throwing some more light
http://www.codeproject.com/script/comments/forums.asp?msg=2153729&forumid=1647#xx2153729xx[^]

There are only two kinds of people who are really fascinating-people who know absolutely everything, and people who know absolutely nothing.
Oscar Wilde (1854-1900)
Regards...
Shouvik

Re: LPCTSTR and HRESULT

George_George29-Jul-07 19:46

George_George

29-Jul-07 19:46

Thanks, good link!

regards,
George

Access Violation problem

p_26-Jul-07 18:23

26-Jul-07 18:23

please tell me
what this problem means in connection of vc++ and mysql
inhandled exception myprojectname.exe(LIBMYSQL.DLL) 0xC0000005: Access Violation

please help me to solve this problem

thanks Rose | [Rose]

Re: Access Violation problem

Jonathan [Darka]26-Jul-07 20:54

Jonathan [Darka]

26-Jul-07 20:54

It means you have a bug in your code, why not try the debugger ?

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_26-Jul-07 21:08

26-Jul-07 21:08

thanks for reply sir
i use debugger and debugger shows this error in msgbox
and my code is as sir :
int i;
MYSQL *myDB;
MYSQL_RES *res;
MYSQL_ROW row;
CString user,pass,aqp;
if ((myDB = mysql_init((MYSQL*) 0)) &&
mysql_real_connect(myDB,"localhost","root",NULL,NULL,3306,NULL,NULL))

{
if ( mysql_select_db( myDB,"gourav") < 0 )
{
MessageBox("Can't select the database !\nTry later.");
goto exit_here;
}
else
{
MessageBox("Can't connect !\nPlease try later.") ;
goto exit_here;
}
}
GetDlgItemText(IDC_USER,user);
GetDlgItemText(IDC_PASS,pass);
if(mysql_query(myDB,"select * from login"))
res=mysql_store_result(myDB);
row = mysql_fetch_row(res);
MessageBox(row[0]);

exit_here:
mysql_close( myDB);

please sir help me to solve this one
thanks again

Re: Access Violation problem

Jonathan [Darka]26-Jul-07 21:20

Jonathan [Darka]

26-Jul-07 21:20

No problem, does the debugger indicate which line might be cusing the access violation ?

Try changing the code a little as your error handling could be improved, I rewrote it like this, but obviously have not tested it, so give it a go and see if that improves anything.

int i;
MYSQL *myDB = NULL;
MYSQL_RES *res = NULL;
MYSQL_ROW row;
CString user,pass,aqp;

if((myDB = mysql_init((MYSQL*) 0)) &&
mysql_real_connect(myDB,"localhost","root",NULL,NULL,3306,NULL,NULL))
{
    if(mysql_select_db( myDB,"gourav"))
    {
        GetDlgItemText(IDC_USER,user);
        GetDlgItemText(IDC_PASS,pass);

        if(mysql_query(myDB,"select * from login"))
        {
            res=mysql_store_result(myDB);
            row = mysql_fetch_row(res);
            MessageBox(row[0]);
        }
    }
    else
        MessageBox("Can't connect !\nPlease try later.") ;

    mysql_close(myDB);
}

regards,

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_26-Jul-07 22:16

26-Jul-07 22:16

thanks sir
sir i try this one but it does not work
as same error at line

row = mysql_fetch_row(res);
before this same error at same line
thanks

Re: Access Violation problem

Jonathan [Darka]26-Jul-07 22:19

Jonathan [Darka]

26-Jul-07 22:19

What is the value of 'res' when this line is executed, you'll need to strp through the code in your debugger.

res=mysql_store_result(myDB);

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_26-Jul-07 22:31

26-Jul-07 22:31

sir after debugging :
myDB shows this value 0x00ba4008
and res shows this 0x00000000
thanks.

Re: Access Violation problem

Jonathan [Darka]26-Jul-07 23:07

Jonathan [Darka]

26-Jul-07 23:07

I suspect the call is failing, have you tried adding mysql_error() to see if you get an error.

Also, change this part of the code:

if(mysql_query(myDB,"select * from login"))
{
    res=mysql_store_result(myDB);
    row = mysql_fetch_row(res);
    MessageBox(row[0]);
}

to this:

<pre
if(mysql_query(mydb,"select *="" from="" login"))
{
="" res="mysql_store_result(myDB);
" if(res)
="" {
="" row="mysql_fetch_row(res);
" if(row="" !="FALSE)
" messagebox(row[0]);
="" }
}<="" pre="">

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_26-Jul-07 23:33

26-Jul-07 23:33

yes sir i think u r right call is failing
becauze when debugger comes on if(res) it will show login window again
and this will stop debugger
but i dont know sir why this if(mysql_query(myDB,"select * from login"))
is not fetching result

[sir i use mysql 6.0 and VC++ 6.0(is there any problem Sir)]

Re: Access Violation problem

Jonathan [Darka]26-Jul-07 23:37

Jonathan [Darka]

26-Jul-07 23:37

Are there any records in the database table ?

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_26-Jul-07 23:47

26-Jul-07 23:47

yes sir
i have database gourav , a table login and
this table has three fields user , password and id
and there are three records in this table

Re: Access Violation problem

Jonathan [Darka]27-Jul-07 0:02

Jonathan [Darka]

27-Jul-07 0:02

What is the return value from the mysql_query(myDB,"select * from login")) function ?

Change it to this for a test:

int i = mysql_query(myDB,"select * from login");

What is the value of i ?

Jonathan Wilkes
Darka[Xanya.net]

Re: Access Violation problem

p_27-Jul-07 0:09

27-Jul-07 0:09

sir return value for
int i = mysql_query(myDB,"select * from login");
and i shows value 1 when use debugger

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