pls help me to fix the issue

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Hi,

i am doing code under UNICODE environment in vc++.

i am trying to read the registry values

DWORD aType = 0;
DWORD aSize = 0;
LPTSTR aBuffer = NULL;
RegQueryValueEx(hTestKey, L"DisplayName" , NULL, &aType, NULL, &aSize);
aBuffer = (char *)malloc(sizeof(char)*aSize);

I got the following error..

CSS

error C2440: '=' : cannot convert from 'char *' to 'unsigned short *'
Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

how to solve it.

Posted 1-Apr-12 23:28pm

@BangIndia

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3 solutions

Solution 3

//LPTSTR aBuffer = NULL;

Declaring the aBuffer as a char* will solve the issue.

Try char* aBuffer = NULL;

Posted 3-Apr-12 9:08am

stewens

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CPallini · Accepted Answer · 2012-04-02T00:02:00

Solution 2

aimdharma wrote:
LPTSTR aBuffer = NULL;
//...
aBuffer = (char *)malloc(sizeof(char)*aSize);

You should use types consistently: namely a LPTSTR is a pointer to TCHAR, hence:

C++

LPTSTR aBuffer = NULL;
//...
aBuffer = (TCHAR *) malloc(sizeof(TCHAR) * aSize);

[update]

As correctly noted by nv3, you need a buffer of exactly aSize bytes in order to call RegQueryValueEx, hence the correct allocation is:

C++

aBuffer = (TCHAR *) malloc(aSize);

[/update]

Posted 2-Apr-12 0:02am

CPallini

Updated 2-Apr-12 10:09am

v2

Comments

@BangIndia 2-Apr-12 6:03am

Thanks a lot..

CPallini 2-Apr-12 6:42am

You are welcome.

nv3 2-Apr-12 13:59pm

Actually, this solution is not fully correct. The malloc allocates twice as much storage as is really needed. RegQueryValueEx explicitly asks for a BYTE buffer and returns always the number of bytes that it needs, not the number of characters! So

malloc (aSize)

is what is needed. I therefore would recommend to stick with the data type that RegQueryValueEx asks for. Then, after testing the aType return value, you would want to cast the buffer pointer into whatever type the system call has returned -- in case of a string into a PTSTR.

CPallini 2-Apr-12 15:48pm

Yes, you are right.

Espen Harlinn 2-Apr-12 16:24pm

5'ed!

CPallini 3-Apr-12 3:42am

Thank you.

nv3 · Accepted Answer · 2012-04-01T23:45:00

Solution 1

The auxiliary buffer is expected to be an array of bytes. So that is what you should provide. Your definition of a Buffer as LPTSTR translates in a Unicode build to a wchar_t* and your char* cannot be cast into that. So do it this way:

BYTE* aBuffer = NULL;
...
aBuffer = (BYTE*) malloc (aSize);

Posted 1-Apr-12 23:45pm

nv3

Comments

nv3 2-Apr-12 14:05pm

Hello aimdharam!

In a message message that meanwhile obviously has been removed you wrote that this solution was not correct and you would still get a compile error

*** cannot convert from 'unsigned char *' to 'unsigned short *'

Could it be that you have not copied the first line of the above code, in which aBuffer is being declared as BYTE* ? You have probably used your original declaration of

LPTSTR aBuffer = NULL;

didn't you? I would always prefer to declare the buffer as BYTE*, because that is what the system call asks for. Using any other type might easily get you confused about the number of bytes to allocated, as you can see in the solution 1 example.

Espen Harlinn 2-Apr-12 16:24pm

5'ed!