convert from 'char *' to 'LPCWSTR'

[mexicaan]

Hi,

I am a total noob at c++.

I have the following code:

   CoInitialize (NULL);

   HRESULT hr;
   IActiveDesktop *pActiveDesktop;
   char* wpurl;

   wpurl = GrabTextFromEdit(IDE_WPURL);
   hr = CoCreateInstance(CLSID_ActiveDesktop, NULL, CLSCTX_INPROC_SERVER, IID_IActiveDesktop, (void**)&pActiveDesktop);
   //OLECHAR szFile [] = OLESTR(wpurl);
   hr = pActiveDesktop->SetWallpaper(wpurl, 0);

   pActiveDesktop->ApplyChanges(AD_APPLY_ALL);
   pActiveDesktop->Release();

   MessageBox(m_hWnd, "The wallpaper has been changed", "",MB_OK);
   return true;

When i run this code i get this error:
error C2664: 'IActiveDesktop::SetWallpaper' : cannot convert parameter 1 from 'char *' to 'LPCWSTR'

So i have tried to covert the wpurl variable to a LPCWSTR with the mbstowcs function but couldnt figure out how to implement it.

Can anyone help me to covert the character?

Thanks alot i advnance

[golanshahar]

try this:

char* wpurl;
wpurl = GrabTextFromEdit(IDE_WPURL);

if ( wpurl )
{
  int len = strlen(wpurl)+1;
  wchar_t *wText = new wchar_t[len];
  if ( wText == 0 )
    return;
  memset(wText,0,len);
  ::MultiByteToWideChar(  CP_ACP, NULL,wpurl, -1, wText,len );

  //now pass wText
  hr = pActiveDesktop->SetWallpaper(wText, 0);

  
  // when finish using wText dont forget to delete it
  delete []wText;

}

Cheers

[mexicaan]

Worked perfectly, thank you

[Yves M]

Actually this can lead to memory corruption if your string is longer than MAX_PATH characters. For a better way, and more explanations, check out this FAQ

[golanshahar]

Actually this can lead to memory corruption if your string is longer than MAX_PATH characters. For a better way, and more explanations, check out this FAQ

Yup, you are right, good point,

i fixed the code.

Cheers

[Yves M]

That's actually not always correct either. The length of the multi-byte string is not always the same as the 8-bit string, because the 8-bit string may not be ASCII (but e.g. UTF-8, etc.) So this solution only works with codepages which map 1 character to 1 character in Unicode.

Check the second part of the FAQ for that.

[humptydumpty]

hr = CoCreateInstance(CLSID_ActiveDesktop, NULL,
CLSCTX_INPROC_SERVER, IID_IActiveDesktop, (void**)
&pActiveDesktop);
//OLECHAR szFile [] = OLESTR(wpurl);
hr = pActiveDesktop->SetWallpaper(wpurl, 0);

Before calling your method mean to say at the time when u used ::CocreateInstance.you should check whether function succeed or not after that only gave a call to your com function

hr = CoCreateInstance(CLSID_ActiveDesktop, NULL, 
CLSCTX_INPROC_SERVER, IID_IActiveDesktop, (void**)
&pActiveDesktop);
if(SUCCEEDED(hr))
  //call your SetWalpaper function now.

try this:

 
char* wpurl;
wpurl = GrabTextFromEdit(IDE_WPURL);

Cheers

when ever declare a pointer .u should initialize it other wise u are going to get some big problem.

Second thing whenever u used new to allocate memory .i think u should initialize it with memset so proper initialization can take place because new allocate memory for you.but initialization doesn't take place in this case.which is some time going to gave problem.

[golanshahar]

when ever declare a pointer .u should initialize it other wise u are going to get some big problem.

basically you are right however in this code the second line after declaring the pointer it is being set to a value returned from the

GrabTextFromEdit(IDE_WPURL);

which btw i dont know what it is cause its OP function.
so even if i would set it to 0 second line its value would have changed.

Second thing whenever u used new to allocate memory .i think u should initialize it with memset so proper initialization can take place because new allocate memory for you.but initialization doesn't take place in this case.which is some time going to gave problem.

well i am doing it...look again in the code

Cheers

[humptydumpty]

yes u r using for wtext but not for wpurl.and i am saying in case of wpurl and if u decalre a simple pointer in c++ and just check it out .mean to say without initialize just try to put some value in the pointer u r going to get exception. that's all

[Attalian]

Hi i have that code it works on DevCpp but in Visual Studio gives error.

//______________________________________________

#include <cstdio> // getchar()
#include <iostream>
#include <windows.h> // PlaySound()

#define SND_FILENAME 0x20000 // from mmsystem.h
#define SND_LOOP 8
#define SND_ASYNC 1
#define SND_ALIAS 0x10000

int main()
{
char sound[] = "C:/ohhnooo.wav";

PlaySound(sound,NULL,SND_FILENAME|SND_ASYNC);

getchar();

return 0;
}

//______________________________________________


The Error is :
error C2664: 'PlaySoundW' : cannot convert parameter 1 from 'char [15]' to 'LPCWSTR'

What is the problem? :/

[Zaccheus]

A general note:


Many COM functions take a BSTR, not a LPCWSTR, and BSTRs need to be allocated using SysAllocString and are freed using SysFreeString .

[TheCPUWizard]

A general note:


Many COM functions take a BSTR, not a LPCWSTR, and BSTRs need to be allocated using SysAllocString and are freed using SysFreeString .

And both operations need to take place within the same context. (i.e. You can not Alloc from one heap, and Free to a different heap).

[abcdefgqwerty]

I feel your pain on string conversions. c++ overly complicates strings. They have a string class, but it doesnt actually convert all string types from and to every other type. I dont understand why converting strings is the huge pain it is unless its just me not understanding why there are 10 different types of strings.

[Yelior]

Greetings everyone, I have a problem, I'm just starting to work with Ogre Visual Studio 2005 and I have a problem with a conversion of a char * THIS CODE LPCWSRT ... ....


int main(int argc, char **argv)
#endif
{
// Create application object
TutorialApplication app;

try
{
app.go();
}
catch( Exception& e )
{

#if OGRE_PLATFORM == PLATFORM_WIN32 || OGRE_PLATFORM == OGRE_PLATFORM_WIN32
MessageBox(NULL, e.getFullDescription().c_str(), "An exception has occurred!", MB_OK | MB_ICONERROR | MB_TASKMODAL);

#else
fprintf(stderr, "An exception has occurred: &#37;s\n",
e.getFullDescription().c_str());
#endif
}

return 0;
}

and this is the error I get ...

error C2664: 'MessageBoxW' : cannot convert parameter 2 from 'const char *' to 'LPCWSTR'
Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast

[Speedo]

http://www.ogre3d.org/wiki/index.php...ge_Box_Trouble