Windows SDK Registry: How can I read data from the registry?
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Thread: Windows SDK Registry: How can I read data from the registry?

  1. #1
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    May 2000
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    Posts
    18,652

    Windows SDK Registry: How can I read in data from the registry?

    Q: How can I read data from the registry?

    A:

    Code:
    HKEY  hKey;
    DWORD dwSize     = 0;
    DWORD dwDataType = 0;
    DWORD dwValue    = 0;
    
    if(::RegOpenKeyEx(HKEY_LOCAL_MACHINE,
                      "System\\CurrentControlSet\\Control\\Windows",
                      0,
                      KEY_QUERY_VALUE,
                      &hKey) == ERROR_SUCCESS)
    {
      // Get CSD version
      dwSize = sizeof(dwValue);
    
      if(::RegQueryValueEx(hKey,
                           "CSDVersion",
                           0,
                           &dwDataType,
                           reinterpret_cast<BYTE *>(&dwValue),
                           &dwSize) != ERROR_SUCCESS)
      {
        // Close key
        ::RegCloseKey(hKey);
    
        // Error handling
      }
      else
      {
        // Work with value
        // Close key
        ::RegCloseKey(hKey);
      }
    }
    else
      // Error handling;
    Last edited by Andreas Masur; July 25th, 2005 at 04:11 PM.

  2. #2
    ovidiucucu's Avatar
    ovidiucucu is offline Moderator/Reviewer Power Poster
    Join Date
    Feb 2003
    Location
    Iasi - Romania
    Posts
    8,059

    Re: Windows SDK Registry: How can I read data from the registry?

    Q: The RegQueryValueEx function returns an error code 234 (ERROR_MORE_DATA) that means "more data is available". How many bytes must be allocated for value buffer to assure this error does not appear anymore?

    A: To find the necessary buffer size, call 'RegQueryValueEx()' with a 'NULL' value in 'lpData' parameter. After return, the variable pointed by 'lpcbData' will contain the size of the data. Allocate the buffer 'lpData' then call 'RegQueryValueEx()' again:

    Code:
       HKEY  hKey       = NULL;
       DWORD dwSize     = 0;
       DWORD dwDataType = 0;
       LPBYTE lpValue   = NULL;
       LPCTSTR const lpValueName = _T("Directory");
    
       LONG lRet = ::RegOpenKeyEx(HKEY_LOCAL_MACHINE,
                                  _T("System\\CurrentControlSet\\Control\\Windows"),
                                  0,
                                  KEY_QUERY_VALUE,
                                  &hKey);
       if(ERROR_SUCCESS != lRet)
       {
          // Error handling (see this FAQ)
          return;
       }
       // Call once RegQueryValueEx to retrieve the necessary buffer size
       ::RegQueryValueEx(hKey, 
                         lpValueName,
                         0,
                         &dwDataType,
                         lpValue,  // NULL
                         &dwSize); // will contain the data size
    
       // Alloc the buffer
       lpValue = (LPBYTE)malloc(dwSize);
    
       // Call twice RegQueryValueEx to get the value
       lRet = ::RegQueryValueEx(hKey, 
                                lpValueName,
                                0,
                                &dwDataType,
                                lpValue,
                                &dwSize);
       ::RegCloseKey(hKey);
       if(ERROR_SUCCESS != lRet)
       {
          // Error handling
          return;
       }
       // Enjoy of lpValue...
       // free the buffer when no more necessary
       free(lpValue);
    Last edited by Andreas Masur; July 25th, 2005 at 04:12 PM.

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