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 versiondwSize = 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;

 

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 bufferlpValue = (LPBYTE)malloc(dwSize);// Call twice RegQueryValueEx to get the valuelRet = ::RegQueryValueEx(hKey, lpValueName,0,&dwDataType,lpValue,&dwSize);::RegCloseKey(hKey);if(ERROR_SUCCESS != lRet){// Error handlingreturn;}// Enjoy of lpValue...// free the buffer when no more necessaryfree(lpValue);

原文出处：http://www.codeguru.com/forum/showthread.php?s=&threadid=247020