Read the registry through the ATL library clegkey (simple and convenient)

Preface

It didn't work much before ATL library , Basically, you are calling the system API, Microsoft API Cumbersome and complicated and many pits , Don't read carefully MSDN Original English document , I'm afraid to use it , Especially some rare API, A search on the Internet turned out to be a large area , But few are right , ha-ha ！

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Now the ATL The library is in use , Read and write like a file 、 The registry 、 Containers 、 Strings and so on , similar STL In the container ,ATL There are also basically , Personal feeling ATL The string class in is easier to use than the standard library , Of course, there are more pits , I don't say much nonsense , This article talks about passing ATL In the library CRegKey Class to read the registry ：

Take a simple example ：

#include <windows.h>
#include <atlbase.h>

int main()
{
	CRegKey reg;
	if (ERROR_SUCCESS == reg.Open(HKEY_LOCAL_MACHINE, L"SOFTWARE\\WOW6432Node\\Microsoft\\Windows\\CurrentVersion", KEY_READ))
	{
		WCHAR data[100] = { 0 };
		ULONG size = 99;
		//size For input and output    And represents sizeof(TCHAR) The number of 
		reg.QueryStringValue(L"SM_ConfigureProgramsName", data, &size);
		printf("%S\n",data);
		reg.Close();
	}

	system("pause");
}

Registry corresponding value ：

 CRegistry Of Open The first parameter of the function can be filled in the following macro , The definition is as follows , Anyone who has used the registry can understand it in seconds ：

HKEY_CLASSES_ROOT      
HKEY_CURRENT_USER               
HKEY_LOCAL_MACHINE         
HKEY_USERS                      
HKEY_PERFORMANCE_DATA       
HKEY_PERFORMANCE_TEXT            
HKEY_PERFORMANCE_NLSTEXT          
HKEY_CURRENT_CONFIG              
KEY_DYN_DATA                     
HKEY_CURRENT_USER_LOCAL_SETTINGS 

The second parameter is the path

The third parameter is the required permission , You can mainly fill in the following values ：

KEY_READ
KEY_WRITE         
KEY_EXECUTE           
KEY_ALL_ACCESS         

Open After the call is successful , The following functions are also provided to query various types of values ：

QueryBinaryValue	Call this method to retrieve the binary data for a specified value name.
QueryDWORDValue	Call this method to retrieve the DWORD data for a specified value name.
QueryGUIDValue	Call this method to retrieve the GUID data for a specified value name.
QueryMultiStringValue	Call this method to retrieve the multistring data for a specified value name.
QueryQWORDValue	Call this method to retrieve the QWORD data for a specified value name.
QueryStringValue	Call this method to retrieve the string data for a specified value name.
QueryValue	Call this method to retrieve the data for the specified value field of m_hKey. Earlier versions of this method are no longer supported and are marked as ATL_DEPRECATED.

It's used here QueryStringValue, The description of this function is as follows ：

Call this method to retrieve the string data for a specified value name.

LONG QueryStringValue(
   LPCTSTR pszValueName,
   LPTSTR pszValue,
   ULONG* pnChars 
) throw( );

Parameters

pszValueName

Pointer to a null-terminated string containing the name of the value to query.

pszValue

Pointer to a buffer that receives the string data.

pnChars

The size, in TCHARs, of the buffer pointed to by pszValue. When the method returns, pnChars contains the size, in TCHARs, of the string retrieved, including a terminating null character.

Return Value

If the method succeeds, ERROR_SUCCESS is returned. If the method fails to read a value, it returns a nonzero error code defined in WINERROR.H. If the data referenced is not of type REG_SZ, ERROR_INVALID_DATA is returned. If the method returns ERROR_MORE_DATA, pnChars equals zero, not the required buffer size in bytes.

Put a special emphasis on , The third parameter is in,out, That is, input as buffer Size , When the function returns, it represents the length of the read string , The size here is not in bytes , But rather char or wchar_t Unit .