如何检查MFC CString是否为空？

Question

I want to check if a MFC CString is null or not. Is there a way to do this?

PS: I want to check if it is null not if it's empty.

CString m_strName;

Answer 1

A CString object is never NULL . Unlike a char* or wchar* , which can be NULL , the internal buffer of a CString object which is a pointer always points to a data. For a given CString object, you can only differentiate whether it is empty or not using CString::IsEmpty() .

For the same reason, the LPCTSTR cast operator never returns NULL .

Answer 2

Due to the internal layout of the CString class template ¹⁾ , the pointer stored cannot ever be NULL .

The CString class template has a single class member: m_pszData . This member not only contains the string data, but also additional information (like string length, reference count, buffer capacity, etc.; see CStringData ). This additional information is stored to the left of the stored pointer. Both parts (string data and character buffer) must be allocated in a single block of memory, as there is only one pointer to reference both. Since the string data always needs to be there, the m_pszData can never be NULL .

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¹⁾ CString is a typedef for a particular CStringT template instantiation. The CStringT itself is derived from the CSimpleStringT class template.