What does _T stands for in a CString

Question

What does the "T" represents in a string. For example _T("Hello").I have seen this in projects where unicode support is needed.What it actually tells the processor

Solution 1

_T stands for “text”. It will turn your literal into a Unicode wide character literal if and only if you are compiling your sources with Unicode support. See http://msdn.microsoft.com/en-us/library/c426s321.aspx.

Solution 2

It's actually used for projects where Unicode and ANSI support is required. It tells the compiler to compile the string literal as either Unicode or ANSI depending on the value of a precompiler define.

Why you would want to do this is another matter. If you want to support Unicode by itself then just write Unicode, in this case L"Hello". The _T() macro was added when you needed to support Windows NT and later (which support Unicode) and Windows 9x/ME (which do not). These days any code using these macros is obsolete, since all modern Windows versions are Unicode-based.

Solution 3

From MSDN:

Use the _T macro to code literal strings generically, so they compile as Unicode strings under Unicode or as ANSI strings (including MBCS) without Unicode

Solution 4

It stands for TEXT. You can peek the definition when using IDE tools:

#define _TEXT(x)    __T(x)

But I would like to memorize it as "Transformable", or "swi-T-ch":

L"Hello"  //change "Hello" string into UNICODE mode, in any case;

_T("Hello") //if defined UNICODE, change "Hello" into UNICODE; otherwise, keep it in ANSI.

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Comments

[Remy Lebeau]

Technically, _T() is only used with the C runtime library, for use with the _TCHAR data type. The Win32 equivalent is the TEXT() macro for use with the TCHAR data type. Both map to char or wchar_t depending on whether _UNICODE and UNICODE are defined during compiling, respectively. Both are usually defined/undefined together, so many people tend to interchange them and things usually work. But they are logically separate and should be treated accordingly. Use _TCHAR and _T() with C functions. Use TCHAR and TEXT() with the Win32 API.

[IInspectable]

@RemyLebeau: Now here's the tricky question: Which one to use with MFC/ATL's CString type? CString is implemented both in terms of the CRT as well as the Windows API.

[Remy Lebeau]

Per the documentation: "CString is based on the TCHAR data type.", so use TEXT().