Clang is behaving correctly here (as does GCC). You can't both stringize a token and concatenate in one step. Instead, use:

#define TESTL2(x) L##x
#define TESTL(x) TESTL2(#x)
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

Clang is behaving correctly here (as does GCC). You can't both stringize a
token and concatenate in one step. Instead, use:

#define TESTL2(x) L##x
#define TESTL(x) TESTL2(#x)
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

It also works with:

#define TESTL(x) L###x
const wchar_t* a = L"Hello World";
const wchar_t* b = TESTL(Hello World);

I wasn't sure of the desired behaviour of "L#x" in clang (or that GCC doesn't allow for it either), I ran into it while trying to analyze some Microsoft example code while working on a Visual Studio plugin for the clang analyzer. Is this something that should be added to the clang Microsoft extensions?

IMO we should consider lexing this as a single wide string literal in -fms-compatibility mode. There appear to be lots of Windows applications using this idiom to form wide string literals from macro arguments.

Fixed in revision 224228