Is there widely-available wide-character variant of `__FILE__`?

Question

One may generally use __LINE__ and __FILE__ in C++ programs, with many toolchains, including GCC.

__LINE__ under GCC evaluates

Answer 1

Use:

WIDE(MEXPAND(__FILE__))

and

WIDE(STRINGIFY(__LINE__))

or replace __LINE__ with anything that needs to be stringified, and replace __FILE__ with any macro string literal you want to widen.

Using the following definitions:

#define STRINGIFY2(m) #m
#define MEXPAND(m) m
#define STRINGIFY(m) STRINGIFY2(m)
#define WIDE(m) L ## m

Example usage:

#define AssertBreakMethod DebugBreak

#define AssertBreakForce(expr) \
  do \
  { \
    if (!(expr)) \
    { \
      OutputDebugStringW(WIDE(MEXPAND(__FILE__)) \
          WIDE("(") WIDE(STRINGIFY(__LINE__)) \
          WIDE("): Assertion failed: ") \
          WIDE(#expr) WIDE("\n")); \
      AssertBreakMethod(); \
    } \
  } \
  while (0)

Note that the whole parameter to OutputDebugString is assembled statically at compile time into a single string literal.

The trick with stringification of a macro is passing it through another macro. When __FILE__ is passed to MEXPAND it is expanded at that time. MEXPAND returns its argument which is now a string. It is then legal to put the leading L there to make it wide.

STRINGIFY does the same trick, it passes its argument through STRINGIFY2 which expands the argument to the line number (which looks like an integer at that point) then STRINGIFY2 puts the # symbol before it, stringifying the integer.