Multi-line raw string literals as preprocessor macros arguments

Question

Can a multi-line raw string literal be an argument of a preprocessor macro?

#define IDENTITY(x) x

int main()
{
    IDENTITY(R"(
    )");
}

This code doesn't compile in both g++4.7.2 and VC++11 (Nov.CTP).
Is it a compiler (lexer) bug?

It seems to be either a lexer or a pre-processor problem, in GCC at least. If I add a pre-processor line-continuation (ending the line in a backslash) it compiles, but the string contain the line-continuation character. Tested with GCC 4.7.2. — Some programmer dude
– Some programmer dude, Commented Nov 30, 2012 at 17:25
For what it's worth, Clang 3.1 has no problem compiling your example. — bfroehle
– bfroehle, Commented Jan 17, 2013 at 17:26

SteveL · Accepted Answer · 2012-11-30 18:28:20Z

2

Multiple line macro invocations are legal - since you are using a raw string literal it should have compiled

There is a known GCC bug for this:

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52852

If you had been using regular (nonraw) strings it would have been illegal.

This should have compiled:

printf(R"HELLO
    WORLD\n");

But not this:

printf("HELLO
    WORLD\n");

This should be coded as

printf("HELLO\nWORLD\n");

if a new line is intended between HELLO and WORLD or as

printf("HELLO "
    "WORLD\n");

If no intervening new line was intended.

Do you want a new line in your literal? If so then couldn't you use

  IDENTITY("(\n)");

The C compiler documentation at

http://gcc.gnu.org/onlinedocs/cpp.pdf

States that in section 3.3 (Macro Arguments) that

"The invocation of the macro need not be 
restricted to a single logical line—it can cross 
as many lines in the source file as you wish."

edited Nov 30, 2012 at 18:28

SteveL

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answered Nov 30, 2012 at 17:26

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2 Comments

Angew is no longer proud of SO Over a year ago

Your first example doesn't compile because it's an ordinary string literal. The OP used a raw string literal, which can contain source-file newlines (see [lex.string], esp. para 4 & 5). I side with the OP that it's a compiler bug.

Brandon Ros Over a year ago

How can you do this in just C, not C++? error: use of undeclared identifier 'R'

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