Supporting string concatenation in _Pragma

[Myriachan]

It's quite annoying that the C99/C++11 directive _Pragma does not allow you to concatenate strings.  For example, with GCC/clang #pragma message:

#define ASDF "meow"
// OK
#pragma message ASDF ASDF
// Ill-formed: _Pragma takes a string literal argument
_Pragma("message \"" ASDF "\"")

From reading the Standard, I think that the reason you can't concatenate strings in _Pragma is because string concatenation occurs at a later phase.  Despite this, it seems to me that string concatenation ought to be allowed in a _Pragma for programmers' sake.

By the way, I feel that #pragma message ought to be standardized by C and C++.  It's really simple to define it as outputting a diagnostic with the specified string in the matter of a failed static_assert, but without making the program ill-formed.  And it could be optional to output a diagnostic for it; just make it accepted by all compilers.

If not #pragma message, then add something like #warning and #message, with similar definition to #error.  (The concept of "warning" is not defined by the Standard, so #warning could also be ignored at QoI discretion like #message / #pragma message.)

Melissa

[David Krauss]

On 2015–07–25, at 8:55 AM, Myriachan <myri...@gmail.com> wrote:

It's quite annoying that the C99/C++11 directive _Pragma does not allow you to concatenate strings.  For example, with GCC/clang #pragma message:

The typical usage is that you use a STRINGIZE macro to generate the string at the last minute. (If the string is not a literal, anyway.) IIRC that’s what the examples in the standard do. This requires that you don’t have illegal tokens and you don’t care too much about whitespace formatting, but it’s good enough.