https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86598
Bug ID: 86598
Summary: Incorrect lexing of pp-numbers in C++11 due to
hexfloat extension
Product: gcc
Version: 9.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: zhonghao at pku dot org.cn
Target Milestone: ---
g++ support C99 hexadecimal literals as an extension in its C++ modes. This is
*almost* a conforming extension in C++98 mode, but it's far from being one in
C++11 mode. For instance, in C++98:
#define PREFIX(x) foo ## x
void f() {
int PREFIX(1p);
int PREFIX(2p) = PREFIX(1p+5);
}
g++ rejects the above code:
code2.cpp:1:19: error: pasting "foo" and "1p+5" does not give a valid
preprocessing token
#define PREFIX(x) foo ## x
^~~
code2.cpp:4:19: note: in expansion of macro 'PREFIX'
int PREFIX(2p) = PREFIX(1p+5);
^~~~~~
code2.cpp: In function 'void f()':
code2.cpp:1:19: error: 'foo' was not declared in this scope
#define PREFIX(x) foo ## x
^~~
code2.cpp:4:19: note: in expansion of macro 'PREFIX'
int PREFIX(2p) = PREFIX(1p+5);
^~~~~~
code2.cpp:1:19: note: suggested alternative: 'foo2p'
#define PREFIX(x) foo ## x
^~~
code2.c.cpp:4:19: note: in expansion of macro 'PREFIX'
int PREFIX(2p) = PREFIX(1p+5);
^~~~~~
In the rules of C++, "1p+5" is three tokens, not one.
In C++11, this goes wrong in much less contrived situations:
Units<Amp> operator"" _amp(unsigned long long d);
int k = 4_amp+1; // incorrect error: no literal operator "" _amp+1
BTW, clang++ accepts the above code.
