https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108965
Bug ID: 108965
Summary: g++: unable to parse c11 _Generics
Product: gcc
Version: 11.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: chrisfriedt at gmail dot com
Target Milestone: ---
G++ version 11.3.0 fails to parse the C11 _Generic keyword. I would suspect
that earlier versions also fail to do this and likely also that later versions
fail as well.
gcc --version
gcc (Ubuntu 11.3.0-1ubuntu1~22.04) 11.3.0
Copyright (C) 2021 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
It's not clear to me if any part of the ISO C++ standard requires a C++
compiler to parse C11 _Generic, but it certainly can make life less pleasant,
as the equivalent C++ code can sometimes rely on static inline constexpr
templates which are apparently "not cool" until C++14. This particularly
affects people who are using somewhat older C++ toolchains that do not yet
support C++14.
LLVM has no problem, OTOH.
Sample taken from https://en.cppreference.com/w/c/language/generic
```
#include <stdio.h>
#include <math.h>
// Possible implementation of the tgmath.h macro cbrt
#define cbrt(X) _Generic((X), \
long double: cbrtl, \
default: cbrt, \
float: cbrtf \
)(X)
int main(void)
{
double x = 8.0;
const float y = 3.375;
printf("cbrt(8.0) = %f\n", cbrt(x)); // selects the default cbrt
printf("cbrtf(3.375) = %f\n", cbrt(y)); // converts const float to float,
// then selects cbrtf
}
```
```
g++ -o /tmp/main /tmp/main.cpp
/tmp/main.cpp: In function ‘int main()’:
/tmp/main.cpp:6:15: error: expected primary-expression before ‘long’
6 | long double: cbrtl, \
| ^~~~
/tmp/main.cpp:15:32: note: in expansion of macro ‘cbrt’
15 | printf("cbrt(8.0) = %f\n", cbrt(x)); // selects the default cbrt
| ^~~~
/tmp/main.cpp:7:19: error: expected primary-expression before ‘default’
7 | default: cbrt, \
| ^~~~~~~
/tmp/main.cpp:15:32: note: in expansion of macro ‘cbrt’
15 | printf("cbrt(8.0) = %f\n", cbrt(x)); // selects the default cbrt
| ^~~~
/tmp/main.cpp:8:21: error: expected primary-expression before ‘float’
8 | float: cbrtf \
| ^~~~~
/tmp/main.cpp:15:32: note: in expansion of macro ‘cbrt’
15 | printf("cbrt(8.0) = %f\n", cbrt(x)); // selects the default cbrt
| ^~~~
/tmp/main.cpp:5:17: error: ‘_Generic’ was not declared in this scope
5 | #define cbrt(X) _Generic((X), \
| ^~~~~~~~
/tmp/main.cpp:15:32: note: in expansion of macro ‘cbrt’
15 | printf("cbrt(8.0) = %f\n", cbrt(x)); // selects the default cbrt
| ^~~~
/tmp/main.cpp:6:15: error: expected primary-expression before ‘long’
6 | long double: cbrtl, \
| ^~~~
/tmp/main.cpp:16:35: note: in expansion of macro ‘cbrt’
16 | printf("cbrtf(3.375) = %f\n", cbrt(y)); // converts const float to
float,
| ^~~~
/tmp/main.cpp:7:19: error: expected primary-expression before ‘default’
7 | default: cbrt, \
| ^~~~~~~
/tmp/main.cpp:16:35: note: in expansion of macro ‘cbrt’
16 | printf("cbrtf(3.375) = %f\n", cbrt(y)); // converts const float to
float,
| ^~~~
/tmp/main.cpp:8:21: error: expected primary-expression before ‘float’
8 | float: cbrtf \
| ^~~~~
/tmp/main.cpp:16:35: note: in expansion of macro ‘cbrt’
16 | printf("cbrtf(3.375) = %f\n", cbrt(y)); // converts const float to
float,
| ^~~~
```
