[cfe-dev] clang vs GCC error case: both ‘const’ and ‘constexpr’ cannot be used here

[Jordan Rose]

[dcl.constexpr]p9: A constexpr specifier used in an object declaration declares the object as const.

[dcl.type]p2: const can be combined with any type specifier except itself.

I could see how GCC could interpret that as meaning "constexpr replaces const", but I think Clang is doing the right thing by allowing both specifiers. The constexpr's "declaring the object as const" is a semantic property, not an implicit inclusion of the const /specifier/.

I'm still not a standardista, though, so someone might have another view (or another citation I missed).
Jordan


On Jul 23, 2012, at 1:34 AM, Stephen Kelly wrote:

> 
> Hi there,
> 
> clang compiles the following code, but GCC does not:
> 
> 
> 
> #include <iostream>
> 
> static constexpr const char Data[] = {
>  'D', 'A', 'T', 'A',
> };
> static constexpr const char *data_func() { return Data; }
> 
> int main(int argc, char **argv)
> {
> 
>  char c = 'T';
> 
>  switch(c)
>  {
>    case *data_func():
>      std::cout << "GOT A D" << std::endl;
>      break;
>    case *(data_func() + 2):
>      std::cout << "GOT A T" << std::endl;
>  }
> }
> 
> 
> 
> $ clang++ --version
> clang version 3.2 
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> 
> $ g++ -dumpversion
> 4.6.1
> 
> $ g++ main.cpp -std=c++0x
> main.cpp:163:48: error: both ‘const’ and ‘constexpr’ cannot be used here
> 
> 
> Which compiler is buggy?
> 
> Thanks,
> 
> Steve.
> 
> 
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