Re: Autoconf 2.69 AC_PROG_CXX accepts plain C compilers

[Eric Blake]

On 02/05/2014 02:36 PM, Peter De Wachter wrote:
> On 05-02-14 21:40, Eric Blake wrote:
>> Actually, in gcc's case, your proposed program is now a syntax error:
>>
>> $ gcc -o foo foo.c
>> foo.c: In function ‘main’:
>> foo.c:1:21: error: ‘new’ undeclared (first use in this function)
>>  int main() { (void) new int; return 0; }

> 
> That's because you named the file "foo.c".
> 
> $ gcc -o foo foo.cpp
> /tmp/ccVVxj3a.o: In function `main':

Oh - so the gcc frontend changes language syntax based on file
extension, but does NOT change the linker backend to match.  Then yes, I
agree that we have to force a linker error.

> 'delete new int' should work as well. But I don't think defining a class
> is sufficient. To catch GCC, you need something that will cause a link
> error. Something like this would work:
> 
> #include <string>
> int main() { std::string s; return 0; }

Too complex to be reliable.

> 
> But using the standard library is difficult if you want to support old
> compilers that don't have namespace support.

I think you've convinced me that going with 'delete new int' is the way
to go.  I'll wait another day or so before pushing, in case anyone else
has comments.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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