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Re: error: template with C linkage
Marc Glisse <marc.glisse@inria.fr> writes:
> On Sun, 18 Sep 2011, Jeffrey Walton wrote:
>
>> On Sat, Sep 17, 2011 at 4:21 PM, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>>> On 17 September 2011 14:23, Jeffrey Walton wrote:
>>>> /usr//include/cryptopp/cryptlib.h:99: error: template with C linkage
>>> ...
>>>> I've tried adding '-x c++' to force c++ in the files.
>>>
>>> That's obviously not going to help.
>>>
>>> If the compiler complains about a template, it's not compiling C,
>>> because there's no such thing in C. ÂDitto for C linkage; everything
>>> in C has C linkage, so there's no concept of any other kind of
>>> language linkage, so no reason a C compiler would ever mention "C
>>> linkage". ÂSo the compiler was already treating the files as
>>> containing C++ (just apparently assuming that everything in a system
>>> directory gets an implicit extern "C" around it.)
>> OK, thanks. I'm not sure what the implications of "system compiler"
>> are, but OpenBSD's configuration did not like those files in
>> /usr/include.
>>
>> $ g++ -v
>> Reading specs from /usr/bin/../lib/gcc-lib/i386-unknown-openbsd4.9/4.2.1/specs
>> Target: i386-unknown-openbsd4.9
>> Configured with: OpenBSD/i386 system compiler
>> Thread model: posix
>> gcc version 4.2.1 20070719
>> $
>>
>> Do you have any ideas why a location would make a difference?
>
> Antique platforms have system headers that don't know about C++, so
> g++ implicitly adds extern "C" around them. And being a system header
> is a property that depends on the directory the file is in.
This approach is controlled on a target-by-target basis, by the way. If
OpenBSD's header files are C++ ready, gcc's OpenBSD target configuration
should be changed to define NO_IMPLICIT_EXTERN_C.
Ian