Does extern "C" affect compilation mode

[Jonathan Wakely]

On 19 February 2011 13:40, Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
> On 19 February 2011 09:41, Graham Bloice wrote:
>> I'm getting problems with g++ compiling some headers:
>>
>> #ifdef __cplusplus
>> extern "C" {
>> #endif
>>
>> typedef enum abc xyz;
>> enum abc {
>>  p1 = 0,
>>  p2,
>>  p3
>> };
>>
>> #ifdef __cplusplus
>> }
>> #endif
>>
>> This code compiles with the mbed cloud compiler, Keil RV and VS2010,
>> but not g++ 4.4.5.  The errors are:
>>
>> test.cpp:5: error: use of enum ‘abc’ without previous declaration
>> test.cpp:5: error: invalid type in declaration before ‘;’ token
>>
>> From a previous query I understand that the code isn't legal c++, but
>> is legal c, as demonstrated when I compile the code using the -x c
>> option.
>>
>> I'm guessing here, but do some compilers switch into a C compilation
>> mode when they hit an extern "C"?  I know extern "C" affects the
>> linkage but is it meant to affect compilation mode?
>
> G++ doesn't, and a conforming compiler shouldn't - but this is the
> wrong place to ask about "somt compilers".
>
> For a conforming compiler extern "C" only tells the C++ compiler to
> use different linkage for the enclosed functions.  It absolutely does
> not cause it to compile as C, as can be shown by the fact that C++
> features are allowed inside extern "C" blocks:
>
> #include <string>
> extern "C" void f() { throw std::runtime_error("I am C++"); }
>

Oops, I should have included <stdexcept>, I changed the example and
didn't correct the header.