[SOLVED] error: expected unqualified-id before ‘__extension__’ in Linux (Cent OS)

Issue

My code is below,

namespace A
{
     namespace B
     {
           unsigned int htonl(unsigned int address)
           {
                return 0;
           }
     }
}

Now I know that htonl is a library function in Linux. Even though I am defining it under namespaces it produces the mentioned error. How can I fix it without changing the function signature?

Solution

The problem here is that htonl, in Linux at least, is a (sometimes) macro that expands to __bswap32, which in turn is a rather long macro (which has __attribute__((extension)) as part of it). Macros do not "care" about namespaces.

If you REALLY want your own function that is called htonl (you probably do not, in general - call it something else), then you can do

#ifdef htonl
#undef htonl
#endif

The #ifdef is there to avoid undefining something that isn't a macro.

Or you could figure out which header file it is that produces htonl (<arpa/inet.h> in my Linux installation) and not include that in your code.

Answered By - Mats Petersson

Answer Checked By - Mary Flores (WPSolving Volunteer)