Can we use POSIX C libraries in C ++?

Basically, you should be able to use any C API from C ++; the language includes functions to facilitate it, and most C library authors know that people want to do this and will take the appropriate steps. For system programming interfaces specified in POSIX, C ++ compatibility is an explicit design goal.

However, you may still run into problems. In my experience, the most common problems are:

• API headers The API often dumps hundreds of characters into the global namespace. Some of these symbols can conflict with symbols in the C ++ library, which can get you in trouble if you using namespace std
  
  (but you didn't, did you?)
• Macros are often used in API headers, including macro names that may conflict with symbols in the C ++ library; std::
  
  will not keep you there.
• Compiling your program in strict match mode (for example -std=c++11 -D_XOPEN_SOURCE=700
  
  ) can reveal errors in system headers. This is more likely to happen with C ++ than C.
• A small subset of POSIX APIs have abnormal control flow behavior that can interact poorly with C ++ exceptions and destructors, depending on how careful your C library developer has been to avoid the problem. setjmp
  
  and longjmp
  
  obviously concern here (someone made the C library implementing the tops of exception handling DWARF style?) but also fork
  
  , setcontext
  
  and friends pthread_cancel
  
  , pthread_cleanup_push
  
  and perhaps a few others I can not remember from the head. (I remember a giant, ultimately flimsy argument between Ulrich Drepper and the CCC C ++ guys back in 2004 or so of exactly how one pthread_cancel
  
  should behave in the presence of destructors.)

If you go outside of POSIX you may also have problems with:

• Headers that didn't bother to wrap all the declarations in a extern "C"
  
  block when compiled in C ++, which means all function names get malformed when they shouldn't, and the linking fails.
• Headers that didn't even bother sticking to the intersection of C and C ++. In the worst case, this can lead to crashes that do not appear until the program is started. The most common examples of this are:
  • Blithely using some C ++ keyword as the declared name (for example int template;
    
    )
  • Assuming that void *
    
    is an assignment that is compatible with other types of pointers (e.g. no need to emit a result malloc
    
    )
  • Assuming it struct foo;
    
    doesn't define a typedef-namefoo
    
    

Note that headers referenced by POSIX often contain system extensions that have not been as carefully thought out as the POSIX interfaces themselves.