nuttx/libs/libxx/README.txt

libs/libxx/README.txt
^^^^^^^^^^^^^^^^^^^^^

This directory contains three C++ library:

 - A fragmentary C++ library that will allow to build only the simplest of
   C++ applications. In the deeply embedded world, that is probably all
   that is necessary.

   At present, only the following are supported here:

     - void *operator new(std::size_t nbytes);
     - void operator delete(void* ptr);
     - void operator delete[](void *ptr);
     - void __cxa_pure_virtual(void);
     - int __aeabi_atexit(void* object, void (*destroyer)(void*),
                          void *dso_handle);
     - int __cxa_atexit(__cxa_exitfunc_t func, FAR void *arg,
                        FAR void *dso_handle);

   This implementation is selected when neither of the following
   two options are enabled.

 - LLVM "libc++" C++ library (http://libcxx.llvm.org/)
   This implementation is selected with CONFIG_LIBCXX=y.

 - uClibc++ C++ library (http://cxx.uclibc.org/)
   This implementation is selected with CONFIG_UCLIBCXX=y.

operator new
------------

  This operator should take a type of size_t.  But size_t has an unknown underlying
  type.  In the nuttx sys/types.h header file, size_t is typed as uint32_t
  (which is determined by architecture-specific logic).  But the C++
  compiler may believe that size_t is of a different type resulting in
  compilation errors in the operator.  Using the underlying integer type
  instead of size_t seems to resolve the compilation issues. Need to
  REVISIT this.

  Once some C++ compilers, this will cause an error:

    Problem:     "'operator new' takes size_t ('...') as first parameter"
    Workaround:  Add -fpermissive to the compilation flags