Placement new for MCU register abstraction proposed by Meyers

Question

I just tried to use a placement new operator as suggested by Scott Meyers in "Effectice C++ in an Embedded Environment".

    DefaultMcuType::PortRegister* p = new(reinterpret_cast<void*>(0x05)) DefaultMcuType::PortRegister;

Then I get the follwoing errors:

register.cc: In function 'int main()':
register.cc:30:90: error: no matching function for call to 'operator     new(sizetype, void*)'
 DefaultMcuType::PortRegister* p = new(reinterpret_cast<void*>(0x05))  DefaultMcuType::PortRegister;
                                                                                        ^~~~~~~~~~~~
<built-in>: note: candidate: void* operator new(unsigned int)
<built-in>: note:   candidate expects 1 argument, 2 provided
<built-in>: note: candidate: void* operator new(unsigned int,  std::align_val_t)
<built-in>: note:   no known conversion for argument 2 from 'void*' to  'std::align_val_t'
register.cc:30:35: warning: unused variable 'p' [-Wunused-variable]
 DefaultMcuType::PortRegister* p = new(reinterpret_cast<void*>(0x05))    DefaultMcuType::PortRegister;
                               ^

I really can't figure out what I am doing wrong.

Answer 1

Placement new is an operator function. Your specific one should be defined as

void* operator new ( std::size_t count, void* ptr );

in the header file <new>.

Using #include <new> should resolve your problem.

For an example see here: https://godbolt.org/g/iKatox

More information about the new operators can be found here: http://en.cppreference.com/w/cpp/memory/new/operator_new

---

Update:

If you don't have access to placement new you might define it yourself. I used the VC++14 version as a template for this:

#include <stdlib.h> //for std::size_t
inline void* operator new(std::size_t size, void* ptr)
{
  (void)size;//unused
  return ptr;
}

inline void operator delete(void*, void*)
{
  return;
}

You can compare both versions generating the same assembly code: https://godbolt.org/g/6UjER9