Write-Only pointer type

Question

I'm writing software for an embedded system.

We are using pointers to access registers of an FPGA device.
Some of the registers are read-only, while others are write-only.

The write-only registers will produce undefined values when read.

I want to define a pointer type that will allow the compiler to detect when reading values from a write-only registers (a.k.a. dereferencing).

Can a write-only pointer be created using only C language syntax?
(We are developing first prototype using C, but moving to C++ on 2nd generation.)

How can an efficient write-only pointer be created in C++? (Remember, this is not tracking items in dynamic memory, but accessing hardware addresses.)

This code is used on an embedded system where safety and quality are highest concerns.

Answer 1

I'd probably write a tiny wrapper class for each:

template <class T> class read_only {     T volatile *addr; public:     read_only(int address) : addr((T *)address) {}     operator T() volatile const { return *addr; } };  template <class T> class write_only {      T volatile *addr; public:     write_only(int address) : addr ((T *)address) {}      // chaining not allowed since it's write only.     void operator=(T const &t) volatile { *addr = t; }  }; 

At least assuming your system has a reasonable compiler, I'd expect both of these to be optimized so the generated code was indistinguishable from using a raw pointer. Usage:

read_only<unsigned char> x(0x1234); write_only<unsigned char> y(0x1235);  y = x + 1;         // No problem  x = y;             // won't compile