是否可以在 C++ 中将任意指针作为输入参数？

Question

我想创建一个类来管理 Cortex-M3 设备的位带功能。对于那些不知道的人：处理器将特定区域内的每一位映射到一个完整的单词。这允许对特定位进行原子集操作。该类本身适用于 std::uintptr_t。对于构造函数，我想允许一个任意指针，因为我不在乎它指向什么。它可能是设备头中定义的一些结构。

我当前的实现为构造函数提供：

Bitband(uintptr_t address, uint32_t bitNumber);
Bitband(void * ptr, uint32_t bitNumber);

我的应用程序这样调用构造函数：

Bitband foo(reinterpret_cast<uintptr_t>(&gpioPort->IDR), pin);

如果我遗漏他 reinterpret_cast，我将无法获得“uintptr_t”和“void *”的已知转换。 有没有一种干净的方法可以摆脱每次调用的 reinterpret_cast 并将任意指针作为构造函数的参数？

编辑：这是我当前的 Bitband 类代码以及我用于打开或关闭 LED 的用途：

bitband.hpp

#pragma once

#include <stdint.h>

class Bitband
{
public:
  Bitband(uintptr_t address, uint32_t bitNumber);
  Bitband(void * address, uint32_t bitNumber);

  inline void Set(bool val) const
  {
    uint32_t * const pData = reinterpret_cast<uint32_t *>(this->bbAddress);
    *pData = val;
  }

  inline bool Get() const 
  {
    uint32_t * const pData = reinterpret_cast<uint32_t *>(this->bbAddress);
    return *pData;
  }
private:
  static uintptr_t GetBitBandAddress(uintptr_t address, uint32_t bit);
  static bool IsSramAddress(uintptr_t address);
  static bool IsPeripheralAddress(uintptr_t address);

  uintptr_t const bbAddress;

/* Constants for bit band calculation for SRAM */
  static uintptr_t const sramStartAddress = 0x20000000;
  static uintptr_t const sramEndAddress   = 0x200FFFFF;
  static uintptr_t const sramBbBaseAddress = 0x22000000;

/* Constants for bit band calculation for Peripherals */
  static uintptr_t const peripheralsStartAddress = 0x40000000;
  static uintptr_t const peripheralsEndAddress   = 0x400FFFFF;
  static uintptr_t const peripheralsBbBaseAddress = 0x42000000;
};

bitband.cpp

#include "bitband.hpp"
#include <cassert>

Bitband::Bitband(uintptr_t address, uint32_t bitNumber) :
  bbAddress(GetBitBandAddress(address, bitNumber)) {}

Bitband::Bitband(void * address, uint32_t bitNumber) :
  bbAddress(GetBitBandAddress(reinterpret_cast<uintptr_t>(address), bitNumber)) {}

uintptr_t Bitband::GetBitBandAddress(uintptr_t const address,
                                      uint32_t const bitNumber)
{
  uintptr_t bbBase;
  uintptr_t regionStartAddress;

  assert(Bitband::IsPeripheralAddress(address)
          || Bitband::IsSramAddress(address));

  /* Set the parameters depending on wether we are in peripherals region or sram
    region. */
  if(Bitband::IsSramAddress(address))
  {
    bbBase = Bitband::sramBbBaseAddress;
    regionStartAddress = Bitband::sramStartAddress;
  }
  else if(Bitband::IsPeripheralAddress(address))
  {
    bbBase = Bitband::peripheralsBbBaseAddress;
    regionStartAddress = Bitband::peripheralsStartAddress;
  }
  else
  {
    /* Invalid parameter */
    __breakpoint(0);
  }

  uintptr_t byteOffset = address - regionStartAddress;
  auto bitWordOffset = (byteOffset * 32) + (bitNumber * sizeof(uint32_t));
  auto bitWordAddr = bbBase + bitWordOffset;

  return bitWordAddr;
}

bool Bitband::IsSramAddress(uintptr_t address)
{
  return (address >= Bitband::sramStartAddress)
            && (address <= Bitband::sramEndAddress);
}

bool Bitband::IsPeripheralAddress(uintptr_t address)
{
  return (address >= Bitband::peripheralsStartAddress)
            && (address <= Bitband::peripheralsEndAddress);
}

它被我的班级领导使用（用于测试我只是打开/关闭一些 LED）

led.hpp

#pragma once

#include <stdint.h>
#include "stm32l1xx.h"                  // Keil::Device:Startup
#include "bitband.hpp"

class Led
{
public:
  Led(GPIO_TypeDef * const ledPort, uint16_t ledPin);
  inline void Set(bool newState) { this->ledOutputBitBand.Set(!newState); }
private:
  Bitband ledOutputBitBand;
};

led.cpp

#include <led.hpp>
#include <cassert>

Led::Led(GPIO_TypeDef * const port, uint16_t const pin) :
    ledOutputBitBand(reinterpret_cast<uintptr_t>(&port->ODR), pin)
{
  assert(pin < 16);

  /* Set port mode to push pull */
  port->MODER |= 1 << ( 2 * pin);
}

在主应用程序中使用

Led greenLed(GPIOD, 0);
greenLed.Set(true);

如果我遗漏了 reinterpret_cast，我会收到以下消息：

Src/led.cpp(5): error: no matching constructor for initialization of 'Bitband'
    ledOutputBitBand(&port->ODR, pin)
    ^                ~~~~~~~~~~~~~~~

./Inc/bitband.hpp(9): note: candidate constructor not viable: no known conversion from 'volatile uint16_t *' (aka 'volatile unsigned short *') to 'uintptr_t' (aka 'unsigned int') for 1st argument; remove &
  Bitband(uintptr_t address, uint32_t bitNumber);
  ^

./Inc/bitband.hpp(10): note: candidate constructor not viable: no known conversion from 'volatile uint16_t *' (aka 'volatile unsigned short *') to 'void *' for 1st argument
  Bitband(void * address, uint32_t bitNumber);
  ^

./Inc/bitband.hpp(6): note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 2 were provided
class Bitband
      ^

./Inc/bitband.hpp(6): note: candidate constructor (the implicit move constructor) not viable: requires 1 argument, but 2 were provided
1 error generated.

所以我想如果我想在另一个上下文中使用类 Bitband，我必须再次使用 reinterpret_cast？

Answer 1

鉴于您提供的要求，是干净的方法。

我真的不明白你打算调用哪个构造函数（你没有明确你的目标），但不管怎样，reinterpret_cast 似乎最接近合理。

为了提醒您应该重新审视您的设计，并想出一个一开始就不需要这种转换的设计，它很冗长。因为我们不再生活在 1970 年代。 :)

但是，如果您坚持使用旧样式，则可以改用 C 样式转换：

Bitband foo((void*)&gpioPort->IDR, pin);

我恳求你不要这样做。