c++ - Arduino 库中没有调用的匹配函数

Question

我正在创建一个用于 Sketch 的 Arduino 库。它使用 Encoder Library , 但在编译时我得到一个迟钝的错误:

/var/folders/jy/f8dvlhcd4vdcvtl49bk8ytwc0000gn/T/builda847c0675e0bee2f5f05581e35ae65fe.tmp/sketch/MIDIEncoder.cpp: In constructor 'MIDIEncoder::MIDIEncoder(uint8_t, uint8_t, byte, byte)': MIDIEncoder.cpp:8: error: no matching function for call to 'Encoder::Encoder()' MIDIEncoder::MIDIEncoder(uint8_t pinA, uint8_t pinB, byte midiChannel, byte midiCCNumber) ^ /var/folders/jy/f8dvlhcd4vdcvtl49bk8ytwc0000gn/T/builda847c0675e0bee2f5f05581e35ae65fe.tmp/sketch/MIDIEncoder.cpp:8:89: note: candidates are: In file included from /var/folders/jy/f8dvlhcd4vdcvtl49bk8ytwc0000gn/T/builda847c0675e0bee2f5f05581e35ae65fe.tmp/sketch/MIDIEncoder.h:17:0, from /var/folders/jy/f8dvlhcd4vdcvtl49bk8ytwc0000gn/T/builda847c0675e0bee2f5f05581e35ae65fe.tmp/sketch/MIDIEncoder.cpp:2: /Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:72:2: note: Encoder::Encoder(uint8_t, uint8_t) Encoder(uint8_t pin1, uint8_t pin2) { ^ /Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:72:2: note: candidate expects 2 arguments, 0 provided /Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7: note: constexpr Encoder::Encoder(const Encoder&) class Encoder ^ /Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7: note: candidate expects 1 argument, 0 provided /Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7: note: constexpr Encoder::Encoder(Encoder&&) /Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7: note: candidate expects 1 argument, 0 provided no matching function for call to 'Encoder::Encoder()'

从根本上说，我相信编译器告诉我它找不到编码器库的构造函数 MIDIEncoder.cpp:8: 错误:没有匹配的函数来调用 'Encoder::Encoder()'，但我不知道为什么。以下是我的图书馆的完整来源。

MIDIEncoder.h

/*
  MIDIEncoder.h
  A library for creating relative MIDI CC messages from a rotary encoder.

  Created by Paul Williamson, 11 August 2016.

  Project source available at:
  http://github.com/squarefrog/teensy-midi-encoder-box

  Released into the public domain.
*/

#ifndef MIDIEncoder_h
#define MIDIEncoder_h

#include "Arduino.h"
#include <Encoder.h>

class MIDIEncoder
{
  public:    
  MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber);
    byte channel;
    byte ccNumber;

    byte read();

  private:
    unsigned long _lastTurnedTime;
    long _oldPosition;
    Encoder _enc;
};

#endif

MIDIEncoder.cpp

#include "MIDIEncoder.h"
#include <Encoder.h>

const byte incrementValue = 66; // A constant for the start of increment values
const byte decrementValue = 2;  // A constant for the start of decrement values

MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber)
{
  channel = midiChannel;
  ccNumber = midiCCNumber;
  _enc = Encoder(pin1, pin2);
  _oldPosition = -999;
  _lastTurnedTime = millis();
}

byte MIDIEncoder::read()
{
  long newPosition = _enc.read();

  // If position hasn't changed, ignore.
  if (newPosition == _oldPosition) {
    return 0;
  }

  // If position is not divisible by 4, ignore.
  if (newPosition % 4 != 0) {
    return 0;
  }

  unsigned long delta = millis() - _lastTurnedTime;
  byte offset = 0;

  // Apply crude acceleration
  if (delta < 100) offset = 4;
  if (delta > 99 && delta < 180) offset = 2;
  if (delta > 179 && delta <= 250) offset = 1;

  _lastTurnedTime = millis();

  // Return MIDI CC value
  if (newPosition > _oldPosition) {
    return incrementValue + offset;
  } else {
    return decrementValue + offset;
  }
}

---

下面有一些很好的答案。现在我知道要寻找什么了，我找到了 this resource这解释了我在哪里犯了错误。特别要看数字 3。

Answer 1

Encoder 没有默认构造函数，在这里隐式调用

MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber) 
    /*Implicit constructor call*/ 
{ 
    //...
}

您试图将其称为构造函数主体，但到那时“为时已晚”:) 我的意思是，_enc 必须在构造函数主体执行时已经初始化，但是 _enc 不能默认初始化，所以编译器会报错。

这就是构造函数初始化列表的用途:

MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber)
    : _enc(pin1, pin2) //Calls appropriate constructor for _enc, not default
{
    //...
}