问题描述
我正在创建一个用于 Sketch 的 Arduino 库.它使用 Encoder Library，但是在编译时出现了一个钝错误:>
/var/folders/jy/f8dvlhcd4vdcvtl49bk8ytwc0000gn/T/builda847c0675e0bee2f5f05581e35ae65fe.tmp/sketch/MIDIEncoder.cpp:在构造函数中:: 'MIDIEncoderuint, 'MIDIEncoderuint', byteEncoderuintMIDIEncoder.cpp:8: 错误:没有匹配的函数调用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:注意:候选人是:在/var/folders/jy/f8dvlhcd4vdcvtl49bk8ytwc0000gn/T/builda847c0675e0bee2f5f05581e35ae65fe.tmp/sketch/MIDIEncoder.h:17:0 包含的文件中，来自/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: 注意:Encoder::Encoder(uint8_t, uint8_t)编码器(uint8_t pin1，uint8_t pin2){^/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:72:2: 注意:候选人需要 2 个参数，0 提供/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7:注意:constexpr Encoder::Encoder(const Encoder&)类编码器^/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7:注意:候选人需要 1 个参数，0 提供/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7:注意:constexpr Encoder::Encoder(Encoder&&)/Applications/Arduino.app/Contents/Java/hardware/teensy/avr/libraries/Encoder/Encoder.h:69:7:注意:候选人需要 1 个参数，0 提供没有匹配的函数调用 'Encoder::Encoder()'
从根本上说，我相信编译器告诉我它找不到 Encoder 库的构造函数 MIDIEncoder.cpp:8: error: no matching function for call to '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
/*MIDI编码器.h用于从旋转编码器创建相关 MIDI CC 消息的库.由 Paul Williamson 创建，2016 年 8 月 11 日.项目来源可在:http://github.com/squarefrog/teensy-midi-encoder-box发布到公共领域.*/#ifndef MIDIEncoder_h#define MIDIEncoder_h#include "Arduino.h"#include <Encoder.h>MIDI 编码器类{民众:MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber);字节通道；字节 ccNumber;字节读取()；私人的:无符号长 _lastTurnedTime;长_oldPosition;编码器_enc;};#万一MIDIEncoder.cpp
#include "MIDIEncoder.h"#include <Encoder.h>常量字节增量值 = 66;//增量值开始的常量const 字节减量值 = 2;//递减值开始的常量MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber){频道 = midiChannel;ccNumber = midiCCNumber;_enc = 编码器(pin1, pin2);_oldPosition = -999;_lastTurnedTime = 毫秒()；}字节 MIDIEncoder::read(){long newPosition = _enc.read();//如果位置没有改变，忽略.如果(新位置 == _oldPosition){返回0；}//如果位置不能被 4 整除，则忽略.如果(新位置％4！= 0){返回0；}unsigned long delta = millis() - _lastTurnedTime;字节偏移= 0;//应用粗加速如果 (delta 99 && delta 179 && delta _旧位置){返回增量值 + 偏移量；} 别的 {返回减量值 + 偏移量；}}下面有一些很好的答案.现在我知道要找什么了，我找到了 这个资源 这解释了我在哪里犯了错误.特别注意数字 3.
Encoder 没有默认构造函数，这里隐式调用
MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber)/*隐式构造函数调用*/{//...}您尝试将其称为构造函数体，但到那时为时已晚":) 我的意思是，_enc 必须在构造函数体执行时已经初始化，但是 _enc 不能默认初始化，所以编译器报错.
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)//为_enc调用合适的构造函数，不是默认的{//...}I am creating an Arduino library for use in a Sketch. It uses the Encoder Library, but when compiling I get an obtuse error:
Fundamentally, I believe the compiler is telling me it can't find a constructor for the Encoder library MIDIEncoder.cpp:8: error: no matching function for call to 'Encoder::Encoder()', but I'm stumped as to why. Below is the full source for my library.
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;
}
}
Some excellent answers below. Now that I know what to look for I found this resource which explains where I made my mistake. In particular look at number 3.
Encoder doesn't have a default constructor, and it is implicitly call here
MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber)
/*Implicit constructor call*/
{
//...
}
You tried to call it the the constructor body, but by then "it is too late" :) What I mean is, _enc has to be already initialized when the constructor body executes, but _enc can't be default initialized, so the compiler complains.
That's what the constructor initializer list is for:
MIDIEncoder::MIDIEncoder(uint8_t pin1, uint8_t pin2, byte midiChannel, byte midiCCNumber)
: _enc(pin1, pin2) //Calls appropriate constructor for _enc, not default
{
//...
}
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