如何在C++中使用非静态成员函数作为回调 [英] How to use non static member functions as callback in C++
问题描述
我正在用 C++ 为 ESP8266 编写一个小程序,但遇到了麻烦.我创建了一个处理 LED 的 Led 类表单.这个想法是该类应该处理一个闪烁功能.为此,我使用了一个名为 Ticker 的库.
I am writing a small program for ESP8266 in C++ and run into trouble. I've created a Led class form handling leds. The idea is that the class should handle a blink function. For this I use a library called Ticker.
Ticker 中的一个函数,attach_ms 需要一个回调,我无法让它与非静态成员函数一起工作.
A function in Ticker, attach_ms requires a callback and I cant get that to work with a non static member functions.
这是我的头文件:
#ifndef led_h
#define led_h
#include <Arduino.h>
#include <Ticker.h>
#include "debugutils.h"
#define tickLength 100
enum class LedState {
OFF,
ON,
SLOW_BLINK,
FAST_BLINK
};
class Led {
public:
Led(Ticker *tick, uint8_t ledPin, int slowBlinkTime, int fastBlinkTime);
void on();
void off();
void slowBlink( );
void fastBlink( );
private:
uint8_t pin;
int counter;
int slowNoBlinkTicks;
int fastNoBlinkTicks;
LedState state;
void ledOn();
void ledOff();
void ledInvert();
void clean();
void blink(int par);
void tickerCallbackLed();
};
#endif
这是我的代码文件:
#include "led.h"
void Led::ledOn() {
digitalWrite(pin, HIGH);
}
void Led::ledOff() {
digitalWrite(pin, LOW);
}
void Led::ledInvert() {
digitalWrite(pin, !digitalRead(pin));
}
void Led::clean() {
counter = 0;
}
void Led::blink(int par) {
if (counter > par) {
ledInvert();
counter = 0;
}
else {
counter++;
}
}
void Led::tickerCallbackLed() {
switch (state) {
case LedState::OFF : break;
case LedState::ON : break;
case LedState::SLOW_BLINK : blink(slowNoBlinkTicks); break;
case LedState::FAST_BLINK : blink (fastNoBlinkTicks); break;
default : break;
};
};
void Led::on() {
ledOn();
state = LedState::ON;
};
void Led::off(){
ledOff();
state = LedState::OFF;
};
void Led::slowBlink(){
clean();
ledInvert();
state = LedState::SLOW_BLINK;
};
void Led::fastBlink(){
clean();
ledInvert();
state = LedState::FAST_BLINK;
};
Led::Led(Ticker *tick, uint8_t ledPin, int slowBlinkTime, int fastBlinkTime) {
tick->attach_ms(tickLength, std::bind(&Led::tickerCallbackLed,this));
slowNoBlinkTicks = slowBlinkTime/tickLength;
fastNoBlinkTicks = fastBlinkTime/tickLength;
pinMode(ledPin,OUTPUT);
digitalWrite(ledPin,LOW);
pin = ledPin;
state = LedState::OFF;
counter = 0;
}
这一行给出了一个编译错误,我不知道如何修复它.已尝试遵循我在互联网上找到的所有建议".
This line gives a compile error and I dont know how to fix it. Have tried to follow all "advice" I have found on internet.
tick->attach_ms(tickLength, std::bind(&Led::tickerCallbackLed,this));
推荐答案
根据 这个版本的 Ticker.h
,Ticker::attach_ms()
被重载以接受 std::function
或 void (*)(TArg)
作为回调:
According to this version of Ticker.h
, Ticker::attach_ms()
is overloaded to accept either a std::function<void(void)>
or a void (*)(TArg)
as the callback:
typedef void (*callback_with_arg_t)(void*);
typedef std::function<void(void)> callback_function_t;
void attach_ms(uint32_t milliseconds, callback_function_t callback)
{
_callback_function = callback;
attach_ms(milliseconds, _static_callback, (void*)this);
}
template<typename TArg>
void attach_ms(uint32_t milliseconds, void (*callback)(TArg), TArg arg)
{
static_assert(sizeof(TArg) <= sizeof(uint32_t), "attach_ms() callback argument size must be <= 4 bytes");
uint32_t arg32 = (uint32_t)arg;
_attach_ms(milliseconds, true, reinterpret_cast<callback_with_arg_t>(callback), arg32);
}
在第一种情况下,您可以使用带有 std::function
的 lambda,您根本不需要 std::bind()
:
In the first case, you can use a lambda with std::function
, you don't need std::bind()
at all:
tick->attach_ms(tickLength, [this](){ this->tickerCallbackLed(); });
在第二种情况下,callback
接受一个传递给 Ticker::attach_ms()
的用户定义参数,因此您可以传递 this
作为该参数(正如您在上面看到的,这正是 Ticker::attach_ms()
的 std::function
版本在内部所做的):
In the second case, the callback
takes a user-defined argument that is passed to Ticker::attach_ms()
, so you can pass this
as that argument (which, as you can see above, is exactly what the std::function
version of Ticker::attach_ms()
does internally):
class Led {
...
private:
...
static void staticTickerCallbackLed(Led *pThis);
void tickerCallbackLed();
...
};
void Led::staticTickerCallbackLed(Led *pThis)
{
pThis->TickerCallbackLed();
}
...
tick->attach_ms(tickLength, &Led::staticTickerCallbackLed, this);
但是请注意,Ticker::attach_ms()
不允许具有 > 的回调参数.大小为 4 个字节,这意味着在为 64 位编译时,任何一种方法都不起作用,其中指针为 8 个字节!恕我直言,这似乎是内部 Ticker::_attach_ms()
方法实现中的一个错误,该方法将回调参数作为 uint32_t
而不是 uintptr_t代码>:
Do note, though, that Ticker::attach_ms()
does not allow a callback argument that is > 4 bytes in size, which means either approach will not work when compiling for 64-bit, where pointers are 8 bytes! IMHO, that seems like a bug in the implementation of the internal Ticker::_attach_ms()
method, which takes in a callback argument as uint32_t
instead of as uintptr_t
:
void _attach_ms(uint32_t milliseconds, bool repeat, callback_with_arg_t callback, uint32_t arg);
这篇关于如何在C++中使用非静态成员函数作为回调的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!