[英]C++ signal callback (like javascript)
我是C ++的新手,並且在學習新語言的同時嘗試移植一些JavaScript腳本。
我正在嘗試找到使用像javascript這樣的回調的解決方案,尤其是像js-signals庫這樣的回調
以下是javascript中的腳本。 可以將其轉換為C ++嗎? 怎么樣? 如果沒有,什么是最佳解決方案?
使用Javascript
var ns = {
_callback: null,
setUpdate: function(callback) {
ns._callback = callback;
},
update: function() {
// do some default things
ns._callback();
}
};
ns.setUpdate(function() {
console.log("I'm Changed"); // will be: std::cout << "I'm Changed\n";
});
C ++
namespace ns {
// ??
};
// ns::setUpdate(??);
您可以使用函數指針,如下所示:
#include <cstdio>
namespace ns {
// defines a type named Callback that is a pointer
// to a function that takes void and returns void
typedef void (*Callback)();
Callback _callback;
void setUpdate( Callback cb) {
_callback = cb;
}
void update() {
_callback();
}
}
void MyUpdate() {
printf("hello from callback\n");
}
int main(int argc, char* argv[]) {
ns::setUpdate(MyUpdate);
ns::update();
}
輸出:
你好從回調
另請參見: Typedef函數指針?
我不會使用這樣的namespace
。 一個class
可能更適合這樣的事情:
#include <iostream>
#include <functional>
class MyThing
{
public:
MyThing() {}
MyThing(const std::function<void()>& callback) : callback_(callback) {}
void setUpdate(const std::function<void()>& callback)
{
callback_ = callback;
}
void update()
{
std::cout << "Update called\n";
if (callback_) {
callback_();
}
}
private:
std::function<void()> callback_;
};
int main()
{
MyThing my_thing1; // callback_ is initially unset in this object
my_thing1.update(); // no callback is called
my_thing1.setUpdate([](){ std::cout << "I'm Changed 1\n"; });
my_thing1.update(); // calls the lambda set in the previous line
MyThing my_thing2([](){ std::cout << "I'm Changed 2\n"; });
my_thing2.update(); // calls the lambda in the prevous line
}
這將輸出
更新稱為
更新稱為
我變了1
更新稱為
我變了2
這是將javascript js信號庫移植到c ++的好方法:
#include <string>
#include <map>
#include <functional>
// You only need this Signal class
class Signal {
// store all callbacks to a string map
std::map<std::string, std::function<void()>> callbacks;
// check if callback already exists. optional
bool exists(std::string key) {
if (callbacks.find(key) == callbacks.end()) {return false;}
else {return true;}
}
public:
void add(std::string key, std::function<void()> cb) {
if (!exists(key)) {remove(key);}
callbacks.insert(std::pair<std::string, std::function<void()>>(key, cb));
}
void remove(std::string key) {
callbacks.erase(key);
}
void dispatch() {
for (std::map<std::string, std::function<void()>>::iterator it = callbacks.begin(); it != callbacks.end(); it++) {
callbacks[it->first]();
}
}
// this destroys the signal
void dispose() {
callbacks.clear();
}
};
int main() {
// create a signal
Signal* onFire = new Signal();
// add some callbacks
int a_variable = 10;
onFire->add("a_sound_is_heard", [&]() {
// some code when onFire.dispatch() happens
std::cout << "i can use this variable too :) " << a_variable << std::endl;
// you can also use the onFire variable
});
onFire->add("a_bullet_appears", [&]() {
// some code again
});
// remove some callbacks (add a silencer for your gun)
onFire->remove("a_sound_is_heard");
// whenever you want, execute the event
onFire->dispatch();
// don't forget to delete the signal from memory
onFire->dispose();
delete onFire;
return 0;
}
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