C++11 风格的回调？
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C++11 styled callbacks?
提问by Klaim
I have a void function inside of a class. In old C++ i'd make a function static taking the class name as a parameter and had my own class which took a static void function + a void* for me to easily call it.
我在一个类中有一个 void 函数。在旧的 C++ 中，我会创建一个静态函数，将类名作为参数，并拥有我自己的类，它采用静态 void 函数 + 一个 void* 以便我轻松调用它。
However that feels old school. It also isn't templated which feels like i could be doing more. What is a more modern way of creating callbacks to myclassVar.voidReturnVoidParamFunc
然而，这感觉很老派。它也不是模板化的，感觉我可以做更多。什么是创建对 myclassVar.voidReturnVoidParamFunc 的回调的更现代的方法
回答by Klaim
Use std::functionand lambdas (or std::bind())to store callables:
使用std::function和 lambdas（或std::bind()）来存储可调用对象：
#include <functional>
#include <iostream>
class Test
{
public:
void blah() { std::cout << "BLAH!" << std::endl; }
};
class Bim
{
public:
void operator()(){ std::cout << "BIM!" << std::endl; }
};
void boum() { std::cout << "BOUM!" << std::endl; }
int main()
{
// store the member function of an object:
Test test;
std::function< void() > callback = std::bind( &Test::blah, test );
callback();
// store a callable object (by copy)
callback = Bim{};
callback();
// store the address of a static function
callback = &boum;
callback();
// store a copy of a lambda (that is a callable object)
callback = [&]{ test.blah(); }; // often clearer -and not more expensive- than std::bind()
callback();
}
Result:
结果：
BLAH!
BIM!
BOUM!
BLAH!
哎呀！
BIM！
砰！
哎呀！
Compiles and run: http://ideone.com/T6wVp
编译运行：http: //ideone.com/T6wVp
std::functioncan be used as any copyiable object, so feel free to store it somewhere as a callback, like in object's member. It also means that you can freely put it in standard containers, like std::vector< std::function< void () > >.
std::function可以用作任何可复制的对象，所以可以随意将它作为回调存储在某个地方，比如在对象的成员中。这也意味着您可以自由地将其放入标准容器中，例如std::vector< std::function< void () > >.
Also note that equivalent boost::function and boost::bindhave been available for years.
另请注意，等效的boost::function 和 boost::bind已经存在多年。
回答by LeslieM
For an example of passing in parameters to a C++ 11 callback using Lambda's and a vector, see http://ideone.com/tcBCeOor below:
有关使用 Lambda 和向量将参数传递给 C++ 11 回调的示例，请参阅http://ideone.com/tcBCeO或以下内容：
class Test
{
public:
Test (int testType) : m_testType(testType) {};
void blah() { std::cout << "BLAH! " << m_testType << std::endl; }
void blahWithParmeter(std::string p) { std::cout << "BLAH1! Parameter=" << p << std::endl; }
void blahWithParmeter2(std::string p) { std::cout << "BLAH2! Parameter=" << p << std::endl; }
private:
int m_testType;
};
class Bim
{
public:
void operator()(){ std::cout << "BIM!" << std::endl; }
};
void boum() { std::cout << "BOUM!" << std::endl; }
int main()
{
// store the member function of an object:
Test test(7);
//std::function< void() > callback = std::bind( &Test::blah, test );
std::function< void() > callback = std::bind( &Test::blah, test );
callback();
// store a callable object (by copy)
callback = Bim{};
callback();
// store the address of a static function
callback = &boum;
callback();
// store a copy of a lambda (that is a callable object)
callback = [&]{ test.blah(); }; // might be clearer than calling std::bind()
callback();
// example of callback with parameter using a vector
typedef std::function<void(std::string&)> TstringCallback;
std::vector <TstringCallback> callbackListStringParms;
callbackListStringParms.push_back( [&] (const std::string& tag) { test.blahWithParmeter(tag); });
callbackListStringParms.push_back( [&] (const std::string& tag) { test.blahWithParmeter2(tag); });
std::string parm1 = "parm1";
std::string parm2 = "parm2";
int i = 0;
for (auto cb : callbackListStringParms )
{
++i;
if (i == 1)
cb(parm1);
else
cb(parm2);
}
}
