C++ 如何在 Visual Studio 11 中将成员函数直接绑定到 std::function？
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How to directly bind a member function to an std::function in Visual Studio 11?
提问by danijar
I can easily bind member functions to a std::functionby wrapping them with a lambda expression with capture clause.
我可以很容易地将成员函数绑定到 a std::function，方法是用带有捕获子句的 lambda 表达式包装它们。
class Class
{
Class()
{
Register([=](int n){ Function(n); });
}
void Register(std::function<void(int)> Callback)
{
}
void Function(int Number)
{
}
};
But I want to bind them directly, something like the following.
但我想直接绑定它们，如下所示。
// ...
Register(&Class::Function);
// ...
I think according to the C++11 standard, this should be supported. However, in Visual Studio 11 I get these compiler errors.
我认为根据C++11标准，这应该是支持的。但是，在 Visual Studio 11 中，我收到了这些编译器错误。
error C2440: 'newline' : cannot convert from 'int' to 'Class *'
error C2647: '.*' : cannot dereference a 'void (__thiscall Class::* )(int)' on a 'int'
错误 C2440：“换行符”：无法从“int”转换为“Class *”
错误 C2647：“.*”：无法在“int”上取消引用“void (__thiscall Class::*)(int)”
回答by juanchopanza
I think according to the C++11 standard, this should be supported
我觉得按照C++11标准，这个应该是支持的
Not really, because a non-static member function has an implicit first parameter of type (cv-qualified) YourType*, so in this case it does not match void(int). Hence the need for std::bind:
并非如此，因为非静态成员函数具有类型为 (cv-qualified) 的隐式第一个参数YourType*，因此在这种情况下它不匹配void(int)。因此需要std::bind：
Register(std::bind(&Class::Function, PointerToSomeInstanceOfClass, _1));
For example
例如
Class c;
using namespace std::placeholders; // for _1, _2 etc.
c.Register(std::bind(&Class::Function, &c, _1));
EditYou mention that this is to be called with the same Classinstance. In that case, you can use a simple non-member function:
编辑你提到这是用同一个Class实例调用的。在这种情况下，您可以使用一个简单的非成员函数：
void foo(int n)
{
theClassInstance.Function(n);
}
then
然后
Class c;
c.Register(foo);
回答by Andy
According to Stephan T. Lavavej - "Avoid using bind(), ..., use lambdas". https://www.youtube.com/watch?v=zt7ThwVfap0&t=32m20s
根据 Stephan T. Lavavej - “避免使用 bind()，...，使用 lambdas”。 https://www.youtube.com/watch?v=zt7ThwVfap0&t=32m20s
In this case:
在这种情况下：
Class()
{
Register([this](int n){ Function(n); });
}
回答by Some programmer dude
回答by peterchen
In C++ 17, you can use:
在 C++ 17 中，您可以使用：
Register([=](auto && ...args){ return Function(args...); });
which is sweet especially if the argument list is longer long.
Of course the member function's argument list must then be compatible with the std::function's ones.
这是甜蜜的，尤其是如果参数列表更长。当然，成员函数的参数列表必须与 的参数列表兼容std::function。
回答by Richard
With std::functionand std::bind, you can treat different class member function the same.
使用std::functionand std::bind，您可以将不同的类成员函数视为相同。
#include <iostream>
#include <functional>
#include <vector>
using namespace std;
using namespace std::placeholders;
class Foo
{
public:
void foo(const string &msg)
{
cout << msg << '\n';
}
};
class Bar
{
public:
void bar(const string &msg, const string &suffix)
{
cout << msg << suffix << '\n';
}
};
int main(int argc, char **argv)
{
Foo foo;
Bar bar;
vector<function<void (const string &msg)>> collection;
collection.push_back(bind(&Foo::foo, &foo, _1));
collection.push_back(bind(&Bar::bar, &bar, _1, "bar"));
for (auto f : collection) {
f("foo");
}
return 0;
}
