std :: function<>和标准函数指针？ [英] Difference between std::function<> and a standard function pointer?
问题描述
std :: function<>和标准函数指针之间的区别是什么？
Whats the difference between std::function<> and a standard function pointer?
：
typedef std::function<int(int)> FUNCTION;
typedef int (*fn)(int);
它们是否是同样的东西？
Are they effectively the same thing?
推荐答案
函数指针是在C ++中定义的实际函数的地址。 std :: function 是一个包装器，可以容纳任何类型的可调用对象（看起来像函数的对象）。
A function pointer is the address of an actual function defined in C++. An std::function is a wrapper that can hold any type of callable object (objects that look like functions).
struct FooFunctor
{
void operator()(int i) {
std::cout << i;
}
};
// Since `FooFunctor` defines `operator()`, it can be used as a function
FooFunctor func;
std::function<void (int)> f(func);
这里， std :: function 抽象出什么样的可调用对象，你正在处理—你不知道它是 FooFunctor ，你只是知道它返回 void 并有一个 int 参数。
Here, std::function allows you to abstract away exactly what kind of callable object it is you are dealing with — you don't know it's FooFunctor, you just know that it returns void and has one int parameter.
一个真实的例子，这个抽象是有用的是当你使用C ++与另一种脚本语言。您可能希望设计一个界面，以通用方式处理C ++中定义的函数以及脚本语言中定义的函数。
A real-world example where this abstraction is useful is when you are using C++ together with another scripting language. You might want to design an interface that can deal with both functions defined in C++, as well as functions defined in the scripting language, in a generic way.
修改：
std :: function 还可以找到 std :: bind 。这两个是一起使用时非常强大的工具。
Alongside std::function, you will also find std::bind. These two are very powerful tools when used together.
void func(int a, int b) {
// Do something important
}
// Consider the case when you want one of the parameters of `func` to be fixed
// You can used `std::bind` to set a fixed value for a parameter; `bind` will
// return a function-like object that you can place inside of `std::function`.
std::function<void (int)> f = std::bind(func, _1, 5);
在该示例中， bind 接受第一个参数 _1 ，并将其作为 a c传递给 func / code>参数，并将 b 设置为常量 5 。
In that example, the function object returned by bind takes the first parameter, _1, and passes it to func as the a parameter, and sets b to be the constant 5.
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