在C ++中将函数作为参数传递 [英] Passing functions as arguments in C++

问题描述

我对C ++有点生疏，经过一年的python转换.自然，我想将python的懒惰翻译成C ++.

I'm a bit rusty in C++ and I'm switching after a year of python. Naturally I would like to translate the laziness coming from python to C++.

我刚发现rot13，我对此感到非常兴奋.我找到了3种方法来做，我想做一点性能测试. 我还想看看在适当位置修改字符串或创建新字符串是否有区别.所以我最终有6个功能.

I just discovered rot13 and I'm all excited about it. I found 3 ways of doing it and I wanted to do a little performance test. I wanted to see also if there is a difference in modifying the string in place or creating a new one. So I ended up having 6 functions.

在第一种方法中，我使用std :: map来映射字符，因此，我建立了一个初始化映射的类，在第二种方法中，我使用了三元运算符，第三种方法是使用了位移.

In the first method, I use a std::map to map the characters, thus I've built a class that initializes the map, in the second I use a ternary operator, and the third I use a bit shift.

现在函数原型看起来像这样

Now the functions prototypes look like this

// map dependent
void Rot13::convert_inplace(string& mystr){

string Rot13::convert(const string& mystr){

// ternary operator
void bitrot_inplace(string& mystr){

string bitrot(const string&  mystr){

// bit shift
void bitshiftrot_inplace(string& mystr){

string bitshiftrot(const string& mystr){

我想构造一个接受这些函数作为参数的函数，然后计算时间并打印结果

I wanted to construct a function that accept those functions as arguments to then calculate the time and print the results

所以我看了一下stackoverflow， 1 ， 2 ，我想出了这个

So I had a look at stackoverflow, 1, 2, and I came up with this

typedef void (*vfc)(string str);

void printtime_inplace(string title, vfc func){

我尝试了这种构造，但是这意味着我受到vfc返回类型(在我的情况下为void或string)的限制，并且受制于我需要传递类的指针的事实. 因此，我将必须做3个函数来容纳不同的函数，即用于类成员函数的函数，用于void返回类型的函数和用于字符串返回类型的函数.

I tried this construction yet this means I'm limited by the vfc return type which in my case is either void or string, and by the fact I need to pass the pointer of the class. Thus I will have to do 3 functions to accommodate the different functions, namely a function for the class member function, a function for the void return type and a function for the string return type.

所以我问自己，是否真的需要使用模板而不编写相同功能的3倍?我对模板真的不确定，但是我应该做3 typedefs并构造printtime函数来接受模板吗?此外，有没有办法告诉模板您将只接受这些类型(即我定义的类型)?

So I asked myself, is this the case where I really need to use templates to not write 3 times the same function? I'm really not confident with templates but should I do 3 typedefs and structure the printtime function to accept a template? Moreover is there a way to tell the template you will accept only these types (namely the one I defined)?

另一个问题，这可以说是一个好的设计吗?还是您会建议其他设计?另一种实现方式?

An other question, is this let's say a good design? or would you suggest an other design? An other implementation?

推荐答案

最简单的方法IMO是使用模板，而不是尝试编写具有具体类型的函数.

The easiest way, IMO, is to use a template instead of trying to write a function with a concrete type.

template<typename Function>
void printtime_inplace(string title, Function func)
{
    //...
    func(title);
    //...
}

现在，您可以使用功能"中的任何内容.基本上，您可以将其传递给常规函数，函子，lambda，std::function.编译器将为您标记出不同的实例，但是就您的代码而言，您正在调用同一函数.

This will now allow you to take anything that is a "function". You can pass it a regular function, a functor, a lambda, a std::function, basically, any callable. The compiler will stamp out different instantiations for you but as far as your code is concerned you are calling the same function.

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