模拟python的“输入"在C ++中 [英] Simulating python's "in" in C++

问题描述

我设法弄清了python中的确切语法(检查容器中是否存在值)，因此您可以只检查值是否在任何支持begin()/end()方法的容器中.

I managed figure out exact syntax like in python (checking if value is present in container), so you can just check if value is "in" any container that supports begin()/end() methods.

这是我的实现方式

#include <algorithm>
#include <iostream>
#include <vector>

template<class T>
struct specified {
    specified(T const& value) : value_(value) {}
    T value_;

    template<class Container>
    bool operator * (Container const& cont) {
        return (std::find(cont.begin(), cont.end(), value_) != cont.end());
    }

};

struct general {
    template<class T>
    friend specified<T> operator *(T const& rhs, general const&) {
        return specified<T>(rhs);
    }
};

#define in * general() *

int main() {
    std::vector<int> vec{1,2,3};
    std::cout << 1 in vec << std::endl;
    std::cout << 4 in vec << std::endl;
}

在Coliru上直播

我的问题是，它有什么陷阱吗?安全吗?

My question is, does it have any pitfalls? Is it safe?

支持字符串文字

推荐答案

对于字符串，它有一个小的解决方法.

It has a small workaround for strings.

在使用字符串文字时无法正常工作.

Doesn't work as expected with string literals.

std::vector<string> vec{"1","2","3"};
std::cout << "1" in vec << std::endl;
std::cout << "4" in vec << std::endl;

此代码会导致编译时错误.

This code results in compile-time error.

error: array used as initializer
  specified(T const& value) : value_(value) {}

C ++将字符串文字作为char[]，而不是将其作为string.因此，我们需要明确提及它.

C++ takes the string literals as char[] instead of taking it as string. So we need to explicitly mention it.

std::cout << string("1") in vec << std::endl;

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