任何内置函数来测试4是否在[1,2,3,4]（向量）中

In Ruby I can do:

在Ruby中,我可以做到:

 [1,2,3,4].include?(4) #=>True

In Haskell I can do :

在Haskell我能做到:

4 `elem`   [1,2,3,4]   #=> True

What should I do in C++?

我该怎么做C ++?

5 个解决方案

#1

There isn't a built-in function doing exactly that. There is std::find which comes close, but since it doesn't return a bool it is a bit more awkward to use.

没有内置函数正是这样做的。有一个std :: find接近,但由于它没有返回bool,使用起来有点尴尬。

You could always roll your own, to get syntax similar to JIa3ep's suggestion, but without using count (which always traverses the entire sequence):

您可以随时滚动自己,获得类似于JIa3ep建议的语法,但不使用count(总是遍历整个序列):

template <typename iter_t>
bool contains(iter_t first, iter_t last, typename iter_t::value_type val){
    return find(first, last, val) != last;
}

Then you can simply do this to use it:

然后你可以简单地这样做来使用它:

std::vector<int> x;

if (contains(x.begin(), x.end(), 4)) {...}

#2

Here an example using find:

这是一个使用find的例子:

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

int main() {
        std::vector<int> Num(4);
        //insert values
        Num[0]=1;
        Num[1]=2;
        Num[2]=3;
        Num[3]=4;
        std::vector<int>::iterator p = find(Num.begin(), Num.end(), 4);
        if (p == Num.end())
           std::cout  << "Could not find 4 in the vector"  << std::endl;
        else
           std::cout  << "Have found 4 in the vector"  << std::endl;
        return 0;
}

#3

If the vector is ordered, you can also use std::binary_search.

如果向量是有序的,您也可以使用std :: binary_search。

std::binary_search(vec.begin(), vec.end(), 4)  // Returns true or false

#4

To get similar syntax as in OP's question:

要获得与OP的问题类似的语法:

std::vector<int> x;

if ( count( x.begin(), x.end(), VAL_TO_FIND ) ) {
 // found
} else {
 // not found 
}

#5

You could use std::set This has a find() method.

你可以使用std :: set这有一个find()方法。

#1