通过引用传递向量并在基于范围的 for 循环中更改其值? [英] Passing a vector by reference and changing its values in a range-based for loop?

问题描述

我正在尝试通过执行类似于以下函数的操作来更改向量的值:

I'm trying to change the values of a vector by doing something similar to the following function:

vector<int> Question2_Part3(vector<int> &v){

    for(auto elem : v){
        elem *= 2;
        cout << elem << " ";
    }
    cout << "
" << endl;

    return v;
}

这可能吗?我知道在我的 for 循环中，改变的是 elem 的值.我可以在更改 v 中的值的同时获得相同的输出，并且仍然使用基于范围的 for 循环吗?

Is this possible? I know that in my for loop, it is the value of elem that is changing. Can I have the same output while also changing the values in v and still use a range-based for loop?

推荐答案

是的，可以，但请使用参考

Yes it is possible but use a reference

for (auto &elem : v) {
    elem *= 2;
    cout << elem << " ";
}

这也更有效，因为它避免了将每个向量元素复制到变量中.其实如果你不想改变你应该做的元素

This is also more efficient as it avoids copying each vector element to a variable. Actually if you didn't want to change the elements you should do

for (const auto &elem : v) {
    cout << elem << " ";
}

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