Creating a new C++ subvector?

问题:

Say I have a vector with values [1,2,3,4,5,6,7,8,9,10]. I want to create a new vector that refers to, for example, [5,6,7,8]. I imagine this is just a matter of creating a vector with pointers or do I have to push_back all the intermediary values I need?

回答1:

One of std::vector's constructor accepts a range:

std::vector<int> v;

// Populate v.
for (int i = 1; i <= 10; i++) v.push_back(i);   

// Construct v1 from subrange in v.
std::vector<int> v1(v.begin() + 4, v.end() - 2);

回答2:

This is fairly easy to do with std::valarray instead of a vector:

#include <valarray>
#include <iostream>
#include <iterator>
#include <algorithm>

int main() {
  const std::valarray<int> arr={0,1,2,3,4,5,6,7,8,9,10};

  const std::valarray<int>& slice = arr[std::slice(5, // start pos
                                                   4, // size
                                                   1  // stride
                                                  )];

}

Which takes a "slice" of the valarray, more generically than a vector.

For a vector you can do it with the constructor that takes two iterators though:

const std::vector<int> arr={0,1,2,3,4,5,6,7,8,9,10};
std::vector<int> slice(arr.begin()+5, arr.begin()+9);

回答3:

You don't have to use push_back if you don't want to, you can use std::copy:

std::vector<int> subvector;
copy ( v1.begin() + 4, v1.begin() + 8, std::back_inserter(subvector) );

回答4:

I would do the following:

#include <vector>
#include <iostream>

using namespace std;

void printvec(vector<int>& v){
        for(int i = 0;i < v.size();i++){
                cout << v[i] << " ";
        }
        cout << endl;
}

int main(){
        vector<int> v;

        for(int i = 1;i <= 10;i++) v.push_back(i);
        printvec(v);

        vector<int> v2(v.begin()+4, v.end()-2);
        printvec(v2);
        return 0;
}

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