Get a slice or a sub-vector from a vector in C++

In this quick article, we’ll explore to get a slice or a sub-vector from a given vector in C++.

1. Using Range Constructor

The idea is to get input iterators to the starting and ending position in the vector and pass them to the range constructor of the vector class to get a sub-vector.

#include <iostream>

#include <vector>

template<typename T>

void print(std::vector<T> const &v)

{

for (auto i: v) {

std::cout << i << ' ';

}

std::cout << std::endl;

}

template<typename T>

std::vector<T> slice(std::vector<T> const &v, int m, int n)

{

auto first = v.cbegin() + m;

auto last = v.cbegin() + n + 1;

std::vector<T> vec(first, last);

return vec;

}

int main()

{

// input vector

std::vector<int> v = { 1, 2, 3, 4, 2, 2, 4, 6, 5 };

// starting and ending index

int m = 4, n = 7;

std::vector<int> sub_vec = slice(v, m, n);

print(sub_vec);

return 0;

}

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Output:

2 2 4 6

2. Using `std::copy` function

We can also use the standard algorithm std::copy for copying part of a vector to another vector, as shown below:

template<typename T>

std::vector<T> slice(std::vector<T> &v, int m, int n)

{

std::vector<T> vec(n - m + 1);

std::copy(v.begin() + m, v.begin() + n + 1, vec.begin());

return vec;

}

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Before calling std::copy, make sure the destination vector has enough space to accommodate all elements. If this is not the case, prefer using std::back_insert iterator, which will call push_back() on the specified vector, as shown below:

template<typename T>

std::vector<T> slice(std::vector<T> &v, int m, int n)

{

std::vector<T> vec;

std::copy(v.begin() + m, v.begin() + n + 1, std::back_inserter(vec));

return vec;

}

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That’s all about getting a slice or a sub-vector from a vector in C++.

Get a slice or a sub-vector from a vector in C++

1. Using Range Constructor

2. Using std::copy function

2. Using `std::copy` function