How Can I Efficiently Append One Vector to Another in C ?

Appending Vectors Effortlessly

In the world of vector manipulation, there often arises the need to append one vector to the end of another. While iterating through the elements and making individual insertions might seem like the obvious approach, we're here to offer a more efficient and elegant solution.

Consider the following code snippet:

vector<int> a;
vector<int> b;

Assuming both vectors have around 30 elements, how can we add the contents of vector b to the end of vector a?

The brute-force method would involve using vector::push_back() to add each element of b to a. However, this approach can be tedious and computationally inefficient.

Instead, we introduce the more efficient method:

a.insert(a.end(), b.begin(), b.end());

Alternatively, for C 11 and above, consider this variant:

a.insert(std::end(a), std::begin(b), std::end(b));

These methods leverage the std::insert() function, which takes three arguments: an iterator to the insertion point, an iterator to the beginning of the source range, and an iterator to the end of the source range. By providing the appropriate iterators, we can seamlessly append the contents of vector b to vector a.

The second variant of the code snippet employs generic iterators, making it applicable to an array b as well. However, this approach requires C 11 or later.

For user-defined types, we can utilize Argument-Dependent Lookup (ADL) to simplify the code further:

using std::begin, std::end;
a.insert(end(a), begin(b), end(b));

With these elegant solutions, appending vectors becomes a effortless task, significantly enhancing the efficiency and maintainability of your code.

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