What\'s the Most Efficient Way to Concatenate Vectors in a Multithreaded Environment?

Efficient Vector Concatenation in Multithreaded Environments

In multithreaded programming, the need to merge results from multiple threads arises frequently. A common scenario involves concatenating vectors containing data. The goal of this article is to determine the most efficient approach for performing this operation.

Question: Best Way to Concatenate Vectors

Suppose we have three vectors:

• A


• B


• AB
We want to create a new vector AB that contains the contents of both A and B, in that order.


What is the most efficient way to achieve this?

Answer: Using Reserve and Insert

The most efficient way to concatenate two vectors is to use the reserve() and insert() methods. The following code demonstrates this approach:

<code class="cpp">AB.reserve( A.size() + B.size() ); // preallocate memory
AB.insert( AB.end(), A.begin(), A.end() );
AB.insert( AB.end(), B.begin(), B.end() );</code>

1. reserve(): Before any insertion operations, we reserve sufficient memory in AB to accommodate the combined size of A and B. This optimization prevents costly reallocations during concatenation.
2. insert(): We use insert() twice to append the elements of both A and B to AB. The end() iterators specify the insertion points at the end of AB.

This approach is efficient because it avoids copying the vector elements and only requires a single memory allocation.

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