How to recreate a vector without unnecessary copies in c++?

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by lonzo , in category: General Help , 2 months ago

How to recreate a vector without unnecessary copies in c++?

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1 answer

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by adelia , 2 months ago

@lonzo 

To recreate a vector without unnecessary copies in C++, you can use constructs like move semantics and emplace functions. Here's an example on how to achieve this:

  1. Move Semantics: Instead of creating unnecessary copies, move semantics allow you to transfer the ownership of resources from one object to another.
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std::vector<int> originalVector = {1, 2, 3}; // Or any other vector

// Copy the original vector with move semantics
std::vector<int> newVector = std::move(originalVector);


In this example, std::move is used to transfer the contents of originalVector to newVector efficiently, without making unnecessary copies. After this operation, originalVector is in a valid but unspecified state.

  1. Emplace Functions: Instead of first creating an object and then copying it to the vector, emplace functions directly construct the object inside the vector, avoiding the need for intermediate copies.
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std::vector<std::pair<int, std::string>> vectorPairs;

// Instead of creating a temporary pair and then copying it to the vector,
// emplace a new pair directly into the vector
vectorPairs.emplace_back(1, "one");
vectorPairs.emplace_back(2, "two");


In this example, emplace_back constructs the std::pair directly inside the vectorPairs vector, avoiding copies.


By using move semantics and emplace functions, you can avoid unnecessary copies when recreating or populating vectors in C++.