Difference between std::swap and std::vector::swap

in C++. But before discussing the difference, we must know about the std::swap and std::vector::swap in C++.

What is std::swap?

The utility function std::swap is defined in the C++ standard library's <algorithm> header. It allows swapping the values of two objects.

Syntax:

The syntax of std::swap is:

It takes two arguments; both reference objects of type T. It swaps the values using move semantics or copy and assignment.

Some key points about std::swap:

• It is templated, so it works for any type that supports copy/move
• It efficiently swaps values by moving rather than copying.
• Many C++ algorithms and containers use it to shuffle elements around.
• Specializations for some types like std::string and std::vector are provided to optimize performance.
• It provides a consistent way to swap objects without needing to rewrite swap code everywhere.

Some examples of using std::swap:

Example:

Let us take an example code in C++ that illustrates swapping two vectors using the std::swap() function.

Output:

Original Vector 1: 1 2 3 4 5
Original Vector 2: 10 20 30 40 50
Vectors after swapping:
Vector 1 (after swap): 10 20 30 40 50
Vector 2 (after swap): 1 2 3 4 5

Explanation:

In this example, the code defines two vectors, displays their original content, swaps them using std::swap(), and then displays the content of the vectors after the swap. Note that std::swap() is used to change all the vectors efficiently.

What is std::vector::swap?

The std::vector::swap member function of the std::vector class efficiently swaps the contents of one vector with another.

Syntax:

It has the following syntax:

It takes one argument - a reference to another std::vector to swap contents with.

Some key points about std::vector::swap:

• It swaps the contents by changing the internal pointers, sizes, capacities, etc. It makes it very efficient, as no actual data movement is required.
• The vectors must be of the same type (holding the same data type). Their current allocations can be different.
• It does not invalidate any references, pointers, and iterators referring to the elements in the vectors. The details are still the same; only their order has changed.
• It runs in constant O(1) time as it swaps internal members.

Example usage:

Example:

The following C++ code demonstrates how to swap two vectors using std::vector::swap().

Output:

Original Vector 1: 1 2 3 4 5
Original Vector 2: 10 20 30 40 50
Vectors after swapping:
Vector 1 (after swap): 10 20 30 4 5
Vector 2 (after swap): 1 2 3 40 50

Explanation:

Just like the previous example, the content of Vector 1 has been swapped with the range of Vector 2 using std::vector::swap().

Major key differences between std::swap and std::vector::swap

Here is a table summarizing the key differences between std::swap and std::vector::swap:

In summary, std::swap works for generic object swapping, while std::vector::swap leverages the vector's internal structure for an optimized, speedy vector shuffle, avoiding reallocation. The latter does not break any existing references into the vectors.

Conclusion:

In conclusion, std::swap exchanges any two objects by utilizing copy/move operations, while vector::swap leverages the vector's internal structure to efficiently shuffle contents in constant O(1) time without invalidating iterators.