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The act of swapping two variables in computer programming refers to the exchange of the variables’ values. This is usually done using data stored in memory. For example, two variables in a program may be declared as follows (in pseudocode):

data_item x := 1
data_item y := 0

(x, y) swap

After swap(), x will have the value 0 and y will have the value 1; their values have been swapped. Other sorts of values, such as strings and aggregated data types, can be used with this operation. Swaps are used to shift the placements of data in comparison sorts.

Swap is a built-in function in several computer languages. Overloads are available in C++, allowing std::swap to swap some huge structures in O(1) time.

While this is a basic notion and in many circumstances the only practical technique to swap two variables, it consumes more RAM. Although this should not be an issue in most applications, the sizes of the values being swapped may be large (requiring a large temporary variable), or the swap operation may need to be repeated several times, as in sorting algorithms.

In addition, in object-oriented languages like C++, swapping two variables may need one call to the class constructor and destructor for the temporary variable, as well as three calls to the copy constructor. Some classes acquire memory in the constructor and then deallocate it in the destructor, resulting in costly system calls. Copy constructors for classes with a lot of data, such as an array, may require to manually copy the data.

The XOR operation is used to swap two numeric variables in XOR swap. It is usually seen to be faster than the above-mentioned naïve technique, although it does have drawbacks. In general, XOR swap is used to swap low-level data types like integers. It is, nevertheless, theoretically capable of exchanging any two values represented by fixed-length bitstrings.

Containers that use pointers to allocate memory from the heap can be swapped in a single operation by exchanging the pointers alone. This is most common in programming languages that enable pointers, such as C or C++. The Standard Template Library uses its built-in swap function to efficiently swap the contents of containers.

Because pointer variables are generally of a fixed size (e.g., most desktop computers have pointers that are 64 bits long) and are numeric, XOR swap can be used to swap them rapidly.

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