[Term entry] C++Sets Swap()

content/cpp/concepts/sets/terms/swap/swap.md

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+---
+Title: 'swap()'
+Description: 'Exchanges the contents of two sets.'
+Subjects:
+  - 'Code Foundations'
+  - 'Computer Science'
+Tags:
+  - 'Containers'
+  - 'Sets'
+CatalogContent:
+  - 'learn-c-plus-plus'
+  - 'paths/computer-science'
+---
+
+**`swap()`** exchanges the contents of two `std::set` containers (or two compatible ordered associative containers). This operation is typically faster than copying or moving elements individually, as it swaps internal pointers and metadata without modifying or relocating the actual elements.
+
+## Syntax
+
+```pseudo
+set1.swap(set2);
+```
+
+Or using the non-member function:
+
+```pseudo
+std::swap(set1, set2);
+```
+
+**Parameters**
+
+- `set1`, `set2`: Two `std::set` containers of the same type (including the same key type, comparator, and allocator).
+
+**Return value:**
+
+- The function does not return anything. It simply swaps the contents.
+
+## Example
+
+In this example, `std::swap()` is used to exchange the contents of two integer sets named `odds` and `evens`:
+
+```cpp
+#include <iostream>
+#include <set>
+#include <algorithm>
+
+int main() {
+  std::set<int> odds  {1, 3, 5, 7};
+  std::set<int> evens {2, 4, 6, 8};
+
+  std::cout << "Before swap → odds: ";
+  for (int n : odds)  std::cout << n << ' ';
+  std::cout << "| evens: ";
+  for (int n : evens) std::cout << n << ' ';
+  std::cout << '\n';
+
+  std::swap(odds, evens);   // non‑member swap
+
+  std::cout << "After  swap → odds: ";
+  for (int n : odds)  std::cout << n << ' ';
+  std::cout << "| evens: ";
+  for (int n : evens) std::cout << n << ' ';
+  std::cout << '\n';
+}
+```
+
+The output of this code is:
+
+```shell
+Before swap → odds: 1 3 5 7 | evens: 2 4 6 8
+After  swap → odds: 2 4 6 8 | evens: 1 3 5 7
+```
+
+## Codebyte Example
+
+In this example, the member function `swap()` is used to swap the contents of two string sets, `a` and `b`:
+
+```codebyte/cpp
+#include <iostream>
+#include <set>
+#include <algorithm>
+
+int main() {
+  std::set<std::string> a {"apple", "banana"};
+  std::set<std::string> b {"carrot", "date", "eggplant"};
+
+  auto dump = [](const std::string& label, const std::set<std::string>& s){
+    std::cout << label << ": ";
+    for (const auto& v : s) std::cout << v << ' ';
+    std::cout << '\n';
+  };
+
+  dump("a", a);
+  dump("b", b);
+
+  a.swap(b); // member swap
+
+  std::cout << "\nAfter swap\n";
+  dump("a", a);
+  dump("b", b);
+}
+```