DevAcademia lesson/C++ Basics

Range-based For Loop

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~8 min lesson22 learning blocks5 code examples1 checks/interactions

Lesson outline

Modern Iteration

Introduced in C++11, the range-based for loop automatically iterates through all elements in a range without explicit counter management.

Works with raw arrays, std::array, STL containers, initializer lists, and user-defined types that are range-like (i.e., have begin/end member functions or free begin/end found by ADL).

Basic Usage

Modification Example

Maps & Structured Bindings (C++17)

When iterating key - value containers, structured bindings make code clearer.

Initializer Lists & Arrays

You can iterate braced lists and raw arrays directly.

C++20: Init-statement in Range-for

Since C++20, you can add an init-statement before the range declaration.

Supported Containers

Raw (C-style) arrays and std::array
STL containers (vector, string, list, deque, set, map, unordered_*)
Initializer lists (e.g., {1,2,3})
User-defined types with begin()/end() or free begin/end (ADL)
C++20 ranges/views that expose begin/end

Pitfalls & Tips

Iteration by value (auto x) copies each element; prefer const auto& for read-only, auto& for mutation.
Modifying the container (insert/erase) during iteration can invalidate references/iterators for some containers (e.g., vector, string).
If you need the index, use a traditional index-based loop or maintain a separate counter.
Order of iteration depends on the container (e.g., map is ordered by key; unordered_map has no defined order).
With proxy-reference containers like std::vector<bool>, use auto& to actually modify elements.

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