Auto
auto is a language feature that directs the compiler to deduce an object's type from its initializer.
Learn C++ by Example
Auto type deduction is the C++ language feature that lets the compiler infer a variable's type from its initializer.
- How it is used
- Uses type deduction to simplify variables, range-based loops, container code, generic addition, and selected function declarations.
- How deep it goes
- Explains deduction through expressions, containers, iterators, templates, and return types, while deferring fuller lambda and closure treatment.
- Examples
- Demonstrates arithmetic promotion, std::plus, vector iteration, Pascal's triangle, nested-vector returns, and generic lambdas.
- What you can do after
- Apply auto to simplify container programs, generic functions, range loops, and deduced function returns.
Modern C, Third Edition
auto is a C23 type-inference feature that allows an object's type to be inferred from its initializer.
- How it is used
- Supports type-generic declarations whose types must follow initializer expressions, especially inside macros and library-result handling.
- How deep it goes
- Explains initializer-based inference through SWAP and div examples, but does not enumerate the complete declaration constraint set.
- Examples
- Uses inferred arithmetic variables, a generic SWAP macro, and a div result exposing quotient and remainder members.
- What you can do after
- Apply it to maintain type consistency in generic declarations and to capture structure-valued results without spelling their types.
100 C++ Mistakes and How to Avoid Them
auto is a C++ declaration specifier that asks the compiler to deduce a variable's type from its initializer.
- How it is used
- Uses type inference to simplify variable, iterator, and loop declarations in modern C++.
- How deep it goes
- Explains initializer-based deduction and a signedness failure, but does not develop deduction rules beyond these practical cases.
- Examples
- Uses index loops, vector searches, iterator declarations, reverse iteration, and references returned from student names.
- What you can do after
- Evaluate/understand when deduction improves declarations and when an explicitly signed counter prevents unsigned wraparound.
Read how 100 C++ Mistakes and How to Avoid Them explains auto →
Related concepts
- C23contrasts with · C23 is the ISO standard revision of the C programming language published in 2024.
- type inferenceimplements · Type inference is the automatic deduction of program or expression types from available values, context, and constraints without requiring explicit type annotations.
- typeof operatoralternative to · A typeof operator obtains type information about an operand or expression, yielding a type or a string describing its type depending on the language.
- compileruses · A compiler is software that translates source code into executable code or another representation, while analyzing it according to the source language’s rules.
- trailing return typeuses · A trailing return type is C++ syntax that places a function's return type after its parameter list using an arrow.
- functionconfigures · A function is a callable program unit that performs an operation, may accept inputs, and can produce a result or side effect.
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