Automatic object
An automatic variable is a variable whose value, behavior, or lifetime is managed implicitly by a programming language or shell rather than controlled entirely by the programmer.
Modern C
An automatic variable is a C variable whose storage is created on entry to its enclosing block and released when execution leaves that block.
- How it is used
- Explains when local objects exist, including across recursive calls and jumps within a block.
- How deep it goes
- Defines ordinary lifetimes, works through a compound-literal case, and illustrates storage setup; sets aside separate VLA and temporary-object rules.
- Examples
- Uses a goto-driven compound literal and its printed pointer comparison, then contrasts unoptimized and optimized assembler versions.
- What you can do after
- Evaluate/understand when an ordinary local object exists without mistaking its declaration or initialization for the start of its lifetime.
Modern C, Third Edition
An automatic variable is a C object with automatic storage duration, normally created on entry to a block and destroyed on exit from it.
- How it is used
- Explains local-object lifetime and pointer validity across block entry, recursion, and repeated execution.
- How deep it goes
- Works through block-lifetime rules and a compound-literal jump example, then illustrates stack setup without making it a language requirement.
- Examples
- Uses a `goto` loop, its printed pointer comparisons, and unoptimized and optimized assembler listings.
- What you can do after
- Diagnose/debug with it whether local objects and pointers remain valid across jumps, repeated evaluations, and recursive calls.
Read how Modern C, Third Edition explains automatic object →
Related concepts
- recursionproduced by · Recursion is a computational technique in which a definition or procedure refers to or invokes the same definition or procedure, directly or indirectly.
- lifetimeuses · A lifetime is the interval during which a program entity exists and remains valid or accessible under the applicable language rules.
- objectkind of · A computational object is a runtime entity or structured value representing data, state, or a resource, with properties or operations defined by its programming model.
- stackpart of · A stack is a data structure that adds and removes elements at one end, following last-in, first-out order.
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