stackallocated

Stackallocated is a term describing data that is allocated on the program’s call stack rather than on the heap. In languages with automatic storage duration, stackallocated values are created when entering a block or function and destroyed when control exits that scope. Their lifetime is tightly tied to the stack frame and cannot outlive the enclosing block.

Memory for stackallocated objects is typically allocated in the function’s stack frame, offering fast allocation and deallocation without explicit deallocation steps. Access tends to be cache-friendly due to spatial locality. Because the stack has a fixed size, stackallocated data is generally limited in magnitude and duration, and exceeding the limit can cause stack overflow or program crashes. This makes stackallocation well suited for small, short-lived objects and for temporary temporaries within a function.

Common examples include local variables and function parameters in languages such as C and C++. Some languages also support stack-allocated arrays or temporary buffers. In C, automatic variables are stackallocated by default, while C99 introduced variable-length arrays on the stack in some environments, and alloca can allocate on the stack at runtime. Other languages may distinguish stack versus heap storage more explicitly, with heap allocation typically required for data that must outlive the function scope or be shared beyond it.

Compared with heap allocation, stackallocation is cheaper and faster but riskier for large objects or long-lived data. It also constrains object lifetimes and complicates ownership and sharing in some languages. Developers often favor stackallocated storage for performance-critical, short-lived data while using heap allocation for dynamically sized or long-lived objects.