zeroinitialized

Zero-initialized, or zero-initialization, refers to the process by which a variable or a block of memory is set to the zero value appropriate for its type before it is used. For numeric types this is typically 0 (or 0.0 for floating-point types); for pointers it often corresponds to a null value, though the exact representation of a null pointer is not guaranteed to be all zeros by all language standards. Zero-initialization is distinct from other forms of initialization in that it aims to place a known, neutral value in memory immediately.

In C and C++, zero-initialization behavior is defined differently depending on storage duration and context. In C, objects with static storage duration that do not have an explicit initializer are zero-initialized. In C++, objects with static storage duration are also zero-initialized if not explicitly initialized. C++ also distinguishes between zero initialization and value initialization, with specific rules for scalar types, arrays, and class types. Dynamic memory allocation via malloc does not guarantee zeroing memory, while calloc does; in C++ one can rely on constructors to perform any needed initialization.

Other languages have their own conventions. Many managed languages allocate and initialize memory to zero or null by default: for example, Java initializes primitive numeric types to 0 and object references to null, while arrays of primitive types are filled with zeros. Rust requires explicit initialization for most memory, though it provides safe defaults and constructs for creating zeroed values where appropriate. Memory that must be zeroed for security or correctness, such as cryptographic keys, is often explicitly overwritten (zeroization) when no longer needed, to prevent sensitive data from remaining in memory.

Common considerations include portability of the null representation, performance implications of zeroing memory, and the distinction between static versus dynamic initialization across languages.