Unsafe block
An unsafe block is a Rust code region that permits operations whose safety requirements the compiler cannot verify and whose correctness requires programmer responsibility.
Refactoring to Rust
An unsafe block is a Rust block that permits operations requiring an unsafe context, with the programmer responsible for upholding their safety conditions.
- How it is used
- Enables operations needed when Rust handles pointers and memory across a C FFI boundary.
- How deep it goes
- Defines the permitted operations and works through pointer dereferences, null checks, and C-string conversion; does not elaborate the other operations.
- Examples
- Uses vector pointer arithmetic, a C calculator’s output pointer, and conversion of its input C string.
- What you can do after
- Apply it via Rust’s `unsafe` blocks to dereference raw pointers and handle C-provided values while taking responsibility for validity.
Rust in Action: Systems programming concepts and techniques
An unsafe block is a Rust code region in which operations requiring explicit programmer responsibility for safety are permitted.
- How it is used
- Uses unsafe blocks to examine bit representations and process memory while making programmer responsibility for safety explicit.
- How deep it goes
- Defines the safety responsibility and works through transmute and raw-pointer dereferencing, but does not provide a comprehensive unsafe-operation reference.
- Examples
- Shows an `f32`–`u32` transmute round trip and a byte-by-byte memory scan that crashes at address zero.
- What you can do after
- Practice/perform contained unsafe operations while recognizing that permission to dereference a pointer does not establish a readable address.
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Learn Rust in a Month of Lunches
An unsafe block is a Rust code block that permits operations requiring the programmer to uphold safety invariants that the compiler cannot verify.
- How it is used
- Uses unsafe blocks to mark operations involving unsafe functions, foreign-language interfaces, low-level resources, and mutable statics.
- How deep it goes
- Explains the safety boundary and compiler corrections, then demonstrates data races without developing unsafe-code internals.
- Examples
- Demonstrates an unsafe function call and concurrent increments of a mutable static producing inconsistent totals.
- What you can do after
- Apply unsafe blocks to call unsafe functions and access mutable statics while recognizing the responsibility for preventing undefined behavior.
Read how Learn Rust in a Month of Lunches explains unsafe block →
Related concepts
- static mutused by · static mut is a Rust declaration for mutable statically allocated storage with a program-wide lifetime, whose access requires unsafe handling.
- raw pointeruses · A raw pointer is a value that represents a memory address and can be dereferenced without the validity and aliasing guarantees provided by a managed reference.
- referenceused by · A reference is an indirect value or relationship that identifies or provides access to another value, object, resource, or source.
- unsafe Rustconfigured by · Unsafe Rust is Rust code that permits operations whose safety conditions the compiler cannot fully verify and that therefore require the programmer to uphold the relevant invariants.
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