Function pointer type
A function pointer is a value that designates a callable function and can be stored, passed, or invoked indirectly.
Modern C
A function pointer is a pointer value that designates a function and can be passed to or invoked by other code.
- How it is used
- Deploys function pointers for callbacks, generic searching and sorting, selectable logging behavior, and thread entry functions.
- How deep it goes
- Explains decay, declaration syntax, invocation forms, generic callbacks, and exact type matching, with detailed comparison examples.
- Examples
- Uses atexit declarations, equivalent calls, qsort comparisons, logging tables, and thrd_create callbacks as concrete examples.
- What you can do after
- Apply it via C callback interfaces, typedef readable signatures, implement comparison functions, and select functions through pointer variables or tables.
Modern C, Third Edition
A function pointer is a C pointer value that designates a function and can be used to invoke or pass that function indirectly.
- How it is used
- Deploys function pointers for indirect calls, callbacks, generic algorithms, configurable behavior, and thread entry functions.
- How deep it goes
- Explains decay, declaration syntax, equivalent calls, callback contracts, and exact matching, while stopping short of broader pointer internals.
- Examples
- Uses equivalent call expressions, qsort and bsearch comparison functions, configurable loggers, and thrd_create callbacks.
- What you can do after
- Build callback-based C interfaces and apply qsort, bsearch, logging, or thread creation with correctly matched function types.
Read how Modern C, Third Edition explains function pointer type →
Refactoring to Rust
A function pointer is a value that refers to a callable function and can be passed as an argument or stored for later invocation.
- How it is used
- Uses function pointers to register callbacks across the NGINX HTTP FFI boundary.
- How deep it goes
- Defines the Rust and C callback signatures and demonstrates invocation, but defers general function-pointer behavior beyond this FFI case.
- Examples
- Demonstrates `read_body_handler` passed as `Some(...)` to NGINX request-body parsing.
- What you can do after
- Apply it via Rust FFI by declaring a C-compatible callback type and passing a matching handler to an API.
Read how Refactoring to Rust explains function pointer type →
Rust in Action: Systems programming concepts and techniques
A function pointer is a value that identifies a function and can be passed or stored so that the function can be invoked indirectly.
- How it is used
- Supplies callbacks that an operating system can invoke, particularly registered signal handlers.
- How deep it goes
- Explains executable-code addresses, pointer casts, and function signatures through small programs; does not develop a general callback API.
- Examples
- Uses an address-printing `noop` program and a `libc::signal` shutdown-handler program.
- What you can do after
- Apply it via `libc::signal` to register a handler and recognize why the example casts its function address.
Related concepts
- function decayproduced by · Function decay is the C conversion of a function designator to a pointer to that function except in contexts such as sizeof and unary &.
- callused by · A function call is an operation or expression that invokes a function or other callable, optionally supplies arguments, and initiates its execution.
- referencekind of · A reference is an indirect value or relationship that identifies or provides access to another value, object, resource, or source.
- closurecontrasts with · A closure is a function or callable value together with access to bindings from the lexical environment in which it was created.
- callbackused by · A callback is a function or other callable supplied to software for invocation later in response to a specified event, condition, or point in execution.
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