Opaque object
An opaque object is an object whose representation and contents are hidden and accessible only through specified operations.
Modern C
An opaque object is an object whose representation and contents can be accessed only through operations explicitly permitted by its abstraction.
- How it is used
- Uses opacity to reason about pointers and to separate library interfaces from hidden structure implementations.
- How deep it goes
- Defines permitted pointer operations and states, then explains forward declarations, stopping short of structure implementation details.
- Examples
- Uses string pointers, empty and null pointers, indeterminate pointers, and a forward-declared `struct toto` interface.
- What you can do after
- Evaluate C pointer states and design interfaces that conceal structure representations without hiding pointer semantics.
Modern C, Third Edition
An opaque structure is a C structure type whose complete member definition is hidden from code that uses its interface.
- How it is used
- Separates a library's public interface from its hidden structure implementation.
- How deep it goes
- Defines forward declarations, pointer use, representation rationale, and typedef visibility, but not the hidden structure's members.
- Examples
- Uses a forward-declared struct toto with get, destroy, and operation functions, plus pointer typedef alternatives.
- What you can do after
- Builds a client-facing C interface around a structure whose definition remains private to its implementation.
Related concepts
- referenceincludes · A reference is an indirect value or relationship that identifies or provides access to another value, object, resource, or source.
- structkind of · A struct is a composite data type or structure that groups related fields or values into a single unit.
- 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.
- missing valueused by · A missing value is a marker or condition indicating that an expected data value or reference is absent, unavailable, unknown, or inapplicable.
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