Objective-C is an object-oriented language: it supports hierarchies of substitutable types, message-passing between objects, and code reuse through inheritance. Objective-C adds these features to the familiar C programming language.
Because Objective-C is an extension of C, many properties of an Objective-C program depend on the underlying C development tools. Among these properties are:
The size of scalar variables such as integers and floating-point numbers
Allowed placement of scoped declarations
Implicit type conversion and promotion
Storage of string literals
Preprocessor macro expansion
Compiler warning levels
Include and link search paths
For more information about these topics, consult the documentation for your development platform and tools.
Objective-C differs from C++, another object-oriented extension of C, by deferring decisions until runtime that C++ would make at compile time. Objective-C is distinguished by the following key features:
Object-oriented languages replace function calls with messages . The difference is that the same message may trigger different code at runtime, depending on the type of the message receiver. Objective-C decides dynamically—at runtime—what code will handle a message by searching the receiver's class and parent classes. (The Objective-C runtime caches the search results for better performance.) By contrast, a C++ compiler constructs a dispatch table ...