Defines

Defines, in the context of programming, typically refer to preprocessor directives that introduce symbolic names or macros. The term is most associated with C and C++, where the preprocessor uses #define to substitute identifiers with literals or code fragments. Some languages provide similar constructs through constants or compile-time values rather than macros.

How defines work: The preprocessor runs before compilation, replacing occurrences of defined symbols with their values. Example: #define MAX 100 defines MAX as 100. Another example, #define SQUARE(x) ((x)*(x)), defines a macro that expands to the product. Conditional compilation is possible via #ifdef, #ifndef, #if, #else, and #endif. The directive #undef removes a definition.

Uses and trade-offs: Defines help avoid magic numbers, improve portability, and enable conditional compilation for different build configurations. However, they lack type safety, can cause unintended side effects if macros contain expressions, create hard-to-debug errors, and may lead to name clashes. Macros do not respect scope like regular variables and can complicate debugging.

Best practices: Wrap macro bodies in parentheses to avoid precedence issues, and avoid side effects in macro arguments. Prefer language-native facilities such as const, constexpr, or inline functions in modern C++ for type safety. Use include guards (#ifndef HEADER_H ... #define HEADER_H ... #endif) to prevent multiple inclusions of a header.

Alternatives and related concepts: Other ecosystems provide constants or enums managed by the language rather than preprocessor macros. For example, JavaScript uses const, while many languages rely on explicit constants or type-safe constructs rather than macros.