typedefs

Typedefs, or type aliases, are a feature in C and C++ that introduce alternative names for existing types. They do not create new types; they provide convenient or more descriptive names for existing ones, improving readability, portability, and ease of use with complex types.

In C, the syntax is typedef existing_type new_name;. For example, typedef unsigned long ulong; lets you write ulong count;. Typedef can also name structs or other compound types, such as typedef struct { int x; int y; } Point;, after which you can declare Point p;. It is also common to alias function pointer types for clarity, for example: typedef int (*Cmp)(const void*, const void*);.

In both C and C++, typedefs help when dealing with pointers, arrays, function pointers, or large composite types. They can simplify function signatures and make portable code that depends on platform-specific sizes more readable.

In modern C++, the preferred mechanism for type aliases is the using keyword, which can be more readable and supports alias templates. For example: using ulong = unsigned long;. Templates can be aliased with a construct like template <typename T> using Vec = std::vector<T>; This avoids some of the more cryptic syntax associated with typedef and is especially helpful with templates.

Common considerations include that typedefs do not create distinct types for type safety in the way some other language constructs might, and that qualifiers attach to the alias in predictable ways. Overall, typedefs remain a foundational tool for managing types, with using providing a clearer modern alternative in C++.