What is the difference between structure and structure using typedef with example?

Answer 1

Consider the following structure:

• struct data_t { /* ... */ };

The name of this type is struct data_t. This means that we must include the struct keyword whenever we declare any instances of the type or declare a pointer to the type:

• struct data_t object;
• struct data_t* ptr;

To remove the verbosity of the otherwise redundant structkeyword, we can use an alias:

• typedef struct data_t data;
• data object;
• data* ptr;

To simplify things further, we can combine the alias with the structure's definition:

• typedef struct data_t { /* ... */ } data;

Note that the _t suffix is conventionally used to denote a user-defined type as opposed to an alias. However, its usage is not consistent. For instance, the wchar_t type is not a type, it is implemented as an alias in the C standard library header:

• typedef unsigned short wchar_t;

In C++, the typedef keyword is not required; it is retained purely for backward compatibility with C. Aliases are introduced with the using keyword, never with typedef. We only use typedef when we are explicitly writing code intended for compilation under both C and C++.

Note also that wchar_t (amongst others) is a built-in type in C++, so we don't need to include the C standard library to make use of it, unless we are writing code for C.