How to use typedef in C++

In C++, the keyword typedef is used to create aliases for existing data types, to facilitate readability and maintenance of the code.

They are especially suitable for simplifying the declaration of complex types (such as those involving heavy use of pointers).

In addition to improving readability, they also facilitate portability across platforms (for example, by creating aliases for variable types with different names)

Basic Syntax

The basic syntax of typedef is as follows

typedef data_type alias_name;

For example,

typedef unsigned long ulong;

In this example,

• ulong becomes an alias for unsigned long, allowing the use of ulong instead of writing unsigned long each time.

Common Uses of typedef

Aliases for Simple Data Types

The most basic use of typedef is to create aliases for simple data types, such as int, char, float, etc.

typedef int integer;
typedef float real;
typedef char character;

Now, integer, real, and character can be used instead of int, float, and char, respectively.

Aliases for Pointers

typedef is especially useful for creating aliases for pointers, which can significantly improve readability.

typedef int* intPtr;

In this example, intPtr is an alias for int*.

Aliases for Structured Types

When working with structures (structs), typedef can greatly simplify usage and declarations.

typedef struct {
    int x;
    int y;
} Point;

Point p1;
p1.x = 10;
p1.y = 20;

In this example,

• Point is an alias for the anonymous structure
• It allows the use of Point directly to declare structure type variables

Complex Types and typedef

For more complex data types, such as function pointers or arrays, typedef can make declarations much more manageable.

Function Pointers

Declaring function pointers can be particularly confusing. typedef can simplify this task.

typedef void (*CallbackFunction)(int, int);

void myFunction(int a, int b) {
    std::cout << "a: " << a << ", b: " << b << std::endl;
}

int main() {
    CallbackFunction callback = myFunction;
    callback(5, 10);
    return 0;
}

In this example,

• CallbackFunction is an alias for a pointer to a function that takes two int and returns void

Arrays and Matrices

For arrays and matrices, typedef can also help us make declarations clearer.

typedef int Matrix3i[3][3];

Matrix3i matrix = {
    {1, 2, 3},
    {4, 5, 6},
    {7, 8, 9}
};

In this example, Matrix3i is an alias for a two-dimensional array (a matrix) of integers 3x3.