C++ Notes Help

typedef

typedef is used to create a type alias for an existing data type.

  • No new data type is created

  • Only an alternate name is given

typedef existing_type new_name; typedef int marks; marks m1, m2, m3; typedef int Integer; Integer x = 10; // same as int

typedef common usage

  1. Simplifying Complex Types

typedef unsigned long long ull; ull x = 100;

  1. typedef with Pointers (Important)

typedef int* IntPtr; IntPtr p1, p2; // both are pointers int* p1, p2; // p2 is NOT a pointer

  1. typedef with Arrays

typedef int Arr[10]; Arr a; // int a[10]

  1. typedef with Structs

// C-style: struct Student { int id; }; typedef struct Student Student; // Modern C++: struct Student { int id; }; // No typedef needed

  1. typedef with function pointers

typedef int (*Operation)(int, int); Operation add; // `add` is name of the function

Type checking is not stricter

MyInt a = 10; int b = a; // allowed

typedef works at compile time:

It’s resolved by the compiler. No runtime cost.

using

  • using creates a type alias.

  • Makes complex types and templates much more readable.

using NewName = ExistingType; using Integer = int; Integer x = 10; // same as int x = 10;

using common usage

  1. using with Pointers

using IntPtr = int*; IntPtr a, b; // both are int*

  1. using with Arrays

using IntArray = int[10]; IntArray arr; // int arr[10]

  1. using with function pointers

using Operation = int(*)(int, int); Operation add; // `add` is name of the function

  1. using with Templates (most important)

template<typename T> using Vec = std::vector<T>; Vec<int> v; // std::vector<int>

  • typedef can’t directly create template aliases

  • using can, which is why it’s preferred in modern C++

Type checking is not stricter

using MyInt = int; MyInt a = 10; int b = a; // allowed

using works at compile time

The alias is resolved by the compiler. No extra runtime overhead.

Last modified: 08 February 2026
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