typedef struct vs struct in C: What's the Difference?

By the end of this page, you'll understand what a struct tag is in C, what typedef does, and why these two declarations look similar but are not exactly the same. You'll also learn the syntax developers use in real C codebases and how to choose the right form for readability and maintainability.

In C, struct and typedef solve related but different problems.

• struct defines a structure type.
• typedef creates an alias name for an existing type.

That means these are not identical operations.

1. Defining a struct without typedef

struct myStruct {
    int one;
    int two;
};

This creates a structure type with the tag myStruct.

To declare variables of that type, you must write:

struct myStruct a;

Notice that in C, the word struct is part of the type name when you use the tag.

2. Defining a struct with typedef

 
     one;
     two;
} myStruct;

Think of struct and typedef like a person and a nickname.

• struct myStruct is the person's full formal name.
• typedef ... myStruct is giving that type a shorter nickname.

If you only create the formal name, you must always use the full name:

struct myStruct x;

If you only create the nickname, you use the nickname:

myStruct x;

If you create both, you can use either one.

Another way to think about it:

• struct creates the actual structure type definition.
• typedef creates a label you can use instead of the original type spelling.

typedef does not create a new kind of data by itself. It only gives an existing type another name.

Core syntax

Struct with a tag only

struct Point {
    int x;
    int y;
};

struct Point p1;

Here, Point is a struct tag. You must write struct Point when declaring variables.

Typedef with an anonymous struct

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

Point p1;

Here, Point is a typedef alias. You use Point directly.

Typedef with a tagged struct

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

Point p1;
struct Point p2;

Consider this example:

#include <stdio.h>

typedef struct {
    int one;
    int two;
} MyStruct;

int main(void) {
    MyStruct a;
    a.one = 5;
    a.two = 7;

    int total = a.one + a.two;
    printf("%d\n", total);
    return 0;
}

Step by step

1. The struct type is defined

typedef struct {
    int one;
    int two;
} MyStruct;

• A struct is defined with two members: one and two
• MyStruct becomes a typedef alias for that struct type

2. A variable is declared

MyStruct a;

• Memory is reserved for one struct variable named

Structures are used whenever you need to group related data together.

Common examples

User records

typedef struct {
    int id;
    char name[50];
} User;

Used in:

• command-line tools
• file parsing
• database-like records in memory

2D points or geometry

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

Used in:

• graphics programs
• games
• coordinate calculations

Configuration data

typedef struct {
    int port;
    int debug;
} Config;

Used in:

• application settings
• server startup options
• embedded systems

API response models

 
     status;
     message[];
} Response;

In real C projects, the choice between struct X and typedef struct ... X often depends on team style, API design, and compatibility needs.

Common patterns

1. Public data models in header files

Libraries often use typedefs so users of the library get simple names:

typedef struct {
    int code;
    char text[64];
} ErrorInfo;

This keeps function signatures short:

ErrorInfo get_last_error(void);

2. Opaque structs for encapsulation

A common C pattern is to expose only a forward declaration in a header:

typedef struct FileHandle FileHandle;

The full struct definition is hidden in a .c file. This lets developers use pointers without seeing internal fields:

FileHandle *open_file(  *path);

1. Thinking typedef creates a new struct kind

typedef does not create a brand new data structure. It only creates another name for a type.

typedef int Number;

Number is still just int.

The same idea applies to structs.

2. Mixing up tag names and typedef names

Broken example:

typedef struct {
    int one;
    int two;
} MyStruct;

struct MyStruct a;  // wrong

Why it fails:

• MyStruct here is a typedef alias
• There is no struct tag named MyStruct

Correct:

MyStruct a;

Or define both:

Quick rules

• struct X { ... }; defines a struct tag named X
• Use it as struct X variable;
• typedef struct { ... } X; creates a typedef alias named X
• Use it as X variable;
• typedef struct X { ... } X; gives you both forms

Common patterns

Tag only

struct Person {
    int age;
};

struct Person p;

Typedef only

typedef struct {
    int age;
} Person;

Person p;

Tag + typedef

typedef struct Person {
    int age;
} Person;

Person p1;

What is the difference between struct and typedef struct in C?

struct defines a structure type with a tag, while typedef gives a type another name. A plain struct must be used as struct Name, but a typedef alias can be used as Name.

Does typedef struct create a new type?

Not in the same sense as defining a new kind of data. It creates an alias for a type. The underlying struct type is still the same.

Why do C programmers often use typedef with structs?

Mostly for convenience and readability. It removes the need to write struct every time the type is used.

Can I use struct MyType after typedef struct { ... } MyType;?

No. That form creates a typedef alias but no struct tag named MyType.

When should I use typedef struct Name { ... } Name;?

Use it when you want both a struct tag and a short alias. This is common in larger C projects and libraries.

Is this different in C++?

• struct in C — The core feature for grouping related data.
• typedef in C — Needed to understand how aliases work for any type, not just structs.
• pointers to structs — Common because structs are often passed by pointer in functions.
• self-referential structs — Important for linked lists, trees, and graph nodes.
• forward declarations — Often used with struct tags in headers.
• header files in C — Struct and typedef declarations are commonly placed in headers.
• opaque pointers — A real-world pattern that often depends on typedef and forward-declared structs.
• C vs C++ struct syntax — Useful because beginners often mix the two languages.