C typedef
C typedef
The typedef keyword lets you create a new name (an alias) for an existing type.
This can make complex declarations easier to read, and your code easier to maintain.
For example, instead of always writing float, we can create a new type called Temperature to make the code clearer:
Example
#include <stdio.h>
typedef float Temperature;
int main() {
Temperature today = 25.5;
Temperature tomorrow = 18.6;
printf("Today: %.1f C\n", today);
printf("Tomorrow: %.1f C\n", tomorrow);
return 0;
}
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Here, Temperature is just another name for float. However, the code is more expressive: it tells us that these numbers are temperatures, not just any floating-point numbers.
Why Use typedef?
- Simplifies code: Shorter, easier-to-read type names.
- Improves clarity: Expresses intent better (for example,
AGEinstead of justint). Also helps avoid confusion when many variables share the same base type (likefloatordouble).
Good To Know: In modern C, typedef is often used together with struct, enum, and function pointers to keep code clean and easier to read.
typedef with struct
typedef can be useful with struct, because it lets you avoid writing struct every time:
Example
#include <stdio.h>
// Without typedef:
struct Car {
char brand[30];
int year;
};
// With typedef:
typedef struct {
char brand[30];
int year;
} Car;
int main() {
struct Car car1 = {"BMW", 1999}; // needs "struct"
Car car2 = {"Ford", 1969}; // shorter with typedef
printf("%s %d\n", car1.brand, car1.year);
printf("%s %d\n", car2.brand, car2.year);
return 0;
}
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This example shows how typedef makes it easier to work with multiple struct variables, like different car models:
Example
#include <stdio.h>
// With typedef
typedef struct {
char brand[30];
char model[30];
int year;
} Car;
int main() {
Car car1 = {"BMW", "X5", 1999};
Car car2 = {"Ford", "Mustang", 1969};
Car car3 = {"Toyota", "Corolla", 2011};
printf("%s %s %d\n", car1.brand, car1.model, car1.year);
printf("%s %s %d\n", car2.brand, car2.model, car2.year);
printf("%s %s %d\n", car3.brand, car3.model, car3.year);
return 0;
}
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Here you can see how typedef keeps the code clean when structs are nested inside other structs:
Example
#include <stdio.h>
// Define three structs with typedef
typedef struct {
char firstName[20];
char lastName[20];
} Owner;
typedef struct {
char brand[20];
int year;
Owner owner;
} Car;
typedef struct {
char name[30];
Car featuredCar;
} Dealership;
int main() {
Owner person = {"John", "Doe"};
Car car1 = {"Toyota", 2010, person};
Dealership d = {"City Motors", car1};
printf("Dealership: %s\n", d.name);
printf("Featured Car: %s (%d), owned by %s %s\n",
d.featuredCar.brand,
d.featuredCar.year,
d.featuredCar.owner.firstName,
d.featuredCar.owner.lastName);
return 0;
}
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It is up to you whether you want to use typedef or not.
Your code will work the same without it. However, in modern C it is often used to make code shorter, clearer, and easier to maintain.
