Are typedef and #define the same in C?

No, typedef and #define are not the same in C; they serve distinct purposes and exhibit different behaviors.

#define

#define is a preprocessor directive in C used for defining macros. It can define constant values or macro functions. Preprocessor directives are executed before compilation and perform only text substitution.

Example:

c
#define PI 3.14159
#define MAX(a, b) ((a) > (b) ? (a) : (b))

int main() {
    double circle_area = PI * radius * radius;
    int max_val = MAX(3, 5);  // replaced by ((3) > (5) ? (3) : (5))
}

In the above example, PI and MAX are replaced by their respective values or expressions before compilation. They do not introduce new types; they are purely text substitutions.

typedef

typedef is used to define type aliases. It is processed at compile time, assigning a new name to an existing data type, typically to simplify complex type declarations or improve code readability.

Example:

c
typedef unsigned long ulong;
typedef struct {
    int x;
    int y;
} Point;

int main() {
    ulong number = 5000;
    Point p1 = {10, 20};
}

In the above example, ulong is an alias for unsigned long, and Point is an alias for a struct type. Using typedef allows programmers to use these types more conveniently without repeating the full definition.

Summary

• #define is a preprocessor directive used for text substitution, which can define macros or constants.
• typedef is used to define type aliases, making the code clearer and easier to manage.
• #define lacks type awareness, whereas typedef is closely tied to types.
• Using typedef can enhance type safety.

Therefore, although both can define aliases to some extent, their usage scenarios and purposes are significantly different.