Which declaration demonstrates the proper typedef alias for a Point structure?

Which declaration demonstrates the proper typedef alias for a Point structure?

• A. typedef struct { int x; int y; } Point;
• B. struct Point { int x; int y; }
• C. typedef Point { int x; int y; } Point;
• D. typedef struct { int a; int b; } Point;

Answer: (A)

In C, to create a type alias for a struct you use typedef together with the struct definition. The correct way to define a Point type with x and y fields in one statement is: typedef struct { int x; int y; } Point; This defines an anonymous struct and then makes Point an alias for that type, so you can declare variables simply as Point p; and access p.x and p.y. The other forms don’t provide a typedef alias for Point. Declaring a struct with a tag named Point means you’d use struct Point p; rather than Point p;, unless you also typedef that struct. A declaration that tries to typedef a Point in front of its definition using that syntax isn’t valid C. And a version that defines an anonymous struct and typedefs it to Point but with fields named a and b would create a Point type with different members, not the intended x and y.

In C, to create a type alias for a struct you use typedef together with the struct definition. The correct way to define a Point type with x and y fields in one statement is: typedef struct { int x; int y; } Point; This defines an anonymous struct and then makes Point an alias for that type, so you can declare variables simply as Point p; and access p.x and p.y.

The other forms don’t provide a typedef alias for Point. Declaring a struct with a tag named Point means you’d use struct Point p; rather than Point p;, unless you also typedef that struct. A declaration that tries to typedef a Point in front of its definition using that syntax isn’t valid C. And a version that defines an anonymous struct and typedefs it to Point but with fields named a and b would create a Point type with different members, not the intended x and y.