typedef and function pointer

Learn function pointer types with typedef.

typedef and function pointer

Function pointer syntax is long and hard to read. With typedef you give it a short, meaningful name.

Example: typedef int (*BinOp)(int, int);. This names a pointer to a function taking two ints and returning int as BinOp. From then on you write BinOp op = add; instead of the hard-to-read int (*op)(int, int) = add;. typedef with function pointers is the standard way to express dispatch tables and callbacks cleanly. The type name reflects its purpose; the code documents itself.

Using BinOp

After defining BinOp, you can assign any function with a matching signature. The call is simply op(a, b).

Example: define int add(int a, int b) { return a + b; }. Then assign with BinOp op = add;. Call with printf("%d\n", op(3, 4));; the result is 7. The pointer holds the function's address; the call is made directly. This is the clean way to choose which function to call at run time. The same BinOp type can represent addition, subtraction, multiplication, and more.

Exercise Write a typedef fp program

Define typedef int (*BinOp)(int, int);. Write int add(int a, int b) that returns a + b. In main assign BinOp op = add;. Call with printf("%d\n", op(3, 4));.

Show example solution

#include <stdio.h>

typedef int (*BinOp)(int, int);

int add(int a, int b) {
    return a + b;
}

int main(void) {
    BinOp op = add;
    printf("%d\n", op(3, 4));
    return 0;
}

Test yourself

Match the typedef fp parts

typedef

Naming
(*BinOp)

Pointer name
(int, int)

Parameter list
int

Return type
When is BinOp op = add; valid?
- When add takes two ints and returns int
- When add takes any parameters
- When add is defined inside main
- When add is declared static
Show answer

When add takes two ints and returns int — BinOp takes two ints and returns int; add must match that signature.
Complete the BinOp assignment
```
BinOp op = ____;
```
Show answer
```
BinOp op = add;
```

Next lesson: typedef and array

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