Understanding the Syntax of "typedef void Something" in C

The line typedef void Something in C is a type definition that creates an alias for a specific kind of function pointer. Here's a breakdown of its components and how it can be used in practical scenarios.

Purpose and Components

typedef: This keyword is used to create a new type name alias for an existing type. It simplifies the syntax of complex types.

void: This indicates that the function pointed to by the pointer does not return a value.

Something: This part defines Something as a pointer to a function. The parentheses around Something are necessary because of operator precedence. Without them, it would be interpreted incorrectly.

Empty parentheses: The empty parentheses indicate that the function takes no parameters.

Putting It All Together

So, typedef void Something means:

Something is a new type name for a pointer to a function that: Returns void, i.e., does not return a value. Takes no parameters.

Example Usage

Here’s how you might use this typedef in practice:

include stdio.h
// Define the typedef
 typedef void Something
// A function matching the typedef
void myFunction(){
    printf("Hello, World!
");
}
int main() {
    // Declare a variable of type Something
    Something funcPtr;
    // Assign the address of myFunction to funcPtr
    funcPtr  myFunction;
    // Call the function through the pointer
    funcPtr();
    return 0;
}

In this example, funcPtr is a pointer to a function that matches the signature defined by Something, allowing you to call myFunction through the pointer.

Understanding Typedef

Let's ignore the unbalanced parentheses. The line void Something declares Something as a type alias to a pointer to a function that takes variadic arguments from 0 to any number and returns void.

Memory Aids to Remember Typedef Usage

Consider the syntax used in typical declarations:

int i_t means i_t is declared as an int.
Put a typedef before it, and typedef int i_t means i_t is a type alias for int. Now, void Something declares Something as a function returning void. To declare a pointer to a function, use void (*Something), and to declare a typedef for it, use typedef void (*Something).

Usage in Code

Even if you hate empty argument lists in C and prefer to put a void there, you can still use it:

void somefunc(void) {
   …
}
…
typedef void (*Something)(void);
Something something_fn_ptr  somefunc;
// Invocation through the pointer
something_fn_ptr();