What does this typedef mean?

Question

I am new to C, and this typedef looks a little bit strange to me. Can someone explain what it does?

typedef void (*alpm_cb_log)(alpm_loglevel_t, const char *, va_list);

It is in a header file.

Answer 1

You can use cdecl.org : http://cdecl.ridiculousfish.com/?q=void+%28*alpm_cb_log%29%28alpm_loglevel_t%2C+const+char+*%2C+va_list%29+

It says:

declare alpm_cb_log as pointer to function (alpm_loglevel_t, pointer to const char, va_list) returning void

in this case, it is a typedef, not a declaration.

Answer 2

It defines alpm_cb_log to be a type for a pointer to a function that takes the arguments alpm_loglevel_t, const char *, va_list and returns void.

Answer 3

A Simple example. Declaration:

typedef int myint.

Use:

myint number = 7;

myint is a synonym of int.

your example

typedef void (*alpm_cb_log)(alpm_loglevel_t, const char *, va_list);

this is a pointer to a function

(*alpm_cb_log)

The arguments are

(alpm_loglevel_t, const char *, va_list)

and does not return anything.

void 

The general rule with the use of typedef is to write out a declaration as if you were declaring variables of the types that you want

Answer 4

These do look weird if you've never seen them before. It's a typedef alpm_cb_log for a pointer to a function returning void, taking two or more arguments: an alpm_loglevel_t, a const char *, and a variable argument list.

Answer 5

it creates the alais alpm_cb_log which is a pointer to a function that returns void and takes three paramaters. 1. a alpm_loglevel_t 2. const char *. 3 a varaibale argument list.