I was checking out a C tutorial on creating a server and got confused about the use of structs. In the header file, there's a struct definition like this:
`struct Server {`
`int domain;`
`int service;`
`int protocol;`
`u_long interface;`
`int port;`
`int backlog;`
`struct sockaddr_in address;`
`int socket;`
`struct Dictionary routes;`
`void (*register_routes)(struct Server *server, char *(*route_function)(void *arg), char *path);`
`};`
Then, in the main file, there's a function that looks like this:
`struct Server server_constructor(int domain, int service, int protocol, u_long interface, int port, int backlog) {`
`struct Server server;`
// ... (code for setting up server fields) ...
`return server;`
`}`
I'm a bit puzzled by the line `struct Server server;`. Is that a struct inside a constructor? Why do we need to write `struct` again? Can't we just write `Server server`?
3 Answers
It's basically creating a variable named `server` that is of type `struct Server`. When you're returning it, you're returning a complete struct of that type. In the header file, you define what the struct looks like, and the constructor just initializes its fields. If you want to simplify it to `Server server`, you have to use a typedef beforehand.
The statement `struct Server server` is just declaring a variable of type `struct Server`. To use `Server server` directly, you'd need to do something like `typedef struct Server Server;`. Some people prefer to keep the `struct` keyword for clarity, while others use typedef for brevity.
The `struct Server` you're seeing is just how C syntax works. When you define a struct like `struct Server`, you must declare variables of that type using the `struct` keyword, like `struct Server var;`. If you want to just use `Server`, you'd need to create a typedef for it. This is a key difference between C and C++ where you wouldn't need to do that. In C++, once you've defined `struct X`, writing `X` or `struct X` both work, thanks to the language rules there.
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