Question

I have few questions connected with struct and typedef, there is piece of code and I have marked some places where I’m not sure if the syntax is correct. I use Eclipse editor and it shows me when there is problem in compilation. I just don’t understand why is sometimes keyword struct needed and sometimes not. I may have also some mistakes of using this keyword. So plese help me to understand it.

let’s have struct

 typedef struct player
    {
        char *name; 
        int  gameId; 
        int  points; 
        int socketfd; //socket descriptor of player
        int state;
    } player_struct;

lets have another struct

#define PLAYERSLEN 2
typedef struct game{
    struct player_struct *players[PLAYERSLEN]; //PLACE1
    //some code

} game_struct;

let’s have function

player_struct *create_player()  //PLACE2
    {
    player_struct *player;  //PLACE3

    //alokace pameti
    player = (player_struct *) malloc(sizeof(player_struct)); //PLACE4
    //PLACE5

    player->gameId = -1;
    player->points = 0;
    player->state = 0;

    return player;
    }

let’s have function? In fact what does this definition mean?

void *( player_struct *player) //PLACE6
        {

        //some code

        }

Questions references:
PLACE1 – is this correct? why can’t I use just player_struct *players[PLAYERSLEN]; ??

PLACE2 – it looks like there is not needed struct before player_struct , is it correct? why?
PLACE3 – it looks like there is struct also not needed, is it correct? why?
PLACE4 – it looks like there is struct also not needed, is it correct? why?
PLACE4 & PLACE5 I may should handle errors there, cause there is malloc so I should probably put all the line with PLACE4 to if and if the malloc fails I should put at PLACE 5 free(player). Am I right?
PLACE6 what could have mean this function or whatever it is? The code inside brackets which is not included here should delete the player .. I just don’t understand the syntax of wrote function – what does it mean?
PLACE6 – again similar as previous why is not necessary put the keyword struct before player_struct at this line? is it correct?

Really thanks you for your time.

Answer 1

1. No. player_struct is a typedef for struct player. You don’t need the struct keyword in this case.
2. Correct. You created a type definition called player_struct which means struct player.
3. Same reason as 2.
4. Same reason as 2 & 3.
5. Yes, you should check to see if malloc() returns NULL. In addition, don’t cast the return value from malloc(). Doing so can hide #include errors.
6. That’s not a valid function definition. You don’t need struct because of the typedef – same as above.

You may find this all makes more sense if you remove the words typedef, player_struct, and game_struct from your code entirely. Then once you get used to how that all works, you can reintroduce the typedefs and maybe cut down on some typing. As a quick example, you can break down your first definition into its components:

struct player
{
  char *name; 
  int  gameId; 
  int  points; 
  int socketfd; //socket descriptor of player
  int state;
};

typedef struct player player_struct;

Maybe that will help you make sense of it?