Stuck, arrays

I thought that I did this the right way, but it turns out I can't allocate more than 1 size of an array. (I'm supposed to initialize a room_array data structure which is an array of structs).

I have this syntax.

Code:

    int size_room = sizeof(struct room);
    room_t **room_structs  = (room_t **)malloc(num_rooms * size_room);

This is the header

Code:

// a struct containing all the information which represents a room
struct room {
    int room_id;
    char *description;
    mob_t mob;
    exit_t exits[NUM_DIRECTIONS];
    puzzle_t puzzle;
};

this is a follow up from my last post, can anyone help me? I've been stuck since 7 pm

you do not need to cast malloc in C
dynamical array of structs is allocated as

Code:

struct Node* pNodes = malloc(numOfNodes * sizeof *pNodes);

your pointer to pointer notation is not suitable for one-dimentional array

So the array is Node, not pNodes? Am I right?

Code:

room_t room_structs* room  = malloc(num_rooms * (sizeof room));

but i get this error though

Code:

gcc -std=c99 -g -Wall -c -o obj/level.o level.c
level.c: In function `load_level':
level.c:39: error: syntax error before '*' token

Code:

struct room_t room_structs* room  = malloc(num_rooms * (sizeof room));

Should do it.

Originally Posted by Elysia

Code:

struct room_t room_structs* room  = malloc(num_rooms * (sizeof room));

Should do it.

Why wouldn't this be:

Code:

struct room * room_structs = malloc(num_rooms * sizeof(room)) ;

room is the type of the structure. I don't see a room_t. And, can you reuse room for a variable name of struct room?

Todd

OK, to get rid of confusion, once more:

Code:

struct room* rooms = malloc(num_rooms * sizeof(room));

Sometimes I just scan through not double-checking it's right.

not sizeof room

or (better)
sizeof *rooms

or (not so good, but also will work)
sizeof (struct room)

I ran a test instead of guessing.

Final word.

Code:

#include <stdio.h>

// a struct containing all the information which represents a room
struct room {
	int room_id;
	char *description;
	int mob;
	double exits[10];
	char * puzzle;
} myroom, *room_ptr ;


int main (int argc, const char * argv[]) {

    printf("sizeof(myroom) = %d\n", sizeof(myroom) );            // Use this... 
    printf("sizeof(struct room) = %d\n", sizeof(struct room) );  // Or this. 

    printf("sizeof(room_ptr) = %d\n", sizeof(room_ptr) );    // But not this.. 
    //printf("sizeof(* myroom) = %d\n", sizeof(* myroom) );  // and this generates a compile error 
    //printf("sizeof(* room) = %d\n", sizeof(* room) );      // and so does this.
    return 0;
}

Originally Posted by Todd Burch

I ran a test instead of guessing.

It was not a guess

You a missing

sizeof (*room_ptr );

How could you ran tests if you fail to read the simple line of code?

Originally Posted by vart

It was not a guess

I think he was referring to Elysia rather than yourself.

Originally Posted by vart

It was not a guess

You a missing

sizeof (*room_ptr );

How could you ran tests if you fail to read the simple line of code?

A little testy today, aren't we?

Every test shown above I ran. And yes, I missed this one. Thank you for pointing out my omission.

Code:

#include <stdio.h>

// a struct containing all the information which represents a room
struct room {
	int room_id;
	char *description;
	int mob;
	double exits[10];
	char * puzzle;
} myroom, *room_ptr ;


int main (int argc, const char * argv[]) {

    printf("sizeof(room) = &#37;d\n", sizeof(myroom) );              // Use this... 
    printf("sizeof(struct room) = %d\n", sizeof(struct room) );  // Or this, 
    printf("sizeof(* room_ptr) = %d\n", sizeof(* room_ptr) );    // Or this.

    printf("sizeof(room_ptr) = %d\n", sizeof(room_ptr) );    // But not this.. 
    //printf("sizeof(* myroom) = %d\n", sizeof(* myroom) );  // and this generates a compile error 
    //printf("sizeof(* room) = %d\n", sizeof(* room) );    // and so does this.
    return 0;
}

Todd

Originally Posted by iMalc

I think he was referring to Elysia rather than yourself.

Actually, I was referring to myself.

Thanks guys, you are all awesome!
Anyway I tried this:

Code:

struct room* rooms = malloc(num_rooms * sizeof(struct room));

int siz = sizeof(rooms)/sizeof(rooms[0]);
printf("%d", siz);
// I'm trying to get how many rooms i can store inside rooms
// Because I'm trying to initialize each sub struct for each room inside rooms(character_id, exits, puzzle)
// To null
// But I get a zero for siz
// And a 4 for sizeof(rooms)
// How do I call rooms[0], rooms[1], etc.?
// if rooms[0] = is a room

Originally Posted by NoobieGecko

Thanks guys, you are all awesome!
Anyway I tried this:

Code:

struct room* rooms = malloc(num_rooms * sizeof(struct room));

int siz = sizeof(rooms)/sizeof(rooms[0]);
printf("%d", siz);
// I'm trying to get how many rooms i can store inside rooms
// Because I'm trying to initialize each sub struct for each room inside rooms(character_id, exits, puzzle)
// To null
// But I get a zero for siz
// And a 4 for sizeof(rooms)
// How do I call rooms[0], rooms[1], etc.?
// if rooms[0] = is a room

I would guess that since rooms is a pointer, sizeof(rooms)==4; and since we're doing integer arithmetic, 4/(some number larger than 4) gives zero. You don't need to know siz, you've already got it, it's num_rooms.

Edit to add: If you're worried that maybe you didn't get all the memory you asked for, you should recall that malloc returns NULL (instead of a valid pointer) if the memory allocation didn't succeed. So if (rooms==NULL) you need to panic; otherwise, you have all the memory you asked for.