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:

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

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This is the header

Code:

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// 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;
};

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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:

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

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

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

Code:

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

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but i get this error though

Code:

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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

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Code:

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

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Should do it.

Quote:

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Originally Posted by Elysia

Code:

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

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Should do it.

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Why wouldn't this be:

Code:

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

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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:

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

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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:

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#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;
}

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Quote:

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Originally Posted by Todd Burch

I ran a test instead of guessing.

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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?

Quote:

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Originally Posted by vart

It was not a guess

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I think he was referring to Elysia rather than yourself.

Quote:

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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?

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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:

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#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;
}

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Todd

Quote:

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Originally Posted by iMalc

I think he was referring to Elysia rather than yourself.

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Actually, I was referring to myself. :)

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

Code:

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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

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Quote:

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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

---

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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.

thanks again guys! i might not drop this course at all... i was about to :( i've been stuck for 2.5 days

Code:

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    rooms[num_rooms-1].description = "test element before last";
    printf(rooms[num_rooms-1].description);
    printf("%\n");
    rooms[num_rooms].description = "test element last";
    printf(rooms[num_rooms].description);
    printf("%\n");
    rooms[0].description = "test element 1";
    printf(rooms[0].description);
    printf("%\n");

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works

Quote:

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Originally Posted by NoobieGecko

thanks again guys! i might not drop this course at all... i was about to :( i've been stuck for 2.5 days

Code:

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    rooms[num_rooms-1].description = "test element before last";
    printf(rooms[num_rooms-1].description);
    printf("%\n");
    rooms[num_rooms].description = "test element last";
    printf(rooms[num_rooms].description);
    printf("%\n");
    rooms[0].description = "test element 1";
    printf(rooms[0].description);
    printf("%\n");

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works

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No it doesn't. Read up on array indices again.

you're right, I get blanks, why is that?
i'm going to try to malloc for character size to see if it works...

Code:

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    if (rooms==NULL){
        printf("panic");
    }

    rooms[num_rooms-1].description = "test element before last";
    rooms[num_rooms].description = "test element last";
    rooms[0].description = "test element 1";

    //printf(rooms[num_rooms-1].description);
    printf("%\n");
    rooms[num_rooms].description = "test element last";
    //printf(rooms[num_rooms].description);
    printf("%\n");
    rooms[0].description = "test element 1";
    //printf(rooms[0].description);
    printf("%\n");

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Arrays start from 0, so if you request space for 10 structs, you get structs elements from 0 to 9.

1. if you allocate num_rooms elements - you can access indexes from 0 to num_rooms-1

rooms[num_rooms] will access out of bounds memory

2. if you want do like this
rooms[num_rooms-1].description = "test element before last";

declare description as const char* pointer

3. to print it use
printf("%s", rooms[0].description );

Thanks:

Code:

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    rooms[num_rooms-1].description = "test element last";
    rooms[0].description = "test element 1";

    printf("%s", rooms[num_rooms-1].description);
    printf("\n");
    printf("%s", rooms[0].description);
    printf("\n");

---

output:
test element last
test element 1

i might have to ask u guys more questions later, is that okay? i'm working on the next part! thanks again!

Sure. You got question, you ask them and we answer them.
It's a good thing. You'll learn plenty.

Quote:

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Originally Posted by Todd Burch

Code:

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printf("sizeof(room) = %d\n", sizeof(myroom) );

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sizeof returns size_t, so use %zu instead:

Code:

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printf("sizeof(room) = %zu\n", sizeof(myroom) );

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Quote:

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Originally Posted by robwhit

sizeof returns size_t, so use %zu instead:

Code:

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printf("sizeof(room) = %zu\n", sizeof(myroom) );

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I can't find %z. What's %z? Got a link?

Todd

Quote:

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Originally Posted by Todd Burch

I can't find %z. What's %z? Got a link?

Todd

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From man printf:

Quote:

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z

A following integer conversion corresponds to a size_t or ssize_t argument. (Linux libc5 has Z with this meaning. Don't use it.)

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OK, I didn't find it under man printf, but did find it under man 3 printf.

Thanks.

Note that z is not C89, but C99.