Thread: Realloc does not work as intened...

Hey,

I have got the following code:

Code:

/* Adds a move string to a MOVE_DATA * If there is no more space left, space of the MOVE_DATA will be doubled.
 * Returns 1, if successful
 * Returns 0, OutOfMemoryException
 */
char add_move_to_data(MOVE_DATA* move_info, char* move){
    if(move_info->array_size == move_info->used_array_size){
        printMoves(move_info->moves, move_info->used_array_size, 0);
        printf("\n");
        char* p= realloc(move_info->moves, 2*(move_info->array_size));
        move_info->array_size = 2*(move_info->array_size);
        if(!p){
            return 0;
        } else {
            move_info->moves = (char**)p;
        }
        printMoves(move_info->moves, move_info->used_array_size, 0);
    }
    move_info->moves[move_info->used_array_size++] = move;
    return 1;
}

With the strcuture:

Code:

typedef struct {    char** moves;
    size_t array_size;
    size_t used_array_size;
} MOVE_DATA;

After reallocating the char**, there is only a small amount of the moves printable:

Before:
Move: 009,017,000,
Move: 010,018,000,
Move: 011,019,000,
Move: 012,020,000,
Move: 013,021,000,
Move: 014,022,000,
Move: 014,023,000,
Move: 016,024,000,
Move: 016,032,000,
Move: 016,040,000,
Move: 016,048,000,
Move: 016,017,000,
Move: 016,018,000,
Move: 016,019,000,
Move: 016,020,000,
Move: 016,021,000,
Move: 016,022,000,
Move: 016,023,000,
Move: 063,055,000,

After:

Move: 009,017,000,
Move: 010,018,000,
Move: 011,019,000,
Move: 012,020,000,
Move: 013,021,000,

Why does the realloc behave that way?

Solution:

Remember that realloc (just as malloc) requires the size in bytes, not number of "elements". –

Try this.

Code:

        char** p= realloc(move_info->moves, 2*(move_info->array_size)*sizeof(*p) );
        if(!p){
            return 0;
        } else {
            move_info->moves = p;
            move_info->array_size = 2*(move_info->array_size);
        }

Yes, as you said, realloc counts bytes not objects.
So you need the *sizeof thing in there as well.