Thread: Dynamic array help

Originally Posted by laserlight

Try calling the add() function more than once in your main() function. You have a problem in that the array parameter is just a pointer, so this merely changes the local copy of the pointer:

Code:

array = (student*)realloc(array, ((*array_size) * sizeof(student)));

You should declare array to be a pointer to a student*. (Maybe you should also rename it to students.)

sorry but I don't think I'm quite following, you mean that array should be a double pointer??

Originally Posted by Perogy

sorry but I don't think I'm quite following, you mean that array should be a double pointer??

Yes, a student**. But not in main(), only in the add() function, so when you call the function from main the first argument will be &array.

ahhh ok I see what you mean, just so we can change the original it needs to be passed in as an address. I did that and now it seems to work perfectly for the first time I use add but if I use it again it segfaults. This is my new Student.

Code:

#include <stdlib.h>
#include <stdio.h>
#include "student.h"

void add(student **array, student item, int *number_of_elements, int *array_size)
{
	if (*number_of_elements == *array_size) /*resize array*/
	{
		if (*array_size == 0)
		{
			*array_size = 1;
		}
		else
		{
			*array_size = *array_size * 2;
		}
		*array = (student*)realloc(*array, ((*array_size) * sizeof(student)));
		
		if (*array == 0)
		{
			printf("no space for memory");
			exit(1);
		}
	}
	*array[*number_of_elements] = item;
	(*number_of_elements)++;
}