int t;
t=(int)(ptr+1)-(int)(ptr);

#include <stdlib.h>
/* struct example change it for each struct */
typedef struct
{
    char a[10];
    int  b;
} mystruct_t;

size_t dbl_size=0;
size_t int_size=0;
/* ISO C has CHAR_BIT fixed to eight bits.  If it's an 8 bit per byte machine, char = 1 byte */
size_t char_size=0; 
size_t mystruct_t_size=0;

unsigned long diff(const void *a, const void *b)
{
	unsigned long diff=((unsigned char *)b - (unsigned char *)a);
	return diff;
}

void set_sizes(void)
{
	unsigned char *p=NULL;
	int arr1[2];
	double arr2[2];
	mystruct_t arr3[2];
	char arr4[2];
	dbl_size=diff(&arr2[0],&arr2[1]);
	int_size=diff(&arr1[0],&arr1[1]);
	mystruct_t_size=diff(&arr3[0],&arr3[1]);
	char_size=diff(&arr4[0],&arr4[1]);
}

int main()
{
	set_sizes();
	printf("dbl_size=        %u\n",dbl_size);
	printf("int_size=      	 %u\n",int_size);     
	printf("char_size=       %u\n",char_size);
	printf("mystruct_t_size= %u\n",mystruct_t_size);
	return 0;                      
}

#include <stdio.h>

int main(int argc, char **argv) {

        int i;
        int j = (int)(&i+1)-(int)&i;
        printf ("(int)(&i+1)-(int)&i= %d\n", j);
        printf ("sizeof(i)= %d\n", sizeof(i));

        return 0;
}

(int)(&i+1)-(int)&i= 4
sizeof(i)= 4