#include<stdlib.h>
#include<stdio.h>
#include<string.h>
#include<unistd.h>

#define STRING_INIT {0, 0, 0}

struct string {
	char *data;
	size_t len;
	size_t space;
};

void add(struct string* s, char *addition){
	size_t space_left = s->space - s->len;
	size_t addition_len = strlen(addition);
	if(space_left < addition_len){
		s->data = realloc(s->data, s->len + addition_len);
		s->space = s->len + addition_len;
	}
	strcpy(s->data + s->len, addition);
	s->len += addition_len;
}

void reserve(struct string* s, size_t capacity){
	if(capacity < s->len)
		return;
	s->data = realloc(s->data, capacity);
	s->space = capacity;
}

void set_length_by_null(struct string* s){
	s->len = strlen(s->data);
}

int main(){

	struct string animals = STRING_INIT;
	reserve(&animals, 100);
	gethostname(animals.data, animals.space);
	set_length_by_null(&animals);
	
	add(&animals, " ");
	add(&animals, "Zebra ");
	add(&animals, "Cheetah ");
	add(&animals, "Sloth ");
	
	printf("Animals:  %s\n", animals.data);
	
	return 0;
}