C / C++ / MFC

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

struct thing1
{
	int n;
	char* word;
	
};

struct thing2
{
	int n;
	char* word;
	struct thing1 *node1;
};

struct response
{
	int n;
	struct thing2 *node2;
};

///declarations
//with malloc
int getDynamicResponse(struct response* res);
//without malloc
int getResponse(struct response* res);
//by ref
int getRefResponse(struct response* res);

//get structs
struct thing1 getThing1();
struct thing2 getThing2();
//by ref
void refThing1(struct thing1* out);
void refThing2(struct thing2* out);
//print
void showThing1(struct thing1 *t1);
void showThing2(struct thing2 *t2);
void showResponse(struct response *res);

///implementation
//get structs
struct thing1 getThing1()
{
	struct thing1 t1;
	t1.n = 1;
	t1.word = "thing1";
	return t1;
}

struct thing2 getThing2()
{
	struct thing2 t2;
	t2.n = 2;
	t2.word = "thing2";
	return t2;
}

//by ref
void refThing1(struct thing1* out)
{
	struct thing1 t1;
	t1.n = 3;
	t1.word = "refthing3";
	*out = t1;
}

void refThing2(struct thing2* out)
{
	struct thing2 t2;
	t2.n = 4;
	t2.word = "refthing4";
	*out = t2;
}

//print
void showThing1(struct thing1 *t1)
{
	printf("thing1\n");
	if(t1)
	{
		int i = t1->n;
		if(i) printf("n=%d\n", i);
		if(t1->word) printf("word=%s\n", t1->word);
	}
	else printf("Thing1 NULL");
}

void showThing2(struct thing2 *t2)
{
	printf("thing2\n");
	if(t2)
	{
		printf("n=%d\n", t2->n);
		if(t2->word) printf("word=%s\n", t2->word);
		if(t2->node1) showThing1(t2->node1);
	}
	else printf("Thing2 NULL");
}

void showResponse(struct response *res)
{
	if(res)
	{
		printf("response\n");
		printf("n=%d\n", res->n);
		if(res->node2) showThing2(res->node2);
	}
	else printf("Response NULL");
	
}

//with malloc
int getDynamicResponse(struct response* res)
{
	printf("\nwith malloc\n");
	printf("n=%d\n", res->n);
	struct response *tmp;
	tmp = (struct response*)malloc(sizeof(struct response));
	tmp->n = 12345;
	tmp->node2 = (struct thing2*)malloc(sizeof(struct thing2));
	tmp->node2->n = 2468;
	tmp->node2->word = "malloc1";
	tmp->node2->node1 = (struct thing1*)malloc(sizeof(struct thing1));
	tmp->node2->node1->n = 987;
	tmp->node2->node1->word = "malloc2";
	
	*res = *tmp;
	showResponse(res);
	printf("***************************\n");
	return 0;
}
//by ref
int getRefResponse(struct response* res)
{
	printf("\nby pointer ref\n");
	printf("n=%d\n", res->n);
	struct response out, *pout;
	res->n = 888;
	struct thing2 t2;
	struct thing1 t1;
	refThing2(&t2);	
	refThing1(&t1);	
	struct thing1 *p1 = &t1;
	struct thing2 *p2 = &t2;
	
	//link nodes
	pout = &out;
	pout->node2 = p2;
	pout->node2->node1 = p1;
	
	*res = out;
	showResponse(res);
	printf("***************************\n");
	return 0;
}

//without malloc
int getResponse(struct response* res)
{
	printf("\nlocal stack\n");
	printf("n=%d\n", res->n);
	struct response out, *pout;
	res->n = 99;
	struct thing2 tmp2 = getThing2();
	struct thing1 tmp1 = getThing1();
	struct thing1 *p1 = &tmp1;
	struct thing2 *p2 = &tmp2;
	//link nodes
	pout = &out;
	pout->node2 = p2;
	pout->node2->node1 = p1;
	
	*res = out;
	showResponse(res);
	printf("***************************\n");
	return 0;
}

int main(int argc, char **argv)
{
	printf("structs\n");
	struct response r1, r2, r3;
	r1.n = 51;
	r2.n = 52;
	r3.n = 53;
	getResponse(&r1);
	//error: local stack garbage	showResponse(&r1);
	printf("=====================\n");
	getRefResponse(&r2);
	showResponse(&r2);
	printf("=====================\n");
	getDynamicResponse(&r3);
	showResponse(&r3);
	printf("=====================\n");
	getchar();
	return 0;
}