struct.c

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


int main(int argc, char const* argv[])
{
	struct _hoge {
		int  x;
		int y;
		int len;
#define HEADER_SIZE (long)&((struct _hoge *)NULL)->data
		char data[1];
	} *hoge;

	int len = 3;

	hoge = (struct _hoge *)malloc(len+1 + HEADER_SIZE);
	hoge->x = 1;
	hoge->y = 2;
	hoge->len = len;
	hoge->data[0] = 'a';
	hoge->data[1] = 'b';
	hoge->data[2] = 'c';
	hoge->data[3] = '\0';

	printf("%d %d %d %s\n",hoge->x,hoge->y,hoge->len,hoge->data);

	return 0;
}

/* 
 * result:
 * 1 2 3 abc
 */