struct buffer
{
	int begin, end, size;
	char *buf;
};
typedef struct buffer buffer;
buffer* create_buffer(int size)
{
	buffer *b = (buffer *)calloc(1, sizeof(*b));
	b->begin = b->end = 0;
	b->size = size;
	b->buf = (char *)calloc(size, sizeof(b->buf[0]));
	return b;
}
void write_buffer(buffer *b, void *data, int size)
{
	char *d = (char *)data;
	for (int i = 0; i < size && b->begin != (b->end + 1) % b->size; ++i)
	{
		b->buf[b->end] = d[i];
		b->end = (b->end + 1) % b->size;
	}
}
void read_buffer(buffer *b, void *data, int size)
{
	char *d = (char *)data;
	for (int i = 0; i < size && b->begin != b->end; ++i)
	{
		d[i] = b->buf[b->begin];
		b->begin = (b->begin + 1) % b->size;
	}
}
int main(void)
{
	buffer* b = create_buffer(10);
	char s[] = "asdasd";
	char s2[] = "qweqwerty";
	write_buffer(b, s, sizeof(s));
	write_buffer(b, s2, sizeof(s2));
	char s3[100];
	read_buffer(b, s3, sizeof(s3));
	for (int i = 0; i < 10; ++i)
		printf("%c", s3[i]);
	return 0;
}