为什么这段代码会报错?

#include<bits/stdc++.h>
using namespace std;
bitset<1000010> dp;
int main(){
	printf("%d",dp[1]);
	return 0;
}
//[Error] cannot pass objects of non-trivially-copyable type 'class std::bitset<1000010ull>::reference' through '...'

这样却不会报错?

#include<bits/stdc++.h>
using namespace std;
bitset<1000010> dp;
int main(){
	cout<<dp[1]<<endl;
	return 0;
}