What is 1LL or 2LL in C and C++?

问题

I was looking at some of the solutions in Google Code Jam and some people used this things that I had never seen before. For example,

2LL*r+1LL

What does 2LL and 1LL mean?

Their includes look like this:

#include <math.h>
#include <algorithm>
#define _USE_MATH_DEFINES

or

#include <cmath>

回答1:

The LL makes the integer literal of type long long.

So 2LL, is a 2 of type long long.

Without the LL, the literal would only be of type int.

This matters when you're doing stuff like this:

1   << 40
1LL << 40

With just the literal 1, (assuming int to be 32-bits, you shift beyond the size of the integer type -> undefined behavior). With 1LL, you set the type to long long before hand and now it will properly return 2^40.

来源：https://stackoverflow.com/questions/16248221/what-is-1ll-or-2ll-in-c-and-c