What does 512L mean? (or probably any number followed by capital L)
example:
uint sec
and then some code with the expression:
sec * 512L
(taken out of the XV6 code - mkfs.c)
L stands for long.
This creates a literal of type long.
l would also work, but it looks like 1, so it should be avoided.
来源：https://stackoverflow.com/questions/17332477/number-followed-by-capital-l