如何使用fmt在Go中打印出常量uint64？

Question

I tried:

fmt.Printf("%d", math.MaxUint64)

but I got the following error message:

constant 18446744073709551615 overflows int

How can I fix this? Thanks!

Answer 1

math.MaxUint64 is a constant, not an int64. Try instead:

fmt.Printf("%d", uint64(num))

The issue here is that the constant is untyped. The constant will assume a type depending on the context in which it is used. In this case, it is being used as an interface{} so the compiler has no way of knowing what concrete type you want to use. For integer constants, it defaults to int. Since your constant overflows an int, this is a compile time error. By passing uint64(num), you are informing the compiler you want the value treated as a uint64.

Note that this particular constant will only fit in a uint64 and sometimes a uint. It is even bigger than a standard int64.