Macro representing maximum value for uint64_t

c++ uint64
Subway picture Subway · Apr 30, 2013 · Viewed 40.1k times · Source

I'm seeking for a macro representing the maximum value of uint64_t as UINT_MAX is for unsigned int. i.e. I need this value to guaranteed to be (1<<64)-1.

I tried to use UINT64_MAX, but compiling with g++ results in: 

'UINT64_MAX' was not declared in this scope

It's worth to mention that I have this line #define __STDC_LIMIT_MACROS in the code before using UINT64_MAX.

I was surprised to not find helpful information around the web about it.

Answer

pmr picture pmr · Apr 30, 2013

Using the cstdint header portably can be quite a challenge (it is missing from some MSVC implementations). At the same time numeric_limits::max() can be hard to use without constexpr and it is not actually required to work with uint64_t. If you don't care about those things too much, std::numeric_limits<uint64_t>::max() will most likely do the trick.

Boost.Integer has an implementation of cstdint and comes with an extra traits class to get a constant maximal value. A compliant implementation of cstdint should also provide the macro UINT64_MAX, but I'm not sure about boost.

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