Dealing with overflow in chrono

Is there a way to easily automate this checking in modern C++, at least for debug builds?

Yes.

The <chrono> durations (and time_points) can use class types for the underlying representation as opposed to integral (or floating point) types. For example they can use a "safe int" type that turns overflow into a noisy run-time error.

One free, open-source, header-only example of such a class is the bbi integer library.1 This library can be used to easily define your own custom chrono types that will terminate on overflow.

For example:

#include "bbi.h" #include <chrono> #include <iostream> namespace mychrono { using namespace bbi::term; using nanoseconds = std::chrono::duration<i64, std::nano>; using microseconds = std::chrono::duration<i64, std::micro>; using milliseconds = std::chrono::duration<i64, std::milli>; using seconds = std::chrono::duration<i64>; using minutes = std::chrono::duration<i32, std::ratio<60>>; using hours = std::chrono::duration<i32, std::ratio<3'600>>; using days = std::chrono::duration<i32, std::ratio<86'400>>; using weeks = std::chrono::duration<i32, std::ratio<604'800>>; using months = std::chrono::duration<i32, std::ratio<2'629'746>>; using years = std::chrono::duration<i32, std::ratio<31'556'952>>; } // namespace mychrono int main() { using namespace mychrono; years y{300}; nanoseconds x{300}; std::cout << (y > x) << '\n'; }

This requires C++20 or later, and on recent versions of MSVC, gcc and clang, will output the message:

Z<Signed, 64, Terminate>{300) * Z<Signed, 64, Terminate>{31556952000000000) overflowed

and then call std::terminate.

Working demo for all three major platforms.

The only changes to the code are:

#include "bbi.h" Type aliases for the chrono types under your own namespace Change using namespace std::chrono to using namespace mychrono (or manage the namespace change however you prefer).

Once you have debugged your code and want to return to the full efficiency of a release build, simply change:

using namespace bbi::term;

to:

using namespace bbi::raw;

This change redefines your custom chrono types to use built in signed integers of the indicated bit width for their representation.

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If you would like to throw an exception on overflow instead of call std::terminate, then change:

using namespace bbi::term;

to:

using namespace bbi::thrw;

Then on overflow a std::overflow_error will be thrown with a what() message identical to the one printed out previously with terminate().

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To experiment with saturated arithmetic change:

using namespace bbi::term;

to:

using namespace bbi::sat;

Now this program outputs the correct answer:

1

300 years is greater than 300ns.

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Another way to use this library to get the correct answer instead of overflow is to increase the range of nanoseconds to +/- far beyond the age of the universe. This can be done by having nanoseconds represented by a signed 128 bit type, instead of a 64 bit type. Change:

using nanoseconds = std::chrono::duration<i64, std::nano>;

to:

using nanoseconds = std::chrono::duration<i128, std::nano>;

Now this program outputs the correct answer:

1

300 years is greater than 300ns.

You can no longer have a zero overhead release build with this setting as there is no portable 128 bit type (until we get a portable _BitInt(128)), but you can remove the overflow checks by changing:

using namespace bbi::term;

to:

using namespace bbi::wrap;

Working C++20 demo.

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1 I am the main author of bbi. I am not seeking any financial benefit from this library. I consider helping people with C++ in general, and chrono in particular a hobby of mine.