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### 1410. Add a feature-detect macro for `monotonic_clock`

Section: 99 [time.clock.monotonic] Status: Resolved Submitter: BSI Opened: 2010-08-25 Last modified: 2016-01-28

Priority: Not Prioritized

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Duplicate of: 1411

Discussion:

Addresses GB-107, DE-20

4.1 [intro.compliance] p.9 states that which conditionally supported constructs are available should be provided in the documentation for the implementation. This doesn't help programmers trying to write portable code, as they must then rely on implementation-specific means to determine the availability of such constructs. In particular, the presence or absence of `std::chrono::monotonic_clock` may require different code paths to be selected. This is the only conditionally-supported library facility, and differs from the conditionally-supported language facilities in that it has standard-defined semantics rather than implementation-defined semantics.

[ Resolution proposed in ballot comment: ]

Provide feature test macro for determining the presence of `std::chrono::monotonic_clock`. Add `_STDCPP_HAS_MONOTONIC_CLOCK` to the `<chrono>` header, which is defined if `monotonic_clock` is present, and not defined if it is not present.

[ 2010-11-01 Daniel comments: ]

> Paper n3128 addresses this issue by replacing `monotonic_clock` with `steady_clock`, which is not conditionally supported, so there is no need to detect it.

Proposed resolution:

This is resolved by n3191.