currentMSecsSinceEpoch using specific DateTime

[gab74]

Good morning,
i see on QT Docs that :

qint64 QDateTime::currentMSecsSinceEpoch () [static]
Returns the number of milliseconds since 1970-01-01T00:00:00 Universal Coordinated Time

qint64 QDateTime::currentMSecsSinceEpoch () [static]
Returns the number of milliseconds since 1970-01-01T00:00:00 Universal Coordinated Time

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I want to know the milliseconds since 1970-01-01T00:00:00 Universal Coordinated Time for a specific Date Time.

How can i reach it ?

Thanks
Gabriele