From eosio.cdt v1.6 onwards
You have to #include <eosio/system.hpp> and then you can use:

eosio::current_time_point
eosio::current_block_time
to cast from time_point to uint32_t u can use like:
eosio::current_time_point().sec_since_epoch();

参考

https://github.com/EOSIO/eosio.cdt/issues/470