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In Solidity, people use a SafeMath library to prevent overflow/underflow attack. So, I wonder what's the best way to prevent overflow/underflow attack for EOS contract. Is there an easy-to-use SafeMath library available?

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EOS uses C ++, and C ++ assert can be used to check for overflow or underflow.

ex) assert( quantity + a.quantity >= a.quantity,"integer overflow adding token balance" );

See the link below for this.

https://steemit.com/eos/@dan/eos-example-exchange-contract-and-benefits-of-c

Also, eosio provides eosio_assert to enable various assertions.

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    That check only works for unsigned types. Optimizing compilers often strip out that check on signed types since ISO C and ISO C++ make signed overflow undefined behavior. Asset uses signed.
    – Todd Fleming
    Commented Jun 24, 2018 at 20:31
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    AFAIK assert() is a macro and not active in the production compiled code, instead it is preprocessed out. So this would not prevent attack.
    – Mikko Ohtamaa
    Commented Jun 25, 2018 at 9:22

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