Solidity uses state-reverting exceptions to handle errors. Such an exception will undo all changes made to the state in the current call(and all its sub-calls) and also flag an error to the caller. The convenience function
require can be used to check for conditions and throw an exception if the condition is not met.
assert function should only be used to test for internal errors, and to check invariants.
require function should be used to ensure valid conditions, such as inputs, or contract state variables are met, or to validate return values from calls to external contracts.
If used properly, analysis tools can evaluate your contract to identify the conditions and function calls which will reach a failing
assert. Properly functioning code should never reach a failing assert statement. If this happens there is a bug in your contract which you should fix.
There are two ways to trigger exceptions:
revertfunction can be used to flag an error and revert the current call. In the future, it might be possible to also include details about error in a call to
throwkeyword can also be used as an alternative to
From 0.4.13, the
When exceptions happen in a sub-call, they ‘bubble up’ automatically. Exceptions to this rule are
send and the low-level functions
callcode – those return
false in case of an exception instead of ‘bubble up’.
callcodereturn false when exceptions occur.
Catch exceptions is not yet possible.