c++ - What happens if you specify an allocator where the value_types are different? -

c++ - What happens if you specify an allocator where the value_types are different? -

say declare std::vector<std::string, std::allocator<char>>. what's worse can happen? ran , didn't seem run memory errors.

it results in undefined behavior. allocator-aware containers vector standard specifies in table 99:

requires: allocator_type::value_type same x::value_type.

(note same row specifies allocator_type must be typedef template argument of container-specialization) , acccording [res.on.functions]/2:

in particular, effects undefined in next cases: […] — types used template arguments when instantiating template component, if operations on type not implement semantics of applicable requirements subclause (17.6.3.5, 23.2, 24.2, 26.2).

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