Mismatch finds the first position where the two ranges [first1, last1) and [first2, first2 + (last1 – first1)) differ. The two versions of mismatch use different tests for whether elements differ.

The first version of mismatch finds the first iterator i in [first1, last1) such that *i != *(first2 + (i – first1)). The return value is a pair whose first element is i and whose second element is *(first2 + (i – first1)). If no such iterator i exists, the return value is a pair whose first element is last1 and whose second element is *(first2 + (last1 – first1)).

The second version of mismatch finds the first iterator i in [first1, last1) such that binary_pred(*i, *(first2 + (i – first1)) is false. The return value is a pair whose first element is i and whose second element is *(first2 + (i – first1)). If no such iterator i exists, the return value is a pair whose first element is last1 and whose second element is *(first2 + (last1 – first1)).