Transform performs an operation on objects; there are two versions of transform, one of which uses a single range of Input Iterators and one of which uses two ranges of Input Iterators.

The first version of transform performs the operation op(*i) for each iterator i in the range [first, last) , and assigns the result of that operation to *o, where o is the corresponding output iterator. That is, for each n such that 0 <= n < last – first, it performs the assignment *(result + n) = op(*(first + n)). The return value is result + (last – first).

The second version of transform is very similar, except that it uses a Binary Function instead of a Unary Function: it performs the operation op(*i1, *i2) for each iterator i1 in the range [first1, last1) and assigns the result to *o, where i2 is the corresponding iterator in the second input range and where o is the corresponding output iterator. That is, for each n such that 0 <= n < last1 – first1, it performs the assignment *(result + n) = op(*(first1 + n), *(first2 + n). The return value is result + (last1 – first1).

Note that transform may be used to modify a sequence "in place": it is permissible for the iterators first and result to be the same. [1]