stxxl::for_each

Author

Roman Dementiev (2006)

The semantics of the algorithm is equivalent to the STL std::for_each.

Prototype

template < typename ExtIterator, typename UnaryFunction >
UnaryFunction for_each ( ExtIterator   first,
                         ExtIterator   last,
                         UnaryFunction functor,
                         int_type       nbuffers
                       )

Description

stxxl::for_each applies the function object functor to each element in the range [first, last); functor's return value, if any, is ignored. Applications are performed in forward order, i.e. from first to last. stxxl::for_each returns the function object after it has been applied to each element. To overlap I/O and computation nbuffers used (a value at least D is recommended). The size of the buffers is derived from the container that is pointed by the iterators.

Remarks

The implementation exploits STXXL buffered streams (computation and I/O overlapped).

Parameters

begin	object of model of ext_random_access_iterator concept
end	object of model of ext_random_access_iterator concept
functor	function object of model of std::UnaryFunction concept
nbuffers	number of buffers (blocks) for internal use (should be at least 2*D )

Returns

function object functor after it has been applied to the each element of the given range

Warning

nested stxxl::for_each are not supported

Requirements on types

• ExtIterator is a model of External Random Access Iterator.
• UnaryFunction is a model of STL Unary Function.
• UnaryFunction does not apply any non-constant operations through its argument.
• ExtIterator's value type is convertible to UnaryFunction's argument type.

Preconditions

[first, last) is a valid range.

Complexity

• Internal work is linear.
• External work: close to I/Os (read-only).

Example

template<class T>
struct print : public unary_function<T, void>
{
    print(ostream& out) : os(out), count(0) {}
    void operator() (T x) { os << x << ' '; ++count; }
    ostream& os;
    int count;
};
typedef stxxl::VECTOR_GENERATOR<int>::result vector_type;
int main()
{
    vector_type A(N);
    // fill A with some values
    // ...

    print<int> P = stxxl::for_each(A.begin(), A.end(), print<int>(cout));
    cout << endl << P.count << " objects printed." << endl;
}