stxxl::for_each_m (mutating)

Author

Roman Dementiev (2006)

stxxl::for_each_m is a mutating version of stxxl::for_each, i.e. the restriction that Unary Function functor can not apply only constant operations through its argument does not exist.

Prototype

template < typename ExtIterator, typename UnaryFunction >
UnaryFunction for_each_m ( ExtIterator   first,
                           ExtIterator   last,
                           UnaryFunction functor,
                           int nbuffers
                         )

Description

stxxl::for_each_m 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_m returns the function object after it has been applied to each element. To overlap I/O and computation nbuffers are used (a value at least 2D 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	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_m are not supported

Requirements on types

• ExtIterator is a model of External Random Access Iterator.
• UnaryFunction is a model of STL Unary Function.
• 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 and write).

Example

struct AddX
{
    int x;
    AddX(int x_): x(x_) {}
    void operator() (int & val)
    { val += x; }
};

typedef stxxl::VECTOR_GENERATOR<int>::result vector_type;
int main()
{
    vector_type A(N);
    // fill A with some values ...

    // Add 5 to each value in the vector
    stxxl::for_each_m(A.begin(), A.end(), AddX(5));
}