HP Integrity NonStop H-Series - Manual (Page 157)

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©Copyright 1996 Rogue Wave Software
In-Place Transformations
Obtaining the Source
The next category of algorithms in the standard library that we examine are those used to modify
and transform sequences without moving them from their original storage locations. A few of these
routines, such as replace(), include a copy version as well as the original in-place transformation
algorithms. For the others, should it be necessary to preserve the original, a copy of the sequence
should be created before the transformations are applied. For example, the following illustrates how
one can place the reversal of one vector into another newly allocated vector.
vector newVec(aVec.size());
copy (aVec.begin(), aVec.end(), newVec.begin()); // first copy
reverse (newVec.begin(), newVec.end()); // then reverse
Many of the algorithms described as sequence generating operations, such as transform()
(
Transform One or Two Sequences ), or partial_sum(), can also be used to modify a value in place
by simply using the same iterator as both input and output specification.
Reverse Elements in a Sequence
The algorithm reverse() reverses the elements in a sequence, so that the last element becomes the
new first, and the first element the new last. The arguments are assumed to be bidirectional iterators,
and no value is returned.
void reverse (BidirectionalIterator first,
BidirectionalIterator last);
The example program illustrates two uses of this algorithm. In the first, an array of characters
values is reversed. The algorithm reverse() can also be used with list values, as shown in the second
example. In this example, a list is initialized with the values 2 to 11 in increasing order. (This is
accomplished using the iotaGen function object introduced in
Chapter 3: Functions Objects ). The list
is then reversed, which results in the list holding the values 11 to 2 in decreasing order. Note,
however, that the list data structure also provides its own reverse() member function.
void reverse_example ()
// illustrate the use of the reverse algorithm
{
// example 1, reversing a string
char * text = "Rats live on no evil star";