# set_diff(3C++)

**set_diff --
treating arrays as sets, take the set difference
**

## Synopsis

template <class **T**>
**T*** set_diff(
const **T*** b1,
const **T*** e1,
const **T*** b2,
const **T*** e2,
**T*** b3
);
template <class **T**>
**T*** set_diff_r(
int (*rel)(const **T***,const **T***),
const **T*** b1,
const **T*** e1,
const **T*** b2,
const **T*** e2,
**T*** b3
);

## Assumptions

(1) For the plain version, **T::operator<** defines a total
ordering relation on **T** and both input arrays are sorted w.r.t.
that relation.

(2) For the relational version, **rel** defines a total ordering
relation on **T** and both input arrays are sorted w.r.t. that relation.

(3) Neither of the input arrays has repetitions.

(4) The output array does not overlap either of the two input arrays.

(5) The output array has enough cells to hold the result.

(6) **T** has **operator=**.

## Description

These functions put elements from two sorted arrays with no repetitions into
a new sorted array with no repetitions such that every element
which is in the first
array but not in the second will be placed in the new array.
They return a pointer
to the cell just beyond the last element of the new array.

template <class T>
T* set_diff(
const T* b1,
const T* e1,
const T* b2,
const T* e2,
T* b3
);

Uses **T::operator<** for comparing elements.

template <class T>
T* set_diff_r(
int (*rel)(const T*,const T*),
const T* b1,
const T* e1,
const T* b2,
const T* e2,
T* b3
);

Uses **rel** for comparing elements.

## Complexity

If *N* and *M* are the
sizes of the arrays, then complexity is *O(N+M)*.
At most
*N+M-1* comparisons and *N*
assignments are done.

## Notes

All functions whose names begin with **set_** treat arrays
as sets (they share assumptions 1-3).
These all have linear time complexity, which
may unacceptable for large sets.
As an alternative, consider using **Set(3C++)**
or **Bits(3C++)** (if **T** is **int**).

Because a Block (see **Block(3C++)**) can always be used wherever
an array is called for, Array Algorithms can also be used with Blocks.
In fact,
these two components were actually designed to be used together.

## References

**Array_alg**(3C++),
**Bits**(3C++),
**Block**(3C++),
**Set**(3C++),
**set_inter**(3C++),
**set_insert**(3C++),
**set_remove**(3C++),
**set_union**(3C++),
**set_sdiff**(3C++)

*
© 2004 The SCO Group, Inc. All rights reserved.
*

UnixWare 7 Release 7.1.4 - 25 April 2004