SGI extensions to the library in
libstdc++-v3
This page describes the extensions that SGI made to their version of the
STL subset of the Standard C++ Library.  For a time we
../faq/index.html#5_3
tracked and imported changes and updates
from most of the SGI STL
, up through their (apparently) final release.
Their extensions were mostly preserved.
They are listed according to the chapters of the library that they
extend (see
../documentation.html#3
the chapter-specific notes
for a description).  Not every chapter may have extensions, and the
extensions may come and go.  Also, this page is incomplete because the
author is pressed for time.  Check back often; the latest change was on
$Date: 2003/04/16 17:02:47 $ (UTC).
Descriptions range from the scanty to the verbose.  You should also check
the
../documentation.html#4
generated documentation
for notes
and comments, especially for entries marked with '*'.  For more complete
doumentation, see the SGI website.  For
really
complete
documentation, buy a copy of Matt Austern's book.  *grin*
Back to the
howto.html
libstdc++-v3 extensions
.
Chapter 20
The <functional> header contains many additional functors and
helper functions, extending section 20.3.  They are implemented in the
file stl_function.h:
identity_element
for addition and multiplication. *
The functor
identity
, whose
operator()
returns the argument unchanged. *
Composition functors
unary_function
and
binary_function
, and their helpers
compose1
and
compose2
. *
select1st
and
select2nd
, to strip pairs. *
project1st
and
project2nd
. *
A set of functors/functions which always return the same result.  They
are
constant_void_fun
,
constant_binary_fun
,
constant_unary_fun
,
constant0
,
constant1
, and
constant2
. *
The class
subtractive_rng
. *
mem_fun adaptor helpers
mem_fun1
and
mem_fun1_ref
are provided for backwards compatibility.
20.4.1 can use several different allocators; they are described on the
main extensions page.
20.4.3 is extended with a special version of
get_temporary_buffer
taking a second argument.  The argument
is a pointer, which is ignored, but can be used to specify the template
type (instead of using explicit function template arguments like the
standard version does).  That is, in addition to
get_temporary_buffer<int>(5);
you can also use
get_temporary_buffer(5, (int*)0);
A class
temporary_buffer
is given in stl_tempbuf.h. *
The specialized algorithms of section 20.4.4 are extended with
uninitialized_copy_n
. *
Return
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or
http://gcc.gnu.org/libstdc++/
to the homepage
.
Chapter 23
A few extensions and nods to backwards-compatibility have been made with
containers.  Those dealing with older SGI-style allocators are dealt with
elsewhere.  The remaining ones all deal with bits:
The old pre-standard
bit_vector
class is present for
backwards compatibility.  It is simply a typedef for the
vector<bool>
specialization.
The
bitset
class has a number of extensions, described in the
rest of this item.  First, we'll mention that this implementation of
bitset<N>
is specialized for cases where N number of
bits will fit into a single word of storage.  If your choice of N is
within that range (<=32 on i686-pc-linux-gnu, for example), then all
of the operations will be faster.
There are
versions of single-bit test, set, reset, and flip member functions which
do no range-checking.  If we call them member functions of an instantiation
of "bitset<N>," then their names and signatures are:
bitset<N>&   _Unchecked_set   (size_t pos);
bitset<N>&   _Unchecked_set   (size_t pos, int val);
bitset<N>&   _Unchecked_reset (size_t pos);
bitset<N>&   _Unchecked_flip  (size_t pos);
bool         _Unchecked_test  (size_t pos);
Note that these may in fact be removed in the future, although we have
no present plans to do so (and there doesn't seem to be any immediate
reason to).
The semantics of member function
operator[]
are not specified
in the C++ standard.  A long-standing defect report calls for sensible
obvious semantics, which are already implemented here:
op[]
on a const bitset returns a bool, and for a non-const bitset returns a
reference
(a nested type).  However, this implementation does
no range-checking on the index argument, which is in keeping with other
containers'
op[]
requirements.  The defect report's proposed
resolution calls for range-checking to be done.  We'll just wait and see...
Finally, two additional searching functions have been added.  They return
the index of the first "on" bit, and the index of the first
"on" bit that is after
prev
, respectively:
size_t _Find_first() const;
size_t _Find_next (size_t prev) const;
The same caveat given for the _Unchecked_* functions applies here also.
Return
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or
http://gcc.gnu.org/libstdc++/
to the homepage
.
Chapter 24
24.3.2 describes
struct iterator
, which didn't exist in the
original HP STL implementation (the language wasn't rich enough at the
time).  For backwards compatibility, base classes are provided which
declare the same nested typedefs:
input_iterator
output_iterator
forward_iterator
bidirectional_iterator
random_access_iterator
24.3.4 describes iterator operation
distance
, which takes
two iterators and returns a result.  It is extended by another signature
which takes two iterators and a reference to a result.  The result is
modified, and the function returns nothing.
Return
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or
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.
Chapter 25
25.1.6 (count, count_if) is extended with two more versions of count
and count_if.  The standard versions return their results.  The
additional signatures return void, but take a final parameter by
reference to which they assign their results, e.g.,
void count (first, last, value, n);
25.2 (mutating algorithms) is extended with two families of signatures,
random_sample and random_sample_n.
25.2.1 (copy) is extended with
copy_n (_InputIter first, _Size count, _OutputIter result);
which copies the first 'count' elements at 'first' into 'result'.
25.3 (sorting 'n' heaps 'n' stuff) is extended with some helper
predicates.  Look in the doxygen-generated pages for notes on these.
is_heap
tests whether or not a range is a heap.
is_sorted
tests whether or not a range is sorted in
nondescending order.
25.3.8 (lexigraphical_compare) is extended with
lexicographical_compare_3way(_InputIter1 first1, _InputIter1 last1,
_InputIter2 first2, _InputIter2 last2)
which does... what?
Return
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.
Chapter 26
26.4, the generalized numeric operations such as accumulate, are extended
with the following functions:
power (x, n);
power (x, n, moniod_operation);
Returns, in FORTRAN syntax, "x ** n" where n>=0.  In the
case of n == 0, returns the
#ch20
identity element
for the
monoid operation.  The two-argument signature uses multiplication (for
a true "power" implementation), but addition is supported as well.
The operation functor must be associative.
The
iota
function wins the award for Extension With the
Coolest Name.  It "assigns sequentially increasing values to a range.
That is, it assigns value to *first, value + 1 to *(first + 1) and so
on."  Quoted from SGI documentation.
void iota(_ForwardIter first, _ForwardIter last, _Tp value);
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.
See
../17_intro/license.html
license.html
for copying conditions.
Comments and suggestions are welcome, and may be sent to
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