---
name: "SGIextensions"
section: "3cxx"
platform: "linux"
package: "libstdc++-12-doc"
version: "12.4.0-5"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/SGIextensions/3cxx"
---

# SGIextensions(3cxx)

SGI

## NAME

SGIextensions - SGI

## SYNOPSIS

### Classes

class **\_\_gnu\_cxx::binary\_compose\< \_Operation1, \_Operation2, \_Operation3 \>**\
 An **SGI extension** .  struct **\_\_gnu\_cxx::constant\_binary\_fun\< \_Result, \_Arg1, \_Arg2 \>**\
 An **SGI extension** .  struct **\_\_gnu\_cxx::constant\_unary\_fun\< \_Result, \_Argument \>**\
 An **SGI extension** .  struct **\_\_gnu\_cxx::constant\_void\_fun\< \_Result \>**\
 An **SGI extension** .  class **\_\_gnu\_cxx::hash\_map\< \_Key, \_Tp, \_HashFn, \_EqualKey, \_Alloc \>**\
 class **\_\_gnu\_cxx::hash\_multimap\< \_Key, \_Tp, \_HashFn, \_EqualKey, \_Alloc \>**\
 class **\_\_gnu\_cxx::hash\_multiset\< \_Value, \_HashFcn, \_EqualKey, \_Alloc \>**\
 class **\_\_gnu\_cxx::hash\_set\< \_Value, \_HashFcn, \_EqualKey, \_Alloc \>**\
 struct **\_\_gnu\_cxx::project1st\< \_Arg1, \_Arg2 \>**\
 An **SGI extension** .  struct **\_\_gnu\_cxx::project2nd\< \_Arg1, \_Arg2 \>**\
 An **SGI extension** .  struct **\_\_gnu\_cxx::rb\_tree\< \_Key, \_Value, \_KeyOfValue, \_Compare, \_Alloc \>**\
 class **\_\_gnu\_cxx::rope\< \_CharT, \_Alloc \>**\
 struct **\_\_gnu\_cxx::select1st\< \_Pair \>**\
 An **SGI extension** .  struct **\_\_gnu\_cxx::select2nd\< \_Pair \>**\
 An **SGI extension** .  class **\_\_gnu\_cxx::slist\< \_Tp, \_Alloc \>**\
 class **\_\_gnu\_cxx::subtractive\_rng**\
 struct **\_\_gnu\_cxx::temporary\_buffer\< \_ForwardIterator, \_Tp \>**\
 class **\_\_gnu\_cxx::unary\_compose\< \_Operation1, \_Operation2 \>**\
 An **SGI extension** .

### Functions

template\<typename \_Tp \> const \_Tp & **\_\_gnu\_cxx::\_\_median** (const \_Tp &\_\_a, const \_Tp &\_\_b, const \_Tp &\_\_c)\
 Find the median of three values.  template\<typename \_Tp , typename \_Compare \> const \_Tp & **\_\_gnu\_cxx::\_\_median** (const \_Tp &\_\_a, const \_Tp &\_\_b, const \_Tp &\_\_c, \_Compare \_\_comp)\
 Find the median of three values using a predicate for comparison.  size\_t **std::bitset\< \_Nb \>::\_Find\_first** () const noexcept\
 Finds the index of the first 'on' bit.  size\_t **std::bitset\< \_Nb \>::\_Find\_next** (size\_t **\_\_prev**) const noexcept\
 Finds the index of the next 'on' bit after prev.  template\<class \_Operation1 , class \_Operation2 \> **unary\_compose**\< \_Operation1, \_Operation2 \> **\_\_gnu\_cxx::compose1** (const \_Operation1 &\_\_fn1, const \_Operation2 &\_\_fn2)\
 An **SGI extension** .  template\<class \_Operation1 , class \_Operation2 , class \_Operation3 \> **binary\_compose**\< \_Operation1, \_Operation2, \_Operation3 \> **\_\_gnu\_cxx::compose2** (const \_Operation1 &\_\_fn1, const \_Operation2 &\_\_fn2, const \_Operation3 &\_\_fn3)\
 An **SGI extension** .  template\<class \_Result \> **constant\_void\_fun**\< \_Result \> **\_\_gnu\_cxx::constant0** (const \_Result &\_\_val)\
 An **SGI extension** .  template\<class \_Result \> **constant\_unary\_fun**\< \_Result, \_Result \> **\_\_gnu\_cxx::constant1** (const \_Result &\_\_val)\
 An **SGI extension** .  template\<class \_Result \> **constant\_binary\_fun**\< \_Result, \_Result, \_Result \> **\_\_gnu\_cxx::constant2** (const \_Result &\_\_val)\
 An **SGI extension** .  template\<typename \_InputIterator , typename \_Size , typename \_OutputIterator \> **std::pair**\< \_InputIterator, \_OutputIterator \> **\_\_gnu\_cxx::copy\_n** (\_InputIterator \_\_first, \_Size \_\_count, \_OutputIterator \_\_result)\
 Copies the range \[first,first+count) into \[result,result+count).  template\<typename \_InputIterator , typename \_Distance \> void **\_\_gnu\_cxx::distance** (\_InputIterator \_\_first, \_InputIterator \_\_last, \_Distance &\_\_n)\
 template\<class \_Tp \> \_Tp **\_\_gnu\_cxx::identity\_element** (**std::multiplies**\< \_Tp \>)\
 An **SGI extension** .  template\<class \_Tp \> \_Tp **\_\_gnu\_cxx::identity\_element** (**std::plus**\< \_Tp \>)\
 An **SGI extension** .  template\<typename \_InputIterator1 , typename \_InputIterator2 \> int **\_\_gnu\_cxx::lexicographical\_compare\_3way** (\_InputIterator1 \_\_first1, \_InputIterator1 \_\_last1, \_InputIterator2 \_\_first2, \_InputIterator2 \_\_last2)\
 `memcmp` on steroids.  template\<typename \_Tp , typename \_Integer \> \_Tp **\_\_gnu\_cxx::power** (\_Tp \_\_x, \_Integer \_\_n)\
 template\<typename \_Tp , typename \_Integer , typename \_MonoidOperation \> \_Tp **\_\_gnu\_cxx::power** (\_Tp \_\_x, \_Integer \_\_n, \_MonoidOperation \_\_monoid\_op)\
 template\<typename \_InputIterator , typename \_RandomAccessIterator \> \_RandomAccessIterator **\_\_gnu\_cxx::random\_sample** (\_InputIterator \_\_first, \_InputIterator \_\_last, \_RandomAccessIterator \_\_out\_first, \_RandomAccessIterator \_\_out\_last)\
 template\<typename \_InputIterator , typename \_RandomAccessIterator , typename \_RandomNumberGenerator \> \_RandomAccessIterator **\_\_gnu\_cxx::random\_sample** (\_InputIterator \_\_first, \_InputIterator \_\_last, \_RandomAccessIterator \_\_out\_first, \_RandomAccessIterator \_\_out\_last, \_RandomNumberGenerator &\_\_rand)\
 template\<typename \_ForwardIterator , typename \_OutputIterator , typename \_Distance \> \_OutputIterator **\_\_gnu\_cxx::random\_sample\_n** (\_ForwardIterator \_\_first, \_ForwardIterator \_\_last, \_OutputIterator \_\_out, const \_Distance \_\_n)\
 template\<typename \_ForwardIterator , typename \_OutputIterator , typename \_Distance , typename \_RandomNumberGenerator \> \_OutputIterator **\_\_gnu\_cxx::random\_sample\_n** (\_ForwardIterator \_\_first, \_ForwardIterator \_\_last, \_OutputIterator \_\_out, const \_Distance \_\_n, \_RandomNumberGenerator &\_\_rand)\
 template\<typename \_InputIter , typename \_Size , typename \_ForwardIter \> **std::pair**\< \_InputIter, \_ForwardIter \> **\_\_gnu\_cxx::uninitialized\_copy\_n** (\_InputIter \_\_first, \_Size \_\_count, \_ForwardIter \_\_result)\
 Copies the range \[first,last) into result.  **bitset**\< **\_Nb** \> & **std::bitset\< \_Nb \>::\_Unchecked\_set** (size\_t **\_\_pos**) noexcept\
 **bitset**\< **\_Nb** \> & **std::bitset\< \_Nb \>::\_Unchecked\_set** (size\_t **\_\_pos**, int \_\_val) noexcept\
 **bitset**\< **\_Nb** \> & **std::bitset\< \_Nb \>::\_Unchecked\_reset** (size\_t **\_\_pos**) noexcept\
 **bitset**\< **\_Nb** \> & **std::bitset\< \_Nb \>::\_Unchecked\_flip** (size\_t **\_\_pos**) noexcept\
 constexpr bool **std::bitset\< \_Nb \>::\_Unchecked\_test** (size\_t **\_\_pos**) const noexcept\

## Detailed Description

Because libstdc++ based its implementation of the STL subsections of the library on the SGI 3.3 implementation, we inherited their extensions as well.

They are additionally documented in the `online documentation`, a copy of which is also shipped with the library source code (in .../docs/html/documentation.html). You can also read the documentation `on SGI's site`, which is still running even though the code is not maintained.

**NB** that the following notes are pulled from various comments all over the place, so they may seem stilted.

The `identity_element` functions are not part of the C++ standard; SGI provided them as an extension. Its argument is an operation, and its return value is the identity element for that operation. It is overloaded for addition and multiplication, and you can overload it for your own nefarious operations.

As an extension to the binders, SGI provided composition functors and wrapper functions to aid in their creation. The `unary_compose` functor is constructed from two functions/functors, `f` and `g`. Calling `operator()` with a single argument `x` returns `f(g(x))`. The function `compose1` takes the two functions and constructs a `unary_compose` variable for you.

`binary_compose` is constructed from three functors, `f`, `g1`, and `g2`. Its `operator()` returns `f`(g1(x),g2(x)). The function compose2 takes f, g1, and g2, and constructs the `binary_compose` instance for you. For example, if `f` returns an int, then

```
int answer = (compose2(f,g1,g2))(x);
```

 is equivalent to

```
int temp1 = g1(x);
int temp2 = g2(x);
int answer = f(temp1,temp2);
```

 But the first form is more compact, and can be passed around as a functor to other algorithms.

As an extension, SGI provided a functor called `identity`. When a functor is required but no operations are desired, this can be used as a pass-through. Its `operator()` returns its argument unchanged.

`select1st` and `select2nd` are extensions provided by SGI. Their `operator()s` take a `std::pair` as an argument, and return either the first member or the second member, respectively. They can be used (especially with the composition functors) to *strip* data from a sequence before performing the remainder of an algorithm.

The `operator()` of the `project1st` functor takes two arbitrary arguments and returns the first one, while `project2nd` returns the second one. They are extensions provided by SGI.

These three functors are each constructed from a single arbitrary variable/value. Later, their `operator()s` completely ignore any arguments passed, and return the stored value.

- •

  `constant_void_fun's` `operator()` takes no arguments

- •

  `constant_unary_fun's` `operator()` takes one argument (ignored)

- •

  `constant_binary_fun's` `operator()` takes two arguments (ignored)

The helper creator functions `constant0`, `constant1`, and `constant2` each take a *result* argument and construct variables of the appropriate functor type.

## Function Documentation

### template\<typename \_Tp \> const \_Tp & \_\_gnu\_cxx::\_\_median (const \_Tp & \_\_a, const \_Tp & \_\_b, const \_Tp & \_\_c)

Find the median of three values.

**Parameters**

*\_\_a* A value. \
 *\_\_b* A value. \
 *\_\_c* A value.

**Returns**

One of `a`, `b` or `c`.

If `{l`,m,n} is some convolution of `{a`,b,c} such that `l<=m<=n` then the value returned will be `m`. This is an SGI extension.

### template\<typename \_Tp , typename \_Compare \> const \_Tp & \_\_gnu\_cxx::\_\_median (const \_Tp & \_\_a, const \_Tp & \_\_b, const \_Tp & \_\_c, \_Compare \_\_comp)

Find the median of three values using a predicate for comparison.

**Parameters**

*\_\_a* A value. \
 *\_\_b* A value. \
 *\_\_c* A value. \
 *\_\_comp* A binary predicate.

**Returns**

One of `a`, `b` or `c`.

If `{l`,m,n} is some convolution of `{a`,b,c} such that `comp(l,m)` and `comp(m,n)` are both true then the value returned will be `m`. This is an SGI extension.

### template\<size\_t \_Nb\> size\_t std::bitset\< \_Nb \>::\_Find\_first () const` [inline]`, ` [noexcept]`

Finds the index of the first 'on' bit.

**Returns**

The index of the first bit set, or size() if not found.

**See also**

\_Find\_next

### template\<size\_t \_Nb\> size\_t std::bitset\< \_Nb \>::\_Find\_next (size\_t \_\_prev) const` [inline]`, ` [noexcept]`

Finds the index of the next 'on' bit after prev.

**Returns**

The index of the next bit set, or size() if not found.

**Parameters**

*\_\_prev* Where to start searching.

**See also**

\_Find\_first

### template\<size\_t \_Nb\> bitset\< \_Nb \> & std::bitset\< \_Nb \>::\_Unchecked\_flip (size\_t \_\_pos)` [inline]`, ` [noexcept]`

These versions of single-bit set, reset, flip, and test are extensions from the SGI version. They do no range checking.

### template\<size\_t \_Nb\> bitset\< \_Nb \> & std::bitset\< \_Nb \>::\_Unchecked\_reset (size\_t \_\_pos)` [inline]`, ` [noexcept]`

These versions of single-bit set, reset, flip, and test are extensions from the SGI version. They do no range checking.

### template\<size\_t \_Nb\> bitset\< \_Nb \> & std::bitset\< \_Nb \>::\_Unchecked\_set (size\_t \_\_pos)` [inline]`, ` [noexcept]`

These versions of single-bit set, reset, flip, and test are extensions from the SGI version. They do no range checking.

### template\<size\_t \_Nb\> bitset\< \_Nb \> & std::bitset\< \_Nb \>::\_Unchecked\_set (size\_t \_\_pos, int \_\_val)` [inline]`, ` [noexcept]`

These versions of single-bit set, reset, flip, and test are extensions from the SGI version. They do no range checking.

### template\<size\_t \_Nb\> constexpr bool std::bitset\< \_Nb \>::\_Unchecked\_test (size\_t \_\_pos) const` [inline]`, ` [constexpr]`, ` [noexcept]`

These versions of single-bit set, reset, flip, and test are extensions from the SGI version. They do no range checking.

### template\<class \_Operation1 , class \_Operation2 \> unary\_compose\< \_Operation1, \_Operation2 \> \_\_gnu\_cxx::compose1 (const \_Operation1 & \_\_fn1, const \_Operation2 & \_\_fn2)` [inline]`

An **SGI extension** .

### template\<class \_Operation1 , class \_Operation2 , class \_Operation3 \> binary\_compose\< \_Operation1, \_Operation2, \_Operation3 \> \_\_gnu\_cxx::compose2 (const \_Operation1 & \_\_fn1, const \_Operation2 & \_\_fn2, const \_Operation3 & \_\_fn3)` [inline]`

An **SGI extension** .

### template\<class \_Result \> constant\_void\_fun\< \_Result \> \_\_gnu\_cxx::constant0 (const \_Result & \_\_val)` [inline]`

An **SGI extension** .

### template\<class \_Result \> constant\_unary\_fun\< \_Result, \_Result \> \_\_gnu\_cxx::constant1 (const \_Result & \_\_val)` [inline]`

An **SGI extension** .

### template\<class \_Result \> constant\_binary\_fun\< \_Result, \_Result, \_Result \> \_\_gnu\_cxx::constant2 (const \_Result & \_\_val)` [inline]`

An **SGI extension** .

### template\<typename \_InputIterator , typename \_Size , typename \_OutputIterator \> std::pair\< \_InputIterator, \_OutputIterator \> \_\_gnu\_cxx::copy\_n (\_InputIterator \_\_first, \_Size \_\_count, \_OutputIterator \_\_result)` [inline]`

Copies the range \[first,first+count) into \[result,result+count).

**Parameters**

*\_\_first* An input iterator. \
 *\_\_count* The number of elements to copy. \
 *\_\_result* An output iterator.

**Returns**

A std::pair composed of first+count and result+count.

This is an SGI extension. This inline function will boil down to a call to `memmove` whenever possible. Failing that, if random access iterators are passed, then the loop count will be known (and therefore a candidate for compiler optimizations such as unrolling).

### template\<typename \_InputIterator , typename \_Distance \> void \_\_gnu\_cxx::distance (\_InputIterator \_\_first, \_InputIterator \_\_last, \_Distance & \_\_n)` [inline]`

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<class \_Tp \> \_Tp \_\_gnu\_cxx::identity\_element (std::multiplies\< \_Tp \>)` [inline]`

An **SGI extension** .

### template\<class \_Tp \> \_Tp \_\_gnu\_cxx::identity\_element (std::plus\< \_Tp \>)` [inline]`

An **SGI extension** .

### template\<typename \_InputIterator1 , typename \_InputIterator2 \> int \_\_gnu\_cxx::lexicographical\_compare\_3way (\_InputIterator1 \_\_first1, \_InputIterator1 \_\_last1, \_InputIterator2 \_\_first2, \_InputIterator2 \_\_last2)

`memcmp` on steroids.

**Parameters**

*\_\_first1* An input iterator. \
 *\_\_last1* An input iterator. \
 *\_\_first2* An input iterator. \
 *\_\_last2* An input iterator.

**Returns**

An int, as with `memcmp`.

The return value will be less than zero if the first range is *lexigraphically less than* the second, greater than zero if the second range is *lexigraphically less than* the first, and zero otherwise. This is an SGI extension.

### template\<typename \_Tp , typename \_Integer \> \_Tp \_\_gnu\_cxx::power (\_Tp \_\_x, \_Integer \_\_n)` [inline]`

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<typename \_Tp , typename \_Integer , typename \_MonoidOperation \> \_Tp \_\_gnu\_cxx::power (\_Tp \_\_x, \_Integer \_\_n, \_MonoidOperation \_\_monoid\_op)` [inline]`

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<typename \_InputIterator , typename \_RandomAccessIterator \> \_RandomAccessIterator \_\_gnu\_cxx::random\_sample (\_InputIterator \_\_first, \_InputIterator \_\_last, \_RandomAccessIterator \_\_out\_first, \_RandomAccessIterator \_\_out\_last)` [inline]`

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<typename \_InputIterator , typename \_RandomAccessIterator , typename \_RandomNumberGenerator \> \_RandomAccessIterator \_\_gnu\_cxx::random\_sample (\_InputIterator \_\_first, \_InputIterator \_\_last, \_RandomAccessIterator \_\_out\_first, \_RandomAccessIterator \_\_out\_last, \_RandomNumberGenerator & \_\_rand)` [inline]`

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<typename \_ForwardIterator , typename \_OutputIterator , typename \_Distance \> \_OutputIterator \_\_gnu\_cxx::random\_sample\_n (\_ForwardIterator \_\_first, \_ForwardIterator \_\_last, \_OutputIterator \_\_out, const \_Distance \_\_n)

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<typename \_ForwardIterator , typename \_OutputIterator , typename \_Distance , typename \_RandomNumberGenerator \> \_OutputIterator \_\_gnu\_cxx::random\_sample\_n (\_ForwardIterator \_\_first, \_ForwardIterator \_\_last, \_OutputIterator \_\_out, const \_Distance \_\_n, \_RandomNumberGenerator & \_\_rand)

This is an SGI extension.

**Todo**

Needs documentation! See http://gcc.gnu.org/onlinedocs/libstdc++/manual/documentation\_style.html

### template\<typename \_InputIter , typename \_Size , typename \_ForwardIter \> std::pair\< \_InputIter, \_ForwardIter \> \_\_gnu\_cxx::uninitialized\_copy\_n (\_InputIter \_\_first, \_Size \_\_count, \_ForwardIter \_\_result)` [inline]`

Copies the range \[first,last) into result.

**Parameters**

*\_\_first* An input iterator. \
 *\_\_count* Length \
 *\_\_result* An output iterator.

**Returns**

\_\_result + (\_\_first + \_\_count)

Like copy(), but does not require an initialized output range.

## Author

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