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<HEAD>
<Title>sparse_hash_map<Key, Data, HashFcn, EqualKey, Alloc></Title>
</HEAD>
<BODY>
<p><i>[Note: this document is formatted similarly to the SGI STL
implementation documentation pages, and refers to concepts and classes
defined there. However, neither this document nor the code it
describes is associated with SGI, nor is it necessary to have SGI's
STL implementation installed in order to use this class.]</i></p>
<H1>sparse_hash_map<Key, Data, HashFcn, EqualKey, Alloc></H1>
<p><tt>sparse_hash_map</tt> is a <A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A> that associates objects of type <tt>Key</tt>
with objects of type <tt>Data</tt>. <tt>sparse_hash_map</tt> is a <A
href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
Associative Container</A>, meaning that its value type is <tt><A
href="pair.html">pair</A><const Key, Data></tt>. It is also a
<A
href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
Associative Container</A>, meaning that no two elements have keys that
compare equal using <tt>EqualKey</tt>.</p>
<p>Looking up an element in a <tt>sparse_hash_map</tt> by its key is
efficient, so <tt>sparse_hash_map</tt> is useful for "dictionaries"
where the order of elements is irrelevant. If it is important for the
elements to be in a particular order, however, then <tt><A
href="http://www.sgi.com/tech/stl/Map.html">map</A></tt> is more appropriate.</p>
<p><tt>sparse_hash_map</tt> is distinguished from other hash-map
implementations by its stingy use of memory and by the ability to save
and restore contents to disk. On the other hand, this hash-map
implementation, while still efficient, is slower than other hash-map
implementations, and it also has requirements -- for instance, for a
distinguished "deleted key" -- that may not be easy for all
applications to satisfy.</p>
<p>This class is appropriate for applications that need to store
large "dictionaries" in memory, or for applications that need these
dictionaries to be persistent.</p>
<h3>Example</h3>
(Note: this example uses SGI semantics for <code>hash<></code>
-- the kind used by gcc and most Unix compiler suites -- and not
Dinkumware semantics -- the kind used by Microsoft Visual Studio. If
you are using MSVC, this example will not compile as-is: you'll need
to change <code>hash</code> to <code>hash_compare</code>, and you
won't use <code>eqstr</code> at all. See the MSVC documentation for
<code>hash_map</code> and <code>hash_compare</code>, for more
details.)
<pre>
#include <iostream>
#include <google/sparse_hash_map>
using google::sparse_hash_map; // namespace where class lives by default
using std::cout;
using std::endl;
using ext::hash; // or __gnu_cxx::hash, or maybe tr1::hash, depending on your OS
struct eqstr
{
bool operator()(const char* s1, const char* s2) const
{
return (s1 == s2) || (s1 && s2 && strcmp(s1, s2) == 0);
}
};
int main()
{
sparse_hash_map<const char*, int, hash<const char*>, eqstr> months;
months["january"] = 31;
months["february"] = 28;
months["march"] = 31;
months["april"] = 30;
months["may"] = 31;
months["june"] = 30;
months["july"] = 31;
months["august"] = 31;
months["september"] = 30;
months["october"] = 31;
months["november"] = 30;
months["december"] = 31;
cout << "september -> " << months["september"] << endl;
cout << "april -> " << months["april"] << endl;
cout << "june -> " << months["june"] << endl;
cout << "november -> " << months["november"] << endl;
}
</pre>
<h3>Definition</h3>
Defined in the header <A href="sparse_hash_map">sparse_hash_map</A>.
This class is not part of the C++ standard, though it is mostly
compatible with the tr1 class <code>unordered_map</code>.
<h3>Template parameters</h3>
<table border>
<TR><TH>Parameter</TH><TH>Description</TH><TH>Default</TH></TR>
<TR>
<TD VAlign=top>
<tt>Key</tt>
</TD>
<TD VAlign=top>
The hash_map's key type. This is also defined as
<tt>sparse_hash_map::key_type</tt>.
</TD>
<TD VAlign=top>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>Data</tt>
</TD>
<TD VAlign=top>
The hash_map's data type. This is also defined as
<tt>sparse_hash_map::data_type</tt>.
</TD>
<TD VAlign=top>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>HashFcn</tt>
</TD>
<TD VAlign=top>
The <A href="http://www.sgi.com/tech/stl/HashFunction.html">hash function</A> used by the
hash_map. This is also defined as <tt>sparse_hash_map::hasher</tt>.
<br><b>Note:</b> Hashtable performance depends heavily on the choice of
hash function. See <A HREF="performance.html#hashfn">the performance
page</A> for more information.
</TD>
<TD VAlign=top>
<tt><A href="http://www.sgi.com/tech/stl/hash.html">hash</A><Key></tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>EqualKey</tt>
</TD>
<TD VAlign=top>
The hash_map key equality function: a <A
href="http://www.sgi.com/tech/stl/BinaryPredicate.html">binary predicate</A> that determines
whether two keys are equal. This is also defined as
<tt>sparse_hash_map::key_equal</tt>.
</TD>
<TD VAlign=top>
<tt><A href="http://www.sgi.com/tech/stl/equal_to.html">equal_to</A><Key></tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>Alloc</tt>
</TD>
<TD VAlign=top>
The STL allocator to use. By default, uses the provided allocator
<code>libc_allocator_with_realloc</code>, which likely gives better
performance than other STL allocators due to its built-in support
for <code>realloc</code>, which this container takes advantage of.
If you use an allocator other than the default, note that this
container imposes an additional requirement on the STL allocator
type beyond those in [lib.allocator.requirements]: it does not
support allocators that define alternate memory models. That is,
it assumes that <code>pointer</code>, <code>const_pointer</code>,
<code>size_type</code>, and <code>difference_type</code> are just
<code>T*</code>, <code>const T*</code>, <code>size_t</code>, and
<code>ptrdiff_t</code>, respectively. This is also defined as
<tt>sparse_hash_map::allocator_type</tt>.
</TD>
<TD VAlign=top>
</TD>
</TR>
</table>
<h3>Model of</h3>
<A href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique Hashed Associative Container</A>,
<A href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair Associative Container</A>
<h3>Type requirements</h3>
<UL>
<LI>
<tt>Key</tt> is Assignable.
<LI>
<tt>EqualKey</tt> is a Binary Predicate whose argument type is Key.
<LI>
<tt>EqualKey</tt> is an equivalence relation.
<LI>
<tt>Alloc</tt> is an Allocator.
</UL>
<h3>Public base classes</h3>
None.
<h3>Members</h3>
<table border>
<TR><TH>Member</TH><TH>Where defined</TH><TH>Description</TH></TR>
<TR>
<TD VAlign=top>
<tt>key_type</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
The <tt>sparse_hash_map</tt>'s key type, <tt>Key</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>data_type</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
Associative Container</A>
</TD>
<TD VAlign=top>
The type of object associated with the keys.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>value_type</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
Associative Container</A>
</TD>
<TD VAlign=top>
The type of object, <tt>pair<const key_type, data_type></tt>,
stored in the hash_map.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>hasher</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
The <tt>sparse_hash_map</tt>'s <A
href="http://www.sgi.com/tech/stl/HashFunction.html">hash
function</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>key_equal</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/functors.html">Function
object</A> that compares keys for equality.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>allocator_type</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
The type of the Allocator given as a template parameter.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>pointer</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Pointer to <tt>T</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>reference</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Reference to <tt>T</tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_reference</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Const reference to <tt>T</tt>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
An unsigned integral type.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>difference_type</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
A signed integral type.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>iterator</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Iterator used to iterate through a <tt>sparse_hash_map</tt>. <A
href="#1">[1]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_iterator</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Const iterator used to iterate through a <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>local_iterator</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Iterator used to iterate through a subset of
<tt>sparse_hash_map</tt>. <A href="#1">[1]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_local_iterator</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Const iterator used to iterate through a subset of
<tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>iterator begin()</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Returns an <tt>iterator</tt> pointing to the beginning of the
<tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>iterator end()</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Returns an <tt>iterator</tt> pointing to the end of the
<tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_iterator begin() const</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Returns an <tt>const_iterator</tt> pointing to the beginning of the
<tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_iterator end() const</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Returns an <tt>const_iterator</tt> pointing to the end of the
<tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>local_iterator begin(size_type i)</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns a <tt>local_iterator</tt> pointing to the beginning of bucket
<tt>i</tt> in the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>local_iterator end(size_type i)</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns a <tt>local_iterator</tt> pointing to the end of bucket
<tt>i</tt> in the <tt>sparse_hash_map</tt>. For
<tt>sparse_hash_map</tt>, each bucket contains either 0 or 1 item.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_local_iterator begin(size_type i) const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns a <tt>const_local_iterator</tt> pointing to the beginning of bucket
<tt>i</tt> in the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_local_iterator end(size_type i) const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns a <tt>const_local_iterator</tt> pointing to the end of bucket
<tt>i</tt> in the <tt>sparse_hash_map</tt>. For
<tt>sparse_hash_map</tt>, each bucket contains either 0 or 1 item.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type size() const</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Returns the size of the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type max_size() const</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Returns the largest possible size of the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool empty() const</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
<tt>true</tt> if the <tt>sparse_hash_map</tt>'s size is <tt>0</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type bucket_count() const</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Returns the number of buckets used by the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type max_bucket_count() const</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Returns the largest possible number of buckets used by the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type bucket_size(size_type i) const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns the number of elements in bucket <tt>i</tt>. For
<tt>sparse_hash_map</tt>, this will be either 0 or 1.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type bucket(const key_type& key) const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
If the key exists in the map, returns the index of the bucket
containing the given key, otherwise, return the bucket the key
would be inserted into.
This value may be passed to <tt>begin(size_type)</tt> and
<tt>end(size_type)</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>float load_factor() const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
The number of elements in the <tt>sparse_hash_map</tt> divided by
the number of buckets.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>float max_load_factor() const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
The maximum load factor before increasing the number of buckets in
the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void max_load_factor(float new_grow)</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Sets the maximum load factor before increasing the number of
buckets in the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>float min_load_factor() const</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
The minimum load factor before decreasing the number of buckets in
the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void min_load_factor(float new_grow)</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
Sets the minimum load factor before decreasing the number of
buckets in the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void set_resizing_parameters(float shrink, float grow)</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
DEPRECATED. <A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void resize(size_type n)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Increases the bucket count to hold at least <tt>n</tt> items.
<A href="#4">[4]</A> <A href="#5">[5]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void rehash(size_type n)</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Increases the bucket count to hold at least <tt>n</tt> items.
This is identical to <tt>resize</tt>.
<A href="#4">[4]</A> <A href="#5">[5]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>hasher hash_funct() const</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Returns the <tt>hasher</tt> object used by the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>hasher hash_function() const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns the <tt>hasher</tt> object used by the <tt>sparse_hash_map</tt>.
This is idential to <tt>hash_funct</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>key_equal key_eq() const</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Returns the <tt>key_equal</tt> object used by the
<tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>allocator_type get_allocator() const</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Returns the <tt>allocator_type</tt> object used by the
<tt>sparse_hash_map</tt>: either the one passed in to the
constructor, or a default <tt>Alloc</tt> instance.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map()</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Creates an empty <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map(size_type n)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Creates an empty <tt>sparse_hash_map</tt> that's optimized for holding
up to <tt>n</tt> items.
<A href="#5">[5]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map(size_type n, const hasher& h)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Creates an empty <tt>sparse_hash_map</tt> that's optimized for up
to <tt>n</tt> items, using <tt>h</tt> as the hash function.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map(size_type n, const hasher& h, const
key_equal& k)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Creates an empty <tt>sparse_hash_map</tt> that's optimized for up
to <tt>n</tt> items, using <tt>h</tt> as the hash function and
<tt>k</tt> as the key equal function.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map(size_type n, const hasher& h, const
key_equal& k, const allocator_type& a)</tt>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Creates an empty <tt>sparse_hash_map</tt> that's optimized for up
to <tt>n</tt> items, using <tt>h</tt> as the hash function,
<tt>k</tt> as the key equal function, and <tt>a</tt> as the
allocator object.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>template <class <A
href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
sparse_hash_map(InputIterator f, InputIterator l) </pre>
<A href="#2">[2]</A>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
Hashed Associative Container</A>
</TD>
<TD VAlign=top>
Creates a sparse_hash_map with a copy of a range.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>template <class <A
href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
sparse_hash_map(InputIterator f, InputIterator l, size_type n) </pre>
<A href="#2">[2]</A>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
Hashed Associative Container</A>
</TD>
<TD VAlign=top>
Creates a hash_map with a copy of a range that's optimized to
hold up to <tt>n</tt> items.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>template <class <A
href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
sparse_hash_map(InputIterator f, InputIterator l, size_type n, const
hasher& h) </pre> <A href="#2">[2]</A>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
Hashed Associative Container</A>
</TD>
<TD VAlign=top>
Creates a hash_map with a copy of a range that's optimized to hold
up to <tt>n</tt> items, using <tt>h</tt> as the hash function.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>template <class <A
href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
sparse_hash_map(InputIterator f, InputIterator l, size_type n, const
hasher& h, const key_equal& k) </pre> <A href="#2">[2]</A>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
Hashed Associative Container</A>
</TD>
<TD VAlign=top>
Creates a hash_map with a copy of a range that's optimized for
holding up to <tt>n</tt> items, using <tt>h</tt> as the hash
function and <tt>k</tt> as the key equal function.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>template <class <A
href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
sparse_hash_map(InputIterator f, InputIterator l, size_type n, const
hasher& h, const key_equal& k, const allocator_type& a) </pre>
<A href="#2">[2]</A>
</TD>
<TD VAlign=top>
<tt>Unordered Associative Container</tt> (tr1)
</TD>
<TD VAlign=top>
Creates a hash_map with a copy of a range that's optimized for
holding up to <tt>n</tt> items, using <tt>h</tt> as the hash
function, <tt>k</tt> as the key equal function, and <tt>a</tt> as
the allocator object.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map(const hash_map&)</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
The copy constructor.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>sparse_hash_map& operator=(const hash_map&)</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
The assignment operator
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void swap(hash_map&)</tt>
</TD>
<TD VAlign=top>
<A href="http://www.sgi.com/tech/stl/Container.html">Container</A>
</TD>
<TD VAlign=top>
Swaps the contents of two hash_maps.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>pair<iterator, bool> insert(const value_type& x)
</pre>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
Associative Container</A>
</TD>
<TD VAlign=top>
Inserts <tt>x</tt> into the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>template <class <A
href="http://www.sgi.com/tech/stl/InputIterator.html">InputIterator</A>>
void insert(InputIterator f, InputIterator l) </pre> <A href="#2">[2]</A>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
Associative Container</A>
</TD>
<TD VAlign=top>
Inserts a range into the <tt>sparse_hash_map</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void set_deleted_key(const key_type& key)</tt> <A href="#6">[6]</A>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void clear_deleted_key()</tt> <A href="#6">[6]</A>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void erase(iterator pos)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Erases the element pointed to by <tt>pos</tt>.
<A href="#6">[6]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type erase(const key_type& k)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Erases the element whose key is <tt>k</tt>.
<A href="#6">[6]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void erase(iterator first, iterator last)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Erases all elements in a range.
<A href="#6">[6]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void clear()</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Erases all of the elements.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>const_iterator find(const key_type& k) const</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Finds an element whose key is <tt>k</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>iterator find(const key_type& k)</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Finds an element whose key is <tt>k</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>size_type count(const key_type& k) const</tt>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/UniqueAssociativeContainer.html">Unique
Associative Container</A>
</TD>
<TD VAlign=top>
Counts the number of elements whose key is <tt>k</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>pair<const_iterator, const_iterator> equal_range(const
key_type& k) const </pre>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Finds a range containing all elements whose key is <tt>k</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>pair<iterator, iterator> equal_range(const
key_type& k) </pre>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative
Container</A>
</TD>
<TD VAlign=top>
Finds a range containing all elements whose key is <tt>k</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>data_type& operator[](const key_type& k) <A
href="http://www.sgi.com/tech/stl/#3">[3]</A> </pre>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool write_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool read_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool write_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool read_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
<tt>sparse_hash_map</tt>
</TD>
<TD VAlign=top>
<A HREF="#new">See below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>bool operator==(const hash_map&, const hash_map&)
</pre>
</TD>
<TD VAlign=top>
<A
href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed
Associative Container</A>
</TD>
<TD VAlign=top>
Tests two hash_maps for equality. This is a global function, not a
member function.
</TD>
</TR>
</table>
<h3><A NAME="new">New members</A></h3>
These members are not defined in the <A
href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique
Hashed Associative Container</A>, <A
href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair
Associative Container</A>, or tr1's
<tt>Unordered Associative Container</tt> requirements,
but are specific to <tt>sparse_hash_map</tt>.
<table border>
<TR><TH>Member</TH><TH>Description</TH></TR>
<TR>
<TR>
<TD VAlign=top>
<tt>void set_deleted_key(const key_type& key)</tt>
</TD>
<TD VAlign=top>
Sets the distinguished "deleted" key to <tt>key</tt>. This must be
called before any calls to <tt>erase()</tt>. <A href="#6">[6]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>void clear_deleted_key()</tt>
</TD>
<TD VAlign=top>
Clears the distinguished "deleted" key. After this is called,
calls to <tt>erase()</tt> are not valid on this object.
<A href="#6">[6]</A>
</TD>
</TR>
<TR>
<TD VAlign=top>
<pre>
data_type&
operator[](const key_type& k) <A
href="http://www.sgi.com/tech/stl/#3">[3]</A>
</pre>
</TD>
<TD VAlign=top>
Returns a reference to the object that is associated with
a particular key. If the <tt>sparse_hash_map</tt> does not already
contain such an object, <tt>operator[]</tt> inserts the default
object <tt>data_type()</tt>. <A
href="http://www.sgi.com/tech/stl/#3">[3]</A>
</TD>
</TR>
<TD VAlign=top>
<tt>void set_resizing_parameters(float shrink, float grow)</tt>
</TD>
<TD VAlign=top>
This function is DEPRECATED. It is equivalent to calling
<tt>min_load_factor(shrink); max_load_factor(grow)</tt>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool write_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
Write hashtable metadata to <tt>fp</tt>. See <A HREF="#io">below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool read_metadata(FILE *fp)</tt>
</TD>
<TD VAlign=top>
Read hashtable metadata from <tt>fp</tt>. See <A HREF="#io">below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool write_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
Write hashtable contents to <tt>fp</tt>. This is valid only if the
hashtable key and value are "plain" data. See <A HREF="#io">below</A>.
</TD>
</TR>
<TR>
<TD VAlign=top>
<tt>bool read_nopointer_data(FILE *fp)</tt>
</TD>
<TD VAlign=top>
Read hashtable contents to <tt>fp</tt>. This is valid only if the
hashtable key and value are "plain" data. See <A HREF="#io">below</A>.
</TD>
</TR>
</table>
<h3>Notes</h3>
<P><A name="1">[1]</A>
<tt>sparse_hash_map::iterator</tt> is not a mutable iterator, because
<tt>sparse_hash_map::value_type</tt> is not <A
href="http://www.sgi.com/tech/stl/Assignable.html">Assignable</A>.
That is, if <tt>i</tt> is of type <tt>sparse_hash_map::iterator</tt>
and <tt>p</tt> is of type <tt>sparse_hash_map::value_type</tt>, then
<tt>*i = p</tt> is not a valid expression. However,
<tt>sparse_hash_map::iterator</tt> isn't a constant iterator either,
because it can be used to modify the object that it points to. Using
the same notation as above, <tt>(*i).second = p</tt> is a valid
expression.</p>
<P><A name="2">[2]</A>
This member function relies on <i>member template</i> functions, which
may not be supported by all compilers. If your compiler supports
member templates, you can call this function with any type of <A
href="http://www.sgi.com/tech/stl/InputIterator.html">input
iterator</A>. If your compiler does not yet support member templates,
though, then the arguments must either be of type <tt>const
value_type*</tt> or of type <tt>sparse_hash_map::const_iterator</tt>.</p>
<P><A name="3">[3]</A>
Since <tt>operator[]</tt> might insert a new element into the
<tt>sparse_hash_map</tt>, it can't possibly be a <tt>const</tt> member
function. Note that the definition of <tt>operator[]</tt> is
extremely simple: <tt>m[k]</tt> is equivalent to
<tt>(*((m.insert(value_type(k, data_type()))).first)).second</tt>.
Strictly speaking, this member function is unnecessary: it exists only
for convenience.</p>
<P><A name="4">[4]</A>
In order to preserve iterators, erasing hashtable elements does not
cause a hashtable to resize. This means that after a string of
<tt>erase()</tt> calls, the hashtable will use more space than is
required. At a cost of invalidating all current iterators, you can
call <tt>resize()</tt> to manually compact the hashtable. The
hashtable promotes too-small <tt>resize()</tt> arguments to the
smallest legal value, so to compact a hashtable, it's sufficient to
call <tt>resize(0)</tt>.
<P><A name="5">[5]</A>
Unlike some other hashtable implementations, the optional <i>n</i> in
the calls to the constructor, <tt>resize</tt>, and <tt>rehash</tt>
indicates not the desired number of buckets that
should be allocated, but instead the expected number of items to be
inserted. The class then sizes the hash-map appropriately for the
number of items specified. It's not an error to actually insert more
or fewer items into the hashtable, but the implementation is most
efficient -- does the fewest hashtable resizes -- if the number of
inserted items is <i>n</i> or slightly less.</p>
<P><A name="6">[6]</A>
<tt>sparse_hash_map</tt> <b>requires</b> you call
<tt>set_deleted_key()</tt> before calling <tt>erase()</tt>. (This is
the largest difference between the <tt>sparse_hash_map</tt> API and
other hash-map APIs. See <A HREF="implementation.html">implementation.html</A>
for why this is necessary.)
The argument to <tt>set_deleted_key()</tt> should be a key-value that
is never used for legitimate hash-map entries. It is an error to call
<tt>erase()</tt> without first calling <tt>set_deleted_key()</tt>, and
it is also an error to call <tt>insert()</tt> with an item whose key
is the "deleted key."</p>
<p>There is no need to call <tt>set_deleted_key</tt> if you do not
wish to call <tt>erase()</tt> on the hash-map.</p>
<p>It is acceptable to change the deleted-key at any time by calling
<tt>set_deleted_key()</tt> with a new argument. You can also call
<tt>clear_deleted_key()</tt>, at which point all keys become valid for
insertion but no hashtable entries can be deleted until
<tt>set_deleted_key()</tt> is called again.</p>
<p><b>Note:</b> If you use <tt>set_deleted_key</tt>, it is also
necessary that <tt>data_type</tt> has a zero-argument default
constructor. This is because <tt>sparse_hash_map</tt> uses the
special value <tt>pair(deleted_key, data_type())</tt> to denote
deleted buckets, and thus needs to be able to create
<tt>data_type</tt> using a zero-argument constructor.</p>
<p>If your <tt>data_type</tt> does not have a zero-argument default
constructor, there are several workarounds:</p>
<ul>
<li> Store a pointer to <tt>data_type</tt> in the map, instead of
<tt>data_type</tt> directly. This may yield faster code as
well, since hashtable-resizes will just have to move pointers
around, rather than copying the entire <tt>data_type</tt>.
<li> Add a zero-argument default constructor to <tt>data_type</tt>.
<li> Subclass <tt>data_type</tt> and add a zero-argument default
constructor to the subclass.
</ul>
<p>If you do not use <tt>set_deleted_key</tt>, then there is no
requirement that <tt>data_type</tt> havea zero-argument default
constructor.
<h3><A NAME=io>Input/Output</A></h3>
<p>It is possible to save and restore <tt>sparse_hash_map</tt> objects
to disk. Storage takes place in two steps. The first writes the
hashtable metadata. The second writes the actual data.</p>
<p>To write a hashtable to disk, first call <tt>write_metadata()</tt>
on an open file pointer. This saves the hashtable information in a
byte-order-independent format.</p>
<p>After the metadata has been written to disk, you must write the
actual data stored in the hash-map to disk. If both the key and data
are "simple" enough, you can do this by calling
<tt>write_nopointer_data()</tt>. "Simple" data is data that can be
safely copied to disk via <tt>fwrite()</tt>. Native C data types fall
into this category, as do structs of native C data types. Pointers
and STL objects do not.</p>
<p>Note that <tt>write_nopointer_data()</tt> does not do any endian
conversion. Thus, it is only appropriate when you intend to read the
data on the same endian architecture as you write the data.</p>
<p>If you cannot use <tt>write_nopointer_data()</tt> for any reason,
you can write the data yourself by iterating over the
<tt>sparse_hash_map</tt> with a <tt>const_iterator</tt> and writing
the key and data in any manner you wish.</p>
<p>To read the hashtable information from disk, first you must create
a <tt>sparse_hash_map</tt> object. Then open a file pointer to point
to the saved hashtable, and call <tt>read_metadata()</tt>. If you
saved the data via <tt>write_nopointer_data()</tt>, you can follow the
<tt>read_metadata()</tt> call with a call to
<tt>read_nopointer_data()</tt>. This is all that is needed.</p>
<p>If you saved the data through a custom write routine, you must call
a custom read routine to read in the data. To do this, iterate over
the <tt>sparse_hash_map</tt> with an <tt>iterator</tt>; this operation
is sensical because the metadata has already been set up. For each
iterator item, you can read the key and value from disk, and set it
appropriately. You will need to do a <tt>const_cast</tt> on the
iterator, since <tt>it->first</tt> is always <tt>const</tt>. You
will also need to use placement-new if the key or value is a C++
object. The code might look like this:</p>
<pre>
for (sparse_hash_map<int*, ComplicatedClass>::iterator it = ht.begin();
it != ht.end(); ++it) {
// The key is stored in the sparse_hash_map as a pointer
const_cast<int*>(it->first) = new int;
fread(const_cast<int*>(it->first), sizeof(int), 1, fp);
// The value is a complicated C++ class that takes an int to construct
int ctor_arg;
fread(&ctor_arg, sizeof(int), 1, fp);
new (&it->second) ComplicatedClass(ctor_arg); // "placement new"
}
</pre>
<h3><A NAME=iter>Validity of Iterators</A></h3>
<p><tt>erase()</tt> is guaranteed not to invalidate any iterators --
except for any iterators pointing to the item being erased, of course.
<tt>insert()</tt> invalidates all iterators, as does
<tt>resize()</tt>. </p>
<p>This is implemented by making <tt>erase()</tt> not resize the
hashtable. If you desire maximum space efficiency, you can call
<tt>resize(0)</tt> after a string of <tt>erase()</tt> calls, to force
the hashtable to resize to the smallest possible size.</p>
<p>In addition to invalidating iterators, <tt>insert()</tt>
and <tt>resize()</tt> invalidate all pointers into the hashtable. If
you want to store a pointer to an object held in a sparse_hash_map,
either do so after finishing hashtable inserts, or store the object on
the heap and a pointer to it in the sparse_hash_map.</p>
<h3>See also</h3>
<p>The following are SGI STL, and some Google STL, concepts and
classes related to <tt>sparse_hash_map</tt>.</p>
<tt><A href="http://www.sgi.com/tech/stl/hash_map.html">hash_map</A></tt>,
<A href="http://www.sgi.com/tech/stl/AssociativeContainer.html">Associative Container</A>,
<A href="http://www.sgi.com/tech/stl/HashedAssociativeContainer.html">Hashed Associative Container</A>,
<A href="http://www.sgi.com/tech/stl/PairAssociativeContainer.html">Pair Associative Container</A>,
<A href="http://www.sgi.com/tech/stl/UniqueHashedAssociativeContainer.html">Unique Hashed Associative Container</A>,
<tt><A href="http://www.sgi.com/tech/stl/set.html">set</A></tt>,
<tt><A href="http://www.sgi.com/tech/stl/Map.html">map</A></tt>
<tt><A href="http://www.sgi.com/tech/stl/multiset.html">multiset</A></tt>,
<tt><A href="http://www.sgi.com/tech/stl/Multimap.html">multimap</A></tt>,
<tt><A href="http://www.sgi.com/tech/stl/hash_set.html">hash_set</A></tt>,
<tt><A href="http://www.sgi.com/tech/stl/hash_multiset.html">hash_multiset</A></tt>,
<tt><A href="http://www.sgi.com/tech/stl/hash_multimap.html">hash_multimap</A></tt>,
<tt><A href="sparsetable.html">sparsetable</A></tt>,
<tt><A href="sparse_hash_set.html">sparse_hash_set</A></tt>,
<tt><A href="dense_hash_set.html">dense_hash_set</A></tt>,
<tt><A href="dense_hash_map.html">dense_hash_map</A></tt>
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