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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<!-- Mirrored from cppreference.com/cppmap/all.html by HTTrack Website Copier/3.x [XR&CO'2004], Tue, 22 Jan 2008 06:25:39 GMT -->
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<head>
<meta name="generator" content=
"HTML Tidy for Linux/x86 (vers 1 September 2005), see www.w3.org">
<title>C++ Maps</title>
<link href="../cppreference.css" rel="stylesheet" type="text/css">
<link href="../prettify.css" type="text/css" rel="stylesheet" />
<script type="text/javascript" src="../prettify.js"></script>
</head>
<body onload="prettyPrint()">
<table>
<tr>
<td>
<div class="body-content">
<div class="header-box">
<a href="../index-2.html">cppreference.com</a> > <a href=
"index.html">C++ Maps</a>
</div>
<div class="name-format">
begin
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
iterator begin();
const_iterator begin() const;
</pre>
<p>The function begin() returns an iterator to the first element of
the map. begin() should run in <a href="../complexity.html">constant
time</a>.</p>
<p>For example, the following code uses begin() to initialize an
iterator that is used to traverse a list:</p>
<pre class="prettyprint">
map<string,int> stringCounts;
string str;
while( cin >> str ) stringCounts[str]++;
map<string,int>::iterator iter;
for( iter = stringCounts.begin(); iter != stringCounts.end(); iter++ ) {
cout << "word: " << iter->first << ", count: " << iter->second << endl;
}
</pre>
<p>When given this input:</p>
<pre class="prettyprint">
here are some words and here are some more words
</pre>
<p>...the above code generates this output:</p>
<pre class="prettyprint">
word: and, count: 1
word: are, count: 2
word: here, count: 2
word: more, count: 1
word: some, count: 2
word: words, count: 2
</pre>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="end.html">end</a><br>
<a href="rbegin.html">rbegin</a><br>
<a href="rend.html">rend</a>
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<hr>
<div class="name-format">
clear
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
void clear();
</pre>
<p>The function clear() deletes all of the elements in the map.
clear() runs in <a href="../complexity.html">linear time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="erase.html">erase</a>
</div>
</div>
</td>
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<hr>
<div class="name-format">
count
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
<strong>size_type</strong> count( const <a href=
"../containers.html">key_type</a>& key );
</pre>
<p>The function count() returns the number of occurrences of
<em>key</em> in the map.</p>
<p>count() should run in <a href="../complexity.html">logarithmic
time</a>.</p>
</div>
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<hr>
<div class="name-format">
empty
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
bool empty() const;
</pre>
<p>The empty() function returns true if the map has no elements,
false otherwise.</p>
<p>For example, the following code uses empty() as the stopping
condition on a <a href= "../keywords/while.html">while</a> loop to
clear a map and display its contents in order:</p>
<pre class="prettyprint">
struct strCmp {
bool operator()( const char* s1, const char* s2 ) const {
return strcmp( s1, s2 ) < 0;
}
};
...
map<const char*, int, strCmp> ages;
ages["Homer"] = 38;
ages["Marge"] = 37;
ages["Lisa"] = 8;
ages["Maggie"] = 1;
ages["Bart"] = 11;
while( !ages.empty() ) {
cout << "Erasing: " << (*ages.begin()).first << ", " << (*ages.begin()).second << endl;
ages.erase( ages.begin() );
}
</pre>
<p>When run, the above code displays:</p>
<pre class="prettyprint">
Erasing: Bart, 11
Erasing: Homer, 38
Erasing: Lisa, 8
Erasing: Maggie, 1
Erasing: Marge, 37
</pre>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="begin.html">begin</a><br>
<a href="erase.html">erase</a><br>
<a href="size.html">size</a>
</div>
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<hr>
<div class="name-format">
end
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
iterator end();
const_iterator end() const;
</pre>
<p>The end() function returns an iterator just past the end of the
map.</p>
<p>Note that before you can access the last element of the map using
an iterator that you get from a call to end(), you'll have to
decrement the iterator first.</p>
<p>For example, the following code uses <a href=
"begin.html">begin</a>() and end() to iterate through all of the
members of a vector:</p>
<pre class="prettyprint">
vector<int> v1( 5, 789 );
vector<int>::iterator it;
for( it = v1.begin(); it != v1.end(); it++ ) {
cout << *it << endl;
}
</pre>
<p>The iterator is initialized with a call to <a href=
"begin.html">begin</a>(). After the body of the loop has been
executed, the iterator is incremented and tested to see if it is
equal to the result of calling end(). Since end() returns an iterator
pointing to an element just after the last element of the vector, the
loop will only stop once all of the elements of the vector have been
displayed.</p>
<p>end() runs in <a href="../complexity.html">constant time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="begin.html">begin</a><br>
<a href="rbegin.html">rbegin</a><br>
<a href="rend.html">rend</a>
</div>
</div>
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<hr>
<div class="name-format">
equal_range
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
pair<iterator, iterator> equal_range( const <a href=
"../containers.html">key_type</a>& key );
</pre>
<p>The function equal_range() returns two iterators - one to the
first element that contains <em>key</em>, another to a point just
after the last element that contains <em>key</em>.</p>
</div>
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<hr>
<div class="name-format">
erase
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
void erase( iterator pos );
void erase( iterator start, iterator end );
<strong>size_type</strong> erase( const <a href=
"../containers.html">key_type</a>& key );
</pre>
<p>The erase function() either erases the element at <em>pos</em>,
erases the elements between <em>start</em> and <em>end</em>, or
erases all elements that have the value of <em>key</em>.</p>
<p>For example, the following code uses erase() in a <a href=
"../keywords/while.html">while</a> loop to incrementally clear a map
and display its contents in order:</p>
<pre class="prettyprint">
struct strCmp {
bool operator()( const char* s1, const char* s2 ) const {
return strcmp( s1, s2 ) < 0;
}
};
...
map<const char*, int, strCmp> ages;
ages["Homer"] = 38;
ages["Marge"] = 37;
ages["Lisa"] = 8;
ages["Maggie"] = 1;
ages["Bart"] = 11;
while( !ages.empty() ) {
cout << "Erasing: " << (*ages.begin()).first << ", " << (*ages.begin()).second << endl;
ages.erase( ages.begin() );
}
</pre>
<p>When run, the above code displays:</p>
<pre class="prettyprint">
Erasing: Bart, 11
Erasing: Homer, 38
Erasing: Lisa, 8
Erasing: Maggie, 1
Erasing: Marge, 37
</pre>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="begin.html">begin</a><br>
<a href="clear.html">clear</a><br>
<a href="empty.html">empty</a><br>
<a href="size.html">size</a>
</div>
</div>
</td>
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<hr>
<div class="name-format">
find
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
iterator find( const <a href=
"../containers.html">key_type</a>& key );
</pre>
<p>The find() function returns an iterator to <em>key</em>, or an
iterator to the end of the map if <em>key</em> is not found.</p>
<p>find() runs in <a href="../complexity.html">logarithmic
time</a>.</p>
<p>For example, the following code uses the find() function to
determine how many times a user entered a certain word:</p>
<pre class="prettyprint">
map<string,int> stringCounts;
string str;
while( cin >> str ) stringCounts[str]++;
map<string,int>::iterator iter = stringCounts.find("spoon");
if( iter != stringCounts.end() ) {
cout << "You typed '" << iter->first << "' " << iter->second << " time(s)" << endl;
}
</pre>
<p>When run with this input:</p>
<pre class="prettyprint">
my spoon is too big. my spoon is TOO big! my SPOON is TOO big! I am a BANANA!
</pre>
<p>...the above code produces this output:</p>
<pre class="prettyprint">
You typed 'spoon' 2 time(s)
</pre>
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<hr>
<div class="name-format">
insert
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
iterator insert( iterator i, const <a href=
"../containers.html">TYPE</a>& pair );
void insert( <a href=
"../iterators.html">input_iterator</a> start, <a href=
"../iterators.html">input_iterator</a> end );
pair<iterator,bool> insert( const <a href=
"../containers.html">TYPE</a>& pair );
</pre>
<p>The function insert() either:</p>
<ul>
<li>inserts <em>pair</em> after the element at <em>pos</em> (where
<em>pos</em> is really just a suggestion as to where <em>pair</em>
should go, since sets and maps are ordered), and returns an
iterator to that element.</li>
<li>inserts a range of elements from <em>start</em> to
<em>end</em>.</li>
<li>inserts <em>pair</em><<em>key</em>,<em>val</em>>, but only
if no element with key <em>key</em> already exists. The return value
is an iterator to the element inserted (or an existing pair with key
<em>key</em>), and a boolean which is true if an insertion took place.</li>
</ul>
<p>For example, the following code uses the insert() function (along
with the make_pair() function) to insert some data into a map and
then displays that data:</p>
<pre class="prettyprint">
map<string,int> theMap;
theMap.insert( make_pair( "Key 1", -1 ) );
theMap.insert( make_pair( "Another key!", 32 ) );
theMap.insert( make_pair( "Key the Three", 66667 ) );
map<string,int>::iterator iter;
for( iter = theMap.begin(); iter != theMap.end(); ++iter ) {
cout << "Key: '" << iter->first << "', Value: " << iter->second << endl;
}
</pre>
<p>When run, the above code displays this output:</p>
<pre class="prettyprint">
Key: 'Another key!', Value: 32
Key: 'Key 1', Value: -1
Key: 'Key the Three', Value: 66667
</pre>
<p>Note that because maps are sorted containers, the output is
sorted by the key value. In this case, since the map key data type
is <a href="../cppstring/index.html">string</a>, the map is sorted
alphabetically by key.</p>
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Related topics:
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<a href="map_operators.html">Map operators</a>
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<div class="name-format">
key_comp
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
key_compare key_comp() const;
</pre>
<p>The function key_comp() returns the function that compares
keys.</p>
<p>key_comp() runs in <a href="../complexity.html">constant
time</a>.</p>
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<a href="value_comp.html">value_comp</a>
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<div class="name-format">
lower_bound
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
iterator lower_bound( const <a href=
"../containers.html">key_type</a>& key );
</pre>
<p>The lower_bound() function returns an iterator to the first
element which has a value greater than or equal to key.</p>
<p>lower_bound() runs in <a href="../complexity.html">logarithmic
time</a>.</p>
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<a href="upper_bound.html">upper_bound</a>
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<div class="name-format">
Map Constructors & Destructors
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
map();
map( const map& m );
map( iterator start, iterator end );
map( iterator start, iterator end, const key_compare& cmp );
map( const key_compare& cmp );
~map();
</pre>
<p>The default constructor takes no arguments, creates a new instance
of that map, and runs in <a href="../complexity.html">constant
time</a>. The default copy constructor runs in <a href=
"../complexity.html">linear time</a> and can be used to create a new
map that is a copy of the given map <em>m</em>.</p>
<p>You can also create a map that will contain a copy of the
elements between <em>start</em> and <em>end</em>, or specify a
comparison function <em>cmp</em>.
<p>The default destructor is called when the map should be
destroyed.</p>
<p>For example, the following code creates a map that associates a
string with an integer:</p>
<pre class="prettyprint">
struct strCmp {
bool operator()( const char* s1, const char* s2 ) const {
return strcmp( s1, s2 ) < 0;
}
};
...
map<const char*, int, strCmp> ages;
ages["Homer"] = 38;
ages["Marge"] = 37;
ages["Lisa"] = 8;
ages["Maggie"] = 1;
ages["Bart"] = 11;
cout << "Bart is " << ages["Bart"] << " years old" << endl;
</pre>
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Related topics:
</div>
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<a href="map_operators.html">Map Operators</a>
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<div class="name-format">
Map operators
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
<a href="../containers.html">TYPE</a>& operator[]( const <a href=
"../containers.html">key_type</a>& key );
map operator=(const map& c2);
bool operator==(const map& c1, const map& c2);
bool operator!=(const map& c1, const map& c2);
bool operator<(const map& c1, const map& c2);
bool operator>(const map& c1, const map& c2);
bool operator<=(const map& c1, const map& c2);
bool operator>=(const map& c1, const map& c2);
</pre>
<p>Maps can be compared and assigned with the standard comparison
operators: ==, !=, <=, >=, <, >, and =. Individual
elements of a map can be examined with the [] operator.</p>
<p>Performing a comparison or assigning one map to another takes
<a href="../complexity.html">linear time</a>.</p>
<p>Two maps are equal if:</p>
<ol>
<li>Their size is the same, and</li>
<li>Each member in location <em>i</em> in one map is equal to the
the member in location <em>i</em> in the other map.</li>
</ol>
<p>Comparisons among maps are done lexicographically.</p>
<p>For example, the following code defines a map between strings and
integers and loads values into the map using the [] operator:</p>
<pre class="prettyprint">
struct strCmp {
bool operator()( const char* s1, const char* s2 ) const {
return strcmp( s1, s2 ) < 0;
}
};
map<const char*, int, strCmp> ages;
ages["Homer"] = 38;
ages["Marge"] = 37;
ages["Lisa"] = 8;
ages["Maggie"] = 1;
ages["Bart"] = 11;
cout << "Bart is " << ages["Bart"] << " years old" << endl;
cout << "In alphabetical order: " << endl;
for( map<const char*, int, strCmp>::iterator iter = ages.begin(); iter != ages.end(); iter++ ) {
cout << (*iter).first << " is " << (*iter).second << " years old" << endl;
}
</pre>
<p>When run, the above code displays this output:</p>
<pre class="prettyprint">
Bart is 11 years old
In alphabetical order:
Bart is 11 years old
Homer is 38 years old
Lisa is 8 years old
Maggie is 1 years old
Marge is 37 years old
</pre>
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Related topics:
</div>
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<a href="insert.html">insert</a><br>
<a href="map_constructors.html">Map Constructors & Destructors</a>
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<div class="name-format">
max_size
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
<strong>size_type</strong> max_size() const;
</pre>
<p>The max_size() function returns the maximum number of elements
that the map can hold. The max_size() function should not be confused
with the <a href="size.html">size</a>() or (C++ Strings) <a href=
"../cppstring/capacity.html">capacity</a>() functions, which return
the number of elements currently in the map and the the number of
elements that the map will be able to hold before more memory will
have to be allocated, respectively.</p>
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<a href="size.html">size</a>
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rbegin
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
<a href="../iterators.html">reverse_iterator</a> rbegin();
const_<a href=
"../iterators.html">reverse_iterator</a> rbegin() const;
</pre>
<p>The rbegin() function returns a <a href=
"../iterators.html">reverse_iterator</a> to the end of the current
map.</p>
<p>rbegin() runs in <a href="../complexity.html">constant
time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
<div class="related-content">
<a href="begin.html">begin</a><br>
<a href="end.html">end</a><br>
<a href="rend.html">rend</a>
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rend
</div>
<div class="syntax-name-format">
Syntax:
</div>
<pre class="syntax-box">
#include <map>
<a href="../iterators.html">reverse_iterator</a> rend();
const_<a href="../iterators.html">reverse_iterator</a> rend() const;
</pre>
<p>The function rend() returns a <a href=
"../iterators.html">reverse_iterator</a> to the beginning of the
current map.</p>
<p>rend() runs in <a href="../complexity.html">constant time</a>.</p>
<div class="related-name-format">
Related topics:
</div>
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<a href="begin.html">begin</a><br>
<a href="end.html">end</a><br>
<a href="rbegin.html">rbegin</a>
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size
</div>
<div class="syntax-name-format">
Syntax:
</div>