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Map operators [C++ Reference]
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<h2><a name="map_operators" id="map_operators">Map operators</a></h2>
<div class="level2">
<p>
Syntax:
</p>
<pre class="c code c++" style="font-family:monospace;"> <span class="co2">#include <map></span>
mapped_type<span class="sy0">&</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span> <span class="kw4">const</span> key_type<span class="sy0">&</span> key <span class="br0">)</span><span class="sy0">;</span>
map<span class="sy0">&</span> operator<span class="sy0">=</span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
bool operator<span class="sy0">==</span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
bool operator<span class="sy0">!=</span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
bool operator<span class="sy0"><</span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
bool operator<span class="sy0">></span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
bool operator<span class="sy0"><=</span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
bool operator<span class="sy0">>=</span><span class="br0">(</span><span class="kw4">const</span> map<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> map<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span></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" class="wikilink1" title="complexity">linear time</a>.
</p>
<p>
Two maps are equal if:
</p>
<ol>
<li class="level1"><div class="li"> Their size is the same, and</div>
</li>
<li class="level1"><div class="li"> Each member in location i in one map is equal to the the member in location i in the other map.</div>
</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="c code c++" style="font-family:monospace;"> <span class="kw4">struct</span> strCmp <span class="br0">{</span>
bool operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy0">*</span> s1<span class="sy0">,</span> <span class="kw4">const</span> <span class="kw4">char</span><span class="sy0">*</span> s2 <span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
<span class="kw1">return</span> strcmp<span class="br0">(</span> s1<span class="sy0">,</span> s2 <span class="br0">)</span> <span class="sy0"><</span> <span class="nu0">0</span><span class="sy0">;</span>
<span class="br0">}</span>
<span class="br0">}</span><span class="sy0">;</span>
map<span class="sy0"><</span>const <span class="kw4">char</span><span class="sy0">*,</span> <span class="kw4">int</span><span class="sy0">,</span> strCmp<span class="sy0">></span> ages<span class="sy0">;</span>
ages<span class="br0">[</span><span class="st0">"Homer"</span><span class="br0">]</span> <span class="sy0">=</span> <span class="nu0">38</span><span class="sy0">;</span>
ages<span class="br0">[</span><span class="st0">"Marge"</span><span class="br0">]</span> <span class="sy0">=</span> <span class="nu0">37</span><span class="sy0">;</span>
ages<span class="br0">[</span><span class="st0">"Lisa"</span><span class="br0">]</span> <span class="sy0">=</span> <span class="nu0">8</span><span class="sy0">;</span>
ages<span class="br0">[</span><span class="st0">"Maggie"</span><span class="br0">]</span> <span class="sy0">=</span> <span class="nu0">1</span><span class="sy0">;</span>
ages<span class="br0">[</span><span class="st0">"Bart"</span><span class="br0">]</span> <span class="sy0">=</span> <span class="nu0">11</span><span class="sy0">;</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="st0">"Bart is "</span> <span class="sy0"><<</span> ages<span class="br0">[</span><span class="st0">"Bart"</span><span class="br0">]</span> <span class="sy0"><<</span> <span class="st0">" years old"</span> <span class="sy0"><<</span> endl<span class="sy0">;</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="st0">"In alphabetical order: "</span> <span class="sy0"><<</span> endl<span class="sy0">;</span>
<span class="kw1">for</span><span class="br0">(</span> map<span class="sy0"><</span>const <span class="kw4">char</span><span class="sy0">*,</span> <span class="kw4">int</span><span class="sy0">,</span> strCmp<span class="sy0">>::</span><span class="me2">iterator</span> iter <span class="sy0">=</span> ages.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">;</span> iter <span class="sy0">!=</span> ages.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">;</span> <span class="sy0">++</span>iter <span class="br0">)</span> <span class="br0">{</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> <span class="br0">(</span><span class="sy0">*</span>iter<span class="br0">)</span>.<span class="me1">first</span> <span class="sy0"><<</span> <span class="st0">" is "</span> <span class="sy0"><<</span> <span class="br0">(</span><span class="sy0">*</span>iter<span class="br0">)</span>.<span class="me1">second</span> <span class="sy0"><<</span> <span class="st0">" years old"</span> <span class="sy0"><<</span> endl<span class="sy0">;</span>
<span class="br0">}</span></pre>
<p>
When run, the above code displays this output:
</p>
<pre class="code">
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>
<p>
Related Topics: <a href="../../stl/map/insert.html" class="wikilink1" title="stl:map:insert">insert</a>, <a href="../../stl/map/map.html" class="wikilink1" title="stl:map:map_constructors">Map Constructors & Destructors</a>
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