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    String operators    [C++ Reference]
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<h2><a name="string_operators" id="string_operators">String operators</a></h2>
<div class="level2">

<p>
Syntax:
</p>
<pre class="c code c++" style="font-family:monospace;">    <span class="co2">#include &lt;string&gt;</span>
    bool operator<span class="sy0">==</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> c2<span class="br0">&#41;</span><span class="sy0">;</span>
    bool operator<span class="sy0">!=</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> c2<span class="br0">&#41;</span><span class="sy0">;</span>
    bool operator<span class="sy0">&lt;</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> c2<span class="br0">&#41;</span><span class="sy0">;</span>
    bool operator<span class="sy0">&gt;</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> c2<span class="br0">&#41;</span><span class="sy0">;</span>
    bool operator<span class="sy0">&lt;=</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> c2<span class="br0">&#41;</span><span class="sy0">;</span>
    bool operator<span class="sy0">&gt;=</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> c2<span class="br0">&#41;</span><span class="sy0">;</span>
    <span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> s1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s2 <span class="br0">&#41;</span><span class="sy0">;</span>
    <span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">&#40;</span><span class="kw4">const</span> Char<span class="sy0">*</span> s<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s2 <span class="br0">&#41;</span><span class="sy0">;</span>
    <span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">&#40;</span> Char c<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s2 <span class="br0">&#41;</span><span class="sy0">;</span>
    <span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">&#40;</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s1<span class="sy0">,</span> <span class="kw4">const</span> Char<span class="sy0">*</span> s <span class="br0">&#41;</span><span class="sy0">;</span>
    <span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">&#40;</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s1<span class="sy0">,</span> Char c <span class="br0">&#41;</span><span class="sy0">;</span>
    string<span class="sy0">&amp;</span> operator<span class="sy0">+=</span><span class="br0">&#40;</span><span class="kw4">const</span> string<span class="sy0">&amp;</span> append<span class="br0">&#41;</span><span class="sy0">;</span>
    string<span class="sy0">&amp;</span> operator<span class="sy0">+=</span><span class="br0">&#40;</span><span class="kw4">const</span> Char<span class="sy0">*</span> append<span class="br0">&#41;</span><span class="sy0">;</span>
    string<span class="sy0">&amp;</span> operator<span class="sy0">+=</span><span class="br0">&#40;</span><span class="kw4">const</span> Char  append<span class="br0">&#41;</span><span class="sy0">;</span>
    ostream<span class="sy0">&amp;</span> operator<span class="sy0">&lt;&lt;</span><span class="br0">&#40;</span> ostream<span class="sy0">&amp;</span> os<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s <span class="br0">&#41;</span><span class="sy0">;</span>
    istream<span class="sy0">&amp;</span> operator<span class="sy0">&gt;&gt;</span><span class="br0">&#40;</span> istream<span class="sy0">&amp;</span> is<span class="sy0">,</span> string<span class="sy0">&amp;</span> s <span class="br0">&#41;</span><span class="sy0">;</span>
    string<span class="sy0">&amp;</span> operator<span class="sy0">=</span><span class="br0">&#40;</span> <span class="kw4">const</span> string<span class="sy0">&amp;</span> s <span class="br0">&#41;</span><span class="sy0">;</span>
    string<span class="sy0">&amp;</span> operator<span class="sy0">=</span><span class="br0">&#40;</span> <span class="kw4">const</span> Char<span class="sy0">*</span> s <span class="br0">&#41;</span><span class="sy0">;</span>
    string<span class="sy0">&amp;</span> operator<span class="sy0">=</span><span class="br0">&#40;</span> Char ch <span class="br0">&#41;</span><span class="sy0">;</span>
    Char<span class="sy0">&amp;</span> operator<span class="br0">&#91;</span><span class="br0">&#93;</span><span class="br0">&#40;</span> size_type index <span class="br0">&#41;</span><span class="sy0">;</span>
    <span class="kw4">const</span> Char<span class="sy0">&amp;</span> operator<span class="br0">&#91;</span><span class="br0">&#93;</span><span class="br0">&#40;</span> size_type index <span class="br0">&#41;</span> <span class="kw4">const</span><span class="sy0">;</span></pre>
<p>
C++ strings can be compared and assigned with the standard comparison
operators: ==, !=, &lt;=, &gt;=, &lt;, &gt;, and =. Performing a comparison or assigning
one string to another takes <a href="../complexity.html" class="wikilink1" title="complexity">linear time</a>.
</p>

<p>
Two strings 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 string is equal to the the member in location i in the other string.</div>
</li>
</ol>

<p>

Comparisons among strings are done lexicographically.
</p>

<p>
In addition to the normal container operators, strings can also be concatenated
with the + operator and fed to the <a href="../io/start.html" class="wikilink1" title="io:start">C++ I/O stream classes</a> with the &lt;&lt; and &gt;&gt;
operators.
</p>

<p>
For example, the following code concatenates two strings and displays the
result:
</p>
<pre class="c code c++" style="font-family:monospace;">   <span class="kw4">string</span> s1 <span class="sy0">=</span> <span class="st0">&quot;Now is the time...&quot;</span><span class="sy0">;</span>
   <span class="kw4">string</span> s2 <span class="sy0">=</span> <span class="st0">&quot;for all good men...&quot;</span><span class="sy0">;</span>
   <span class="kw4">string</span> s3 <span class="sy0">=</span> s1 <span class="sy0">+</span> s2<span class="sy0">;</span>
   <a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0">&lt;&lt;</span> <span class="st0">&quot;s3 is &quot;</span> <span class="sy0">&lt;&lt;</span> s3 <span class="sy0">&lt;&lt;</span> endl<span class="sy0">;</span></pre>
<p>

Furthermore, strings can be assigned values that are other strings, character
arrays, or even single characters. The following code is perfectly valid:
</p>
<pre class="c code c++" style="font-family:monospace;">   <span class="kw4">char</span> ch <span class="sy0">=</span> <span class="st0">'N'</span><span class="sy0">;</span>
   <span class="kw4">string</span> s<span class="sy0">;</span>
   s <span class="sy0">=</span> ch<span class="sy0">;</span></pre>
<p>

Individual characters of a string can be examined with the [] operator, which
runs in <a href="../complexity.html" class="wikilink1" title="complexity">constant time</a>.
</p>

<p>
Related Topics: <a href="../string/c_str.html" class="wikilink1" title="string:c_str">c_str</a>, <a href="../string/compare.html" class="wikilink1" title="string:compare">compare</a>, <a href="../string/data.html" class="wikilink1" title="string:data">data</a>
</p>

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