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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 <string></span>
bool operator<span class="sy0">==</span><span class="br0">(</span><span class="kw4">const</span> string<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<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> string<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<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> string<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<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> string<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<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> string<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<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> string<span class="sy0">&</span> c1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&</span> c2<span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">(</span><span class="kw4">const</span> string<span class="sy0">&</span> s1<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&</span> s2 <span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">(</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">&</span> s2 <span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">(</span> Char c<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&</span> s2 <span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">(</span> <span class="kw4">const</span> string<span class="sy0">&</span> s1<span class="sy0">,</span> <span class="kw4">const</span> Char<span class="sy0">*</span> s <span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">string</span> operator<span class="sy0">+</span><span class="br0">(</span> <span class="kw4">const</span> string<span class="sy0">&</span> s1<span class="sy0">,</span> Char c <span class="br0">)</span><span class="sy0">;</span>
string<span class="sy0">&</span> operator<span class="sy0">+=</span><span class="br0">(</span><span class="kw4">const</span> string<span class="sy0">&</span> append<span class="br0">)</span><span class="sy0">;</span>
string<span class="sy0">&</span> operator<span class="sy0">+=</span><span class="br0">(</span><span class="kw4">const</span> Char<span class="sy0">*</span> append<span class="br0">)</span><span class="sy0">;</span>
string<span class="sy0">&</span> operator<span class="sy0">+=</span><span class="br0">(</span><span class="kw4">const</span> Char append<span class="br0">)</span><span class="sy0">;</span>
ostream<span class="sy0">&</span> operator<span class="sy0"><<</span><span class="br0">(</span> ostream<span class="sy0">&</span> os<span class="sy0">,</span> <span class="kw4">const</span> string<span class="sy0">&</span> s <span class="br0">)</span><span class="sy0">;</span>
istream<span class="sy0">&</span> operator<span class="sy0">>></span><span class="br0">(</span> istream<span class="sy0">&</span> is<span class="sy0">,</span> string<span class="sy0">&</span> s <span class="br0">)</span><span class="sy0">;</span>
string<span class="sy0">&</span> operator<span class="sy0">=</span><span class="br0">(</span> <span class="kw4">const</span> string<span class="sy0">&</span> s <span class="br0">)</span><span class="sy0">;</span>
string<span class="sy0">&</span> operator<span class="sy0">=</span><span class="br0">(</span> <span class="kw4">const</span> Char<span class="sy0">*</span> s <span class="br0">)</span><span class="sy0">;</span>
string<span class="sy0">&</span> operator<span class="sy0">=</span><span class="br0">(</span> Char ch <span class="br0">)</span><span class="sy0">;</span>
Char<span class="sy0">&</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span> size_type index <span class="br0">)</span><span class="sy0">;</span>
<span class="kw4">const</span> Char<span class="sy0">&</span> operator<span class="br0">[</span><span class="br0">]</span><span class="br0">(</span> size_type index <span class="br0">)</span> <span class="kw4">const</span><span class="sy0">;</span></pre>
<p>
C++ strings can be compared and assigned with the standard comparison
operators: ==, !=, <=, >=, <, >, 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 << and >>
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">"Now is the time..."</span><span class="sy0">;</span>
<span class="kw4">string</span> s2 <span class="sy0">=</span> <span class="st0">"for all good men..."</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"><<</span> <span class="st0">"s3 is "</span> <span class="sy0"><<</span> s3 <span class="sy0"><<</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>
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