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transform [C++ Reference]
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<h2><a name="transform" id="transform">transform</a></h2>
<div class="level2">
<p>
Syntax:
</p>
<pre class="c code c++" style="font-family:monospace;"> <span class="co2">#include <algorithm></span>
output_iterator transform<span class="br0">(</span> input_iterator start<span class="sy0">,</span> input_iterator end<span class="sy0">,</span> output_iterator result<span class="sy0">,</span> UnaryFunction f <span class="br0">)</span><span class="sy0">;</span>
output_iterator transform<span class="br0">(</span> input_iterator start1<span class="sy0">,</span> input_iterator end1<span class="sy0">,</span> input_iterator2 start2<span class="sy0">,</span> output_iterator result<span class="sy0">,</span> BinaryFunction f <span class="br0">)</span><span class="sy0">;</span></pre>
<p>
The <code>transform</code> algorithm applies the function <code>f</code> to some range of elements,
storing the result of each application of the function in <code>result</code>.
</p>
<p>
The first version of the function applies <code>f</code> to each element in <code>[start,end)</code> and
assigns the first output of the function to <code>result</code>, the second output to
<code>(result+1)</code>, etc.
</p>
<p>
The second version of the transform works in a similar manner, except that it
is given two ranges of elements and calls a binary function on a pair of
elements.
</p>
<p>
For example, the following code uses transform to convert a <a href="../../string/start.html" class="wikilink1" title="string:start">string</a> to
uppercase using the <a href="../../c/string/toupper.html" class="wikilink1" title="c:string:toupper">toupper function</a>:
</p>
<pre class="c code c++" style="font-family:monospace;"> <span class="kw4">string</span> s<span class="br0">(</span><span class="st0">"hello"</span><span class="br0">)</span><span class="sy0">;</span>
transform<span class="br0">(</span>s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> s.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> s.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> toupper<span class="br0">)</span><span class="sy0">;</span>
<span class="co1">// in some compilers, you have to add a cast to "toupper" to resolve ambiguity:</span>
<span class="co1">// transform(s.begin(), s.end(), s.begin(), (int (*)(int))toupper);</span>
<a href="http://www.opengroup.org/onlinepubs/009695399/functions/cout.html"><span class="kw3">cout</span></a> <span class="sy0"><<</span> s <span class="sy0"><<</span> endl<span class="sy0">;</span></pre>
<p>
The above code displays the following output:
</p>
<pre class="code">
HELLO</pre>
<p>
Alternatively, the following example shows how user-defined functions can be used to transform
a <a href="../../stl/vector/start.html" class="wikilink1" title="stl:vector:start">vector</a>:
</p>
<pre class="c code c++" style="font-family:monospace;"><span class="kw4">int</span> increment<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> <span class="sy0">++</span>i<span class="sy0">;</span> <span class="br0">}</span>
<span class="kw4">int</span> sum<span class="br0">(</span><span class="kw4">int</span> a<span class="sy0">,</span> <span class="kw4">int</span> b<span class="br0">)</span> <span class="br0">{</span> <span class="kw1">return</span> a<span class="sy0">+</span>b<span class="sy0">;</span> <span class="br0">}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
vector<span class="sy0"><</span>int<span class="sy0">></span> v1<span class="sy0">;</span>
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">int</span> i<span class="sy0">=</span><span class="nu0">1</span><span class="sy0">;</span> i<span class="sy0"><</span><span class="nu0">6</span><span class="sy0">;</span> i<span class="sy0">++</span><span class="br0">)</span> v1.<span class="me1">push_back</span> <span class="br0">(</span>i<span class="sy0">*</span>i<span class="br0">)</span><span class="sy0">;</span> <span class="co1">// v1: 1 4 9 16 25</span>
vector<span class="sy0"><</span>int<span class="sy0">></span> v2<span class="br0">(</span>v1.<span class="me1">size</span><span class="br0">(</span><span class="br0">)</span><span class="br0">)</span><span class="sy0">;</span>
transform<span class="br0">(</span>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> v2.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> increment<span class="br0">)</span><span class="sy0">;</span> <span class="co1">// v2: 2 5 10 17 26</span>
<span class="co1">// add the elements of v1 and v2 together, store the result in v1</span>
transform<span class="br0">(</span>v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> v1.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> v2.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> v1.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy0">,</span> sum<span class="br0">)</span><span class="sy0">;</span> <span class="co1">// v1: 3 9 19 33 51</span>
<span class="kw1">return</span> <span class="nu0">0</span><span class="sy0">;</span>
<span class="br0">}</span></pre>
<p>
Related Topics: <a href="../../stl/algorithm/copy.html" class="wikilink1" title="stl:algorithm:copy">copy</a>, <a href="../../stl/algorithm/fill.html" class="wikilink1" title="stl:algorithm:fill">fill</a>, <a href="../../stl/algorithm/generate.html" class="wikilink1" title="stl:algorithm:generate">generate</a>
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