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67<h1><a class="anchor" id="itfile">Writing and reading data from files </a></h1><p>Here we will use the <code>it_file</code> class to store some data. The program <code>write_it_file.cpp</code> looks as follows:</p>
68<div class="fragment"><pre class="fragment"><span class="preprocessor">#include &lt;itpp/itcomm.h&gt;</span>
69
70<span class="keyword">using namespace </span>itpp;
71
72<span class="keywordtype">int</span> main() {
73        <span class="comment">// Declare the it_file class</span>
74        it_file ff;
75
76        <span class="comment">// Open a file with the name &quot;it_file_test.it&quot;</span>
77        ff.open ( <span class="stringliteral">&quot;it_file_test.it&quot;</span> );
78
79        <span class="comment">// Create some data to put into the file</span>
80        vec a = linspace ( 1, 20, 20 );
81
82        <span class="comment">// Put the variable a into the file. The Name(&quot;a&quot;) tells the file class</span>
83        <span class="comment">// that the next variable shall be named &quot;a&quot;.</span>
84        ff &lt;&lt; Name ( <span class="stringliteral">&quot;a&quot;</span> ) &lt;&lt; a;
85
86        <span class="comment">// Force the file to be written to disc. This is useful when performing</span>
87        <span class="comment">// iterations and ensures that the information is not stored in any cache</span>
88        <span class="comment">// memory. In this simple example it is not necessary to flush the file.</span>
89        ff.flush();
90
91        <span class="comment">// Close the file</span>
92        ff.close();
93
94        <span class="comment">// Exit program</span>
95        <span class="keywordflow">return</span> 0;
96}
97</pre></div><p>When you run this program you will obtain a file called <code>it_file_test.it</code> in your current directory. You can read the file into Matlab/Octave to view the data by using the following commands:</p>
98<div class="fragment"><pre class="fragment">itload(<span class="stringliteral">&apos;it_file_test.it&apos;</span>)
99figure(1); clf;
100plot(a)
101</pre></div><p>Note: Make sure that <code>$PREFIX/share/itpp</code> is in your Matlab/Octave path and that you run the code above from the directory where <code>it_file_test.it</code> is located (<code>$PREFIX</code> is the IT++ installation prefix; <code>/usr/local</code> by default).</p>
102<p>The IT++ program <code>read_it_file.cpp</code> that reads the file and prints its content can look like this:</p>
103<div class="fragment"><pre class="fragment"></pre></div><p>Here is the output of the program:</p>
104<div class="fragment"><pre class="fragment">
105a = [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20]
106</pre></div> </div>
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