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62<h1><a class="anchor" name="itfile">Writing and reading data from files </a></h1>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>
63<div class="fragment"><pre class="fragment"><span class="preprocessor">#include &lt;itpp/itcomm.h&gt;</span>
64
65<span class="keyword">using namespace </span>itpp;
66
67<span class="keywordtype">int</span> main() {
68        <span class="comment">// Declare the it_file class</span>
69        it_file ff;
70
71        <span class="comment">// Open a file with the name "it_file_test.it"</span>
72        ff.open ( <span class="stringliteral">"it_file_test.it"</span> );
73
74        <span class="comment">// Create some data to put into the file</span>
75        vec a = linspace ( 1, 20, 20 );
76
77        <span class="comment">// Put the variable a into the file. The Name("a") tells the file class</span>
78        <span class="comment">// that the next variable shall be named "a".</span>
79        ff &lt;&lt; Name ( <span class="stringliteral">"a"</span> ) &lt;&lt; a;
80
81        <span class="comment">// Force the file to be written to disc. This is useful when performing</span>
82        <span class="comment">// iterations and ensures that the information is not stored in any cache</span>
83        <span class="comment">// memory. In this simple example it is not necessary to flush the file.</span>
84        ff.flush();
85
86        <span class="comment">// Close the file</span>
87        ff.close();
88
89        <span class="comment">// Exit program</span>
90        <span class="keywordflow">return</span> 0;
91}
92</pre></div><p>
93When 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>
94<div class="fragment"><pre class="fragment">itload(<span class="stringliteral">'it_file_test.it'</span>)
95figure(1); clf;
96plot(a)
97</pre></div><p>
98Note: 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>
99The IT++ program <code>read_it_file.cpp</code> that reads the file and prints its content can look like this:<p>
100<div class="fragment"><pre class="fragment"></pre></div><p>
101Here is the output of the program:<p>
102<div class="fragment"><pre class="fragment">
103a = [1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20]
104</pre></div> </div>
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