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<div class="title">TRY-CATCH Try and Catch Statement </div> </div>
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<div class="textblock"><p>Section: <a class="el" href="sec_flow.html">Flow Control</a> </p>
<h1><a class="anchor" id="Usage"></a>
Usage</h1>
<p>The <code>try</code> and <code>catch</code> statements are used for error handling and control. A concept present in <code>C++</code>, the <code>try</code> and <code>catch</code> statements are used with two statement blocks as follows </p>
<pre class="fragment"> try
statements_1
catch
statements_2
end
</pre><p> The meaning of this construction is: try to execute <code>statements_1</code>, and if any errors occur during the execution, then execute the code in <code>statements_2</code>. An error can either be a FreeMat generated error (such as a syntax error in the use of a built in function), or an error raised with the <code>error</code> command. </p>
<h1><a class="anchor" id="Examples"></a>
Examples</h1>
<p>Here is an example of a function that uses error control via <code>try</code> and <code>catch</code> to check for failures in <code>fopen</code>.</p>
<pre class="fragment"> read_file.m
</pre><pre class="fragment">function c = read_file(filename)
try
fp = fopen(filename,'r');
c = fgetline(fp);
fclose(fp);
catch
c = ['could not open file because of error :' lasterr]
end
</pre><p>Now we try it on an example file - first one that does not exist, and then on one that we create (so that we know it exists).</p>
<pre class="fragment">--> read_file('this_filename_is_invalid')
c =
could not open file because of error :Invalid handle!
ans =
could not open file because of error :Invalid handle!
--> fp = fopen('test_text.txt','w');
--> fprintf(fp,'a line of text\n');
--> fclose(fp);
--> read_file('test_text.txt')
ans =
a line of text
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