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<?xml version="1.0" encoding="UTF-8"?>
<refentry version="5.0-subset Scilab" xml:id="try" xml:lang="en"
xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:svg="http://www.w3.org/2000/svg"
xmlns:ns5="http://www.w3.org/1999/xhtml"
xmlns:mml="http://www.w3.org/1998/Math/MathML"
xmlns:db="http://docbook.org/ns/docbook">
<info>
<pubdate>$LastChangedDate$</pubdate>
</info>
<refnamediv>
<refname>try</refname>
<refpurpose>beginning of try block in try-catch control
instruction</refpurpose>
</refnamediv>
<refnamediv xml:id="catch">
<refname>catch</refname>
<refpurpose>beginning of catch block in try-catch control
instruction</refpurpose>
</refnamediv>
<refsynopsisdiv>
<title>Calling Sequence</title>
<synopsis>try
statements
catch
statements
end</synopsis>
</refsynopsisdiv>
<refsection>
<title>Description</title>
<para>The <literal>try</literal>-<literal>catch</literal> control
instruction can be used to manage codes that could possibly generate
errors.</para>
<para>When a <literal>try</literal>-<literal>catch</literal> control
instruction is executed, normally only the statements between the
<literal>try</literal> and <literal>catch</literal> keywords are executed.
However, if an error occurs during execution of any of these statements,
the error is recorded, the remaining statements up to the
<literal>catch</literal> keyword are skipped and the statements between
the <literal>catch</literal> and <literal>end</literal> keywords are
executed using the default error handling mode (see <link
linkend="errcatch">errcatch</link>).</para>
<para>The recorded error can be retreived using the <link
linkend="lasterror">lasterror</link> function.</para>
<para>The <literal>catch</literal> statements as well as the
<literal>catch</literal> keyword can be omitted if no alternative
statements are given.</para>
<para>Note that one can also use the <link
linkend="execstr">execstr</link> function with
<literal>'errcatch'</literal> argument for error handling. This can be
particularly useful for handling syntactical errors.</para>
<para>Note also that <literal>try-catch</literal> is more or less similar
to:</para>
<programlisting role = ""><![CDATA[
if execstr("<try instructions>","errcatch")<>0 then
<catch instructions>
end
]]></programlisting>
<para>It uses the same internal mechanism as <link
linkend="errcatch">errcatch</link>. It is the reason why <link
linkend="errcatch">errcatch</link> or
<emphasis>execstr(...,"errcatch")</emphasis> cannot be included in
<literal>try</literal>-<literal>catch</literal> control structures. This
context is detected and produces a specific error message (this error is
catched and stored like any other error if it is triggered in the
<literal>try</literal> block).</para>
<para>However, <literal>try</literal>-<literal>catch</literal> control
structures can be nested (see example 2 below).</para>
</refsection>
<refsection>
<title>Examples</title>
<programlisting role="example"><![CDATA[
// example 1
file_path=TMPDIR+'/wrong'
try
u=mopen(file_path,'r')
x=mget(10,'c',u)
catch
disp(['file '+file_path+ 'cannot be read',
'using default values for x'])
x=1:10
end
[error_message,error_number]=lasterror(%t)
// example 2 (nested try/catch structures)
function nestedtry(a,b)
disp("START")
mprintf("\ta is %s\t\tb is %s\n",string(a),string(b))
try
disp("try 1")
try
disp("try 2")
z=a+1; // err when string
catch
disp("catch 2")
t=b+1; // err when string
end
disp("after try 2")
catch
disp("catch 1")
end
disp("after try 1 - THE END")
endfunction
nestedtry(1,1)
nestedtry("a string",1)
nestedtry(1,"a string")
nestedtry("a string","a string")
]]></programlisting>
</refsection>
<refsection>
<title>See Also</title>
<simplelist type="inline">
<member><link linkend="error">error</link></member>
<member><link linkend="execstr">execstr</link></member>
<member><link linkend="if">if</link></member>
<member><link linkend="lasterror">lasterror</link></member>
<member><link linkend="errcatch">errcatch</link></member>
</simplelist>
</refsection>
<refsection>
<title>Authors</title>
<para>Serge Steer, INRIA</para>
</refsection>
</refentry>
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