<refentry id="intercept">
<refnamediv>
<refname>Intercept</refname>
<refpurpose>set function for interrupt processing</refpurpose>
</refnamediv>

<refsynopsisdiv>
<funcsynopsis>
<funcprototype>
  <funcdef><function>intercept</function></funcdef>
    <paramdef>int <parameter>(* func)</parameter>
        <funcparams>int</funcparams></paramdef>
</funcprototype>
</funcsynopsis>

</refsynopsisdiv>

<refsect1><title>Assembler Equivalent</title>
<para>
os9 F$ICPT
</para>
</refsect1>

<refsect1><title>Description</title>
<para>
Intercept instructs OS-9 to pass control to the function "func"
when an interrupt (signal) is received by the current process.
</para>
<para>
If the interrupt processing function has an argument, it will
contain the value of the signal received. On return from
"func", the process resumes at the point in the program where
it was interrupted by the signal. "Interrupt()" is an
alternative to the use of "signal()" to process interrupts.
</para>
<para>
As an example, suppose we wish to ensure that a partially
completed output file is deleted if an interrupt is received.
The body of the program might include:
<programlisting>
char *temp_file = "temp"; /* name of temporary file */
int pn=0;                 /* path number */
int intrupt();            /* predeclaration */

...

intercept(intrupt);       /* route interrupt processing */
pn = creat(temp_file,3);  /* make a new file */

...

write(pn,string,count);   /* write string to temp file */

...

close(pn);
pn=0;

...
</programlisting>
The interrupt routine might be coded:
<programlisting>
intrupt(sig);
{
     if (pn){ /* only done if pn refers to an open file */
          close(pn);
          unlink(temp_file); /* delete */
     }
exit(sig);
}
</programlisting>
</para>
</refsect1>

<refsect1><title>Caveats</title>
<para>
"Intercept()" and "signal()" are mutually incompatible so that
calls to both must not appear in the same program. The linker
guards against this by giving an "entry name clash - _sigint"
error if it is attempted.
</para>
</refsect1>

<refsect1><title>See Also</title>
<para>
<link linkend="signal">signal()</link>
</para>
</refsect1>

</refentry>