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<TITLE>CLN, a Class Library for Numbers - 12. Customizing</TITLE>
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<H1><A NAME="SEC68" HREF="cln_toc.html#TOC68">12. Customizing</A></H1>


<H2><A NAME="SEC69" HREF="cln_toc.html#TOC69">12.1 Error handling</A></H2>

<P>
When a fatal error occurs, an error message is output to the standard error
output stream, and the function <CODE>cl_abort</CODE> is called. The default
version of this function (provided in the library) terminates the application.
To catch such a fatal error, you need to define the function <CODE>cl_abort</CODE>
yourself, with the prototype

<PRE>
#include &#60;cl_abort.h&#62;
void cl_abort (void);
</PRE>

<P>
This function must not return control to its caller.


<H2><A NAME="SEC70" HREF="cln_toc.html#TOC70">12.2 Floating-point underflow</A></H2>

<P>
Floating point underflow denotes the situation when a floating-point number
is to be created which is so close to <CODE>0</CODE> that its exponent is too
low to be represented internally. By default, this causes a fatal error.
If you set the global variable

<PRE>
cl_boolean cl_inhibit_floating_point_underflow
</PRE>

<P>
to <CODE>cl_true</CODE>, the error will be inhibited, and a floating-point zero
will be generated instead.
The default value of <CODE>cl_inhibit_floating_point_underflow</CODE> is
<CODE>cl_false</CODE>.


<H2><A NAME="SEC71" HREF="cln_toc.html#TOC71">12.3 Customizing I/O</A></H2>

<P>
The output of the function <CODE>fprint</CODE> may be customized by changing the
value of the global variable <CODE>cl_default_print_flags</CODE>.


<H2><A NAME="SEC72" HREF="cln_toc.html#TOC72">12.4 Customizing the memory allocator</A></H2>

<P>
Every memory allocation of CLN is done through the function pointer
<CODE>cl_malloc_hook</CODE>. Freeing of this memory is done through the function
pointer <CODE>cl_free_hook</CODE>. The default versions of these functions,
provided in the library, call <CODE>malloc</CODE> and <CODE>free</CODE> and check
the <CODE>malloc</CODE> result against <CODE>NULL</CODE>.
If you want to provide another memory allocator, you need to define
the variables <CODE>cl_malloc_hook</CODE> and <CODE>cl_free_hook</CODE> yourself,
like this:

<PRE>
#include &#60;cl_malloc.h&#62;
void* (*cl_malloc_hook) (size_t size) = ...;
void (*cl_free_hook) (void* ptr)      = ...;
</PRE>

<P>
The <CODE>cl_malloc_hook</CODE> function must not return a <CODE>NULL</CODE> pointer.


<P>
It is not possible to change the memory allocator at runtime, because
it is already called at program startup by the constructors of some
global variables.


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