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><H1
><A
NAME="REF.IF-DEFINE"><SPAN
CLASS="PROPERTY"
>if_define</SPAN
></H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN4442"
></A
><H2
>Name</H2
>Property <SPAN
CLASS="PROPERTY"
>if_define</SPAN
> -- Output a common preprocessor construct to a configuration
header file.</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN4446"><H2
>Synopsis</H2
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="SYNOPSIS"
>cdl_option <name> {
if_define [-file=<filename>] <symbol1> <symbol2>
…
}</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN4448"
></A
><H2
>Description</H2
><P
>The purpose of the <SPAN
CLASS="PROPERTY"
>if_define</SPAN
> property is best explained by an
example. Suppose you want finer-grained control over assertions, say
on a per-package or even a per-file basis rather than globally. The
assertion macros can be defined by an exported header file in an
infrastructure package, using code like the following:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#ifdef CYGDBG_USE_ASSERTS
# define CYG_ASSERT( _bool_, _msg_ ) \
CYG_MACRO_START \
if ( ! ( _bool_ ) ) \
CYG_ASSERT_DOCALL( _msg_ ); \
CYG_MACRO_END
#else
# define CYG_ASSERT( _bool_, _msg_ ) CYG_EMPTY_STATEMENT
#endif</PRE
></TD
></TR
></TABLE
><P
>Assuming this header file is <TT
CLASS="LITERAL"
>#include'd</TT
> directly or
indirectly by any code which may need to be built with assertions
enabled, the challenge is now to control whether or not
<TT
CLASS="VARNAME"
>CYGDBG_USE_ASSERTS</TT
> is defined for any given source
file. This is the purpose of the <SPAN
CLASS="PROPERTY"
>if_define</SPAN
> property:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_option CYGDBG_KERNEL_USE_ASSERTS {
…
if_define CYGSRC_KERNEL CYGDBG_USE_ASSERTS
requires CYGDBG_INFRA_ASSERTION_SUPPORT
}</PRE
></TD
></TR
></TABLE
><P
>If this option is active and enabled then the kernel's configuration
header file would end up containing the following:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#ifdef CYGSRC_KERNEL
# define CYGDBG_USE_ASSERTS 1
#endif</PRE
></TD
></TR
></TABLE
><P
>Kernel source code can now begin with the following construct:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#define CYGSRC_KERNEL 1
#include <pkgconf/kernel.h>
#include <cyg/infra/cyg_ass.h></PRE
></TD
></TR
></TABLE
><P
>The configuration option only affects kernel source code, assuming
nothing else <TT
CLASS="LITERAL"
>#define's</TT
> the symbol
<TT
CLASS="VARNAME"
>CYGSRC_KERNEL</TT
>. If the per-package assertion option
is disabled then <TT
CLASS="VARNAME"
>CYGDBG_USE_ASSERTS</TT
> will not get
defined. If the option is enabled then
<TT
CLASS="VARNAME"
>CYGDBG_USE_ASSERTS</TT
> will get defined and assertions
will be enabled for the kernel sources. It is possible to use the same
mechanism for other facilities such as tracing, and to apply it at a
finer grain such as individual source files by having multiple options
with <SPAN
CLASS="PROPERTY"
>if_define</SPAN
> properties and multiple symbols such as
<TT
CLASS="VARNAME"
>CYGSRC_KERNEL_SCHED_BITMAP_CXX</TT
>.</P
><P
>The <SPAN
CLASS="PROPERTY"
>if_define</SPAN
> property takes two arguments, both of which must be
valid C preprocessor symbols. If the current option is active and
enabled then three lines will be output to the configuration header
file:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#ifdef <symbol1>
# define <symbol2>
#endif</PRE
></TD
></TR
></TABLE
><P
>If the option is inactive or disabled then these lines will not be
output. By default the current package's configuration header file
will be used, but it is possible to specify an alternative destination
using a <TT
CLASS="LITERAL"
>-file</TT
> option. At present the only
legitimate alternative destination is <TT
CLASS="LITERAL"
>system.h</TT
>, the
global configuration header. <SPAN
CLASS="PROPERTY"
>if_define</SPAN
> processing happens in
addition to, not instead of, the normal <TT
CLASS="LITERAL"
>#define</TT
>
processing or the handling of other header-file related properties.</P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>The infrastructure in the current <SPAN
CLASS="APPLICATION"
>eCos</SPAN
> release does not yet work
this way. In future it may do so, and the intention is that suitable
configuration options get generated semi-automatically by the
configuration system rather than having to be defined explicitly.</P
></BLOCKQUOTE
></DIV
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>As an alternative to changing the configuration, updating the build
tree, and so on, it is possible to enable assertions by editing a
source file directly, for example:</P
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>#define CYGSRC_KERNEL 1
#define CYGDBG_USE_ASSERTS 1
#include <pkgconf/kernel.h>
#include <cyg/infra/cyg_ass.h></PRE
></TD
></TR
></TABLE
><P
>The assertion header file does not care whether
<TT
CLASS="VARNAME"
>CYGDBG_USE_ASSERTS</TT
> is <TT
CLASS="LITERAL"
>#define'd</TT
>
via a configuration option or by explicit code. This technique can be
useful to component writers when debugging their source code, although
care has to be taken to remove any such <TT
CLASS="LITERAL"
>#define's</TT
>
later on.</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN4487"
></A
><H2
>Example</H2
><TABLE
BORDER="5"
BGCOLOR="#E0E0F0"
WIDTH="70%"
><TR
><TD
><PRE
CLASS="PROGRAMLISTING"
>cdl_option CYGDBG_KERNEL_USE_ASSERTS {
display "Assertions in the kernel package"
…
if_define CYGSRC_KERNEL CYGDBG_USE_ASSERTS
requires CYGDBG_INFRA_ASSERTION_SUPPORT
}</PRE
></TD
></TR
></TABLE
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN4490"
></A
><H2
>See Also</H2
><P
>Properties <A
HREF="ref.define.html"
><SPAN
CLASS="PROPERTY"
>define</SPAN
></A
>,
<A
HREF="ref.define-format.html"
><SPAN
CLASS="PROPERTY"
>define_format</SPAN
></A
>,
<A
HREF="ref.define-header.html"
><SPAN
CLASS="PROPERTY"
>define_header</SPAN
></A
>,
<A
HREF="ref.define-proc.html"
><SPAN
CLASS="PROPERTY"
>define_proc</SPAN
></A
> and
<A
HREF="ref.no-define.html"
><SPAN
CLASS="PROPERTY"
>no_define</SPAN
></A
>.</P
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