To include an external file into your embedded SQL program, use:
EXEC SQL INCLUDE filename
;
The embedded SQL preprocessor will look for a file named
,
preprocess it, and include it in the resulting C output. Thus,
embedded SQL statements in the included file are handled correctly.
filename
.h
Note that this is not the same as
#include <filename
.h>
because this file would not be subject to SQL command preprocessing.
Naturally, you can continue to use the C
#include
directive to include other header
files.
The include file name is case-sensitive, even though the rest of
the EXEC SQL INCLUDE
command follows the normal
SQL case-sensitivity rules.
Similar to the directive #define
that is known from C,
embedded SQL has a similar concept:
EXEC SQL DEFINEname
; EXEC SQL DEFINEname
value
;
So you can define a name:
EXEC SQL DEFINE HAVE_FEATURE;
And you can also define constants:
EXEC SQL DEFINE MYNUMBER 12; EXEC SQL DEFINE MYSTRING 'abc';
Use undef
to remove a previous definition:
EXEC SQL UNDEF MYNUMBER;
Of course you can continue to use the C versions #define
and #undef
in your embedded SQL program. The difference
is where your defined values get evaluated. If you use EXEC SQL
DEFINE
then the ecpg preprocessor evaluates the defines and substitutes
the values. For example if you write:
EXEC SQL DEFINE MYNUMBER 12; ... EXEC SQL UPDATE Tbl SET col = MYNUMBER;
then ecpg will already do the substitution and your C compiler will never
see any name or identifier MYNUMBER
. Note that you can not use
#define
for a constant that you are going to use in an
embedded SQL query because in this case the embedded SQL precompiler is not
able to see this declaration.
You can use the following directives to compile code sections conditionally:
EXEC SQL ifdef name
;
Checks a name
and processes subsequent lines if
name
has been created with EXEC SQL define
.
name
EXEC SQL ifndef name
;
Checks a name
and processes subsequent lines if
name
has not been created with
EXEC SQL define
.
name
EXEC SQL else;
Starts processing an alternative section to a section introduced by
either EXEC SQL ifdef
or
name
EXEC SQL ifndef
.
name
EXEC SQL elif name
;
Checks name
and starts an alternative section if
name
has been created with EXEC SQL define
.
name
EXEC SQL endif;
Ends an alternative section.
Example:
exec sql ifndef TZVAR; exec sql SET TIMEZONE TO 'GMT'; exec sql elif TZNAME; exec sql SET TIMEZONE TO TZNAME; exec sql else; exec sql SET TIMEZONE TO TZVAR; exec sql endif;