Function parameters as host variables

You can use host variables as parameters to functions. You must precede the name of the host variable with the parameter keyword to declare it as a function parameter.

For example, the following figure shows a code fragment with a Kernighan and Ritchie-style prototype declaration that expects three parameters, two of which are host variables.

Figure 1: Using EXEC SQL to declare host variables as parameters to a Kernighan and Ritchie-Style function declaration

f(s, id, s_size)
EXEC SQL BEGIN DECLARE SECTION;
   PARAMETER char s[20];
   PARAMETER int id;
EXEC SQL END DECLARE SECTION;
int s_size;
{
   select fname into :s from customer 
      where customer_num = :id;


}

You can also declare parameter host variables with the dollar sign ($) notation. For example, the following figure shows the function header in Using EXEC SQL to declare host variables as parameters to a Kernighan and Ritchie-Style function declaration, with the dollar sign ($) notation.

Figure 2: Using the dollar sign ($) to declare host variables as parameters to a function

f(s, id, s_size)
$parameter char s[20];
$parameter int id;
int s_size;

You can declare parameters in an ANSI-style prototype function declaration as host variables as well. You can also put all parameters to a prototype function declaration inside the EXEC SQL declare section, even if some of the parameters cannot be used as host variables. The following figure shows that the function pointer f can be included in the EXEC SQL declare section, even though it is not a valid host-variable type and cannot be used as a host variable.

Figure 3: Using EXEC SQL to declare host variables as parameters to ANSI-style function declaration

int * foo(
EXEC SQL BEGIN DECLARE SECTION;
   PARAMETER char s[20],
   PARAMETER int id,
   PARAMETER int (*f) (double)
EXEC SQL END DECLARE SECTION;
)
{
   select fname into :s from customer 
      where customer_num = :id;


}

The functionality that allows inclusion of function parameters inside of the EXEC SQL declare section is in compliance with the requirement that any valid C declaration syntax must be allowed inside the EXEC SQL declare sections to use common header files for C and Informix® ESQL/C source files. For more information about how to use common header files between C and Informix ESQL/C source files, see ids_esqlc_0091.html#ids_esqlc_0091.

Important: If you want to define Informix ESQL/C host variables that are ANSI-style parameters, you must use the EXEC SQL BEGIN DECLARE SECTION and the EXEC SQL END DECLARE SECTION syntax. You cannot use the $BEGIN DECLARE and $END DECLARE syntax. This restriction is because SQL statements that begin with the dollar sign ($) notion must end with a semicolon (;). However, ANSI syntax requires that each parameter in a parameter list does not end with a semicolon terminator, but with a comma (,) delimiter.

The following limitations apply to using host variables as function parameters:

You cannot declare a parameter variable inside a block of C code.
You cannot use the parameter keyword in declarations of host variables that are not part of a function header. If you do, you receive unpredictable results.