Define host variables based on C #defines and typedefs

When the C preprocessor runs on a source file, it expands the contents of all C header files where they are included within the source file. This expansion makes it possible to use host variables in IBM® Informix® ESQL/C source files based on types and #define and typedef statements in C header files. The examples given here indicate some of the advantages of sharing header files. In the following example, the same C header file is used by both Informix ESQL/C and C source files.

Figure 1. ESQL/C and C excerpt that share a C header file

/*header file i.h*/
#define LEN 15
typedef struct customer_t{
   int    c_no;
   char   fname[LEN];
   char   lname[LEN];
   } CUST_REC;
⋮

/*cust.ec*/
#include <stdio.h>

EXEC SQL BEGIN DECLARE SECTION;
#include "i.h"
EXEC SQL END DECLARE SECTION;

int main()
{

EXEC SQL BEGIN DECLARE SECTION;
   CUST_REC cust;
EXEC SQL END DECLARE SECTION;
⋮

}


/*name.c*/
#include “i.h”
int main ()
{...
   CUST_REC cust;
⋮

}

In the following example, the Informix ESQL/C source file contains a host variable based on a type defined in the time.h system-header file.

Figure 2. ESQL/C excerpt that uses a host variable of the type defined in a C system-header file

/*time.ec*/

#include <time.h>

main ()
{...
EXEC SQL BEGIN DECLARE SECTION;
    time_t time_hostvar;
EXEC SQL END DECLARE SECTION;
⋮

}

A C header file can be included anywhere inside the Informix ESQL/C source file. However, to define host variables in Informix ESQL/C files based on #defines and typedefs defined in C header files, you must include the C header file within the EXEC SQL declare section.

Contrast the example in Figure 3, which leads to error -33051: Syntax error on identifier or symbol ‘name_hostvar with the example in Figure 1 which does not. The only difference is that in the example in Figure 1, the C header file with the #define and the typedef that is used in the EXEC SQL declare section is included within that declare section.

Figure 3. ESQL/C excerpt that defines a host variable based on a c header file included outside the declare section

/*header file i.h*/
#define LEN 15
typedef struct customer_t{
   int    c_no;
   char   fname[LEN];
   char   lname[LEN];
   } CUST_REC;
⋮

/*cust.ec*/
#include "i.h"

int main()
{

EXEC SQL BEGIN DECLARE SECTION;
   CUST_REC cust;
⋮

}
⋮

...Leads to error -33051...