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From: hpe@cs.hut.fi (Hannu Peltonen)
Newsgroups: comp.databases
Subject: Re: Informix ESQL/C with C++
Message-ID: <HPE.91Apr25101227@hutcs.hut.fi>
Date: 25 Apr 91 08:12:27 GMT
References: <741@strengur.is>
Sender: news@santra.uucp (Cnews - USENET news system)
Organization: Helsinki University of Technology, Finland
Lines: 118
In-Reply-To: snorri@strengur.is's message of 24 Apr 91 17:50:58 GMT

We use Informix 4.0 OnLine ESQL with HP C++ 2.0 (i.e., AT&T 2.0
cfront).  We have written a header file that declares both the
functions to be called by the application programmer and the functions
called from the code generated by the preprocessor.

The list of preprocessor functions may not be complete; we have added
functions as we have encountered them in the generated code.

To compile a C++ program with embedded SQL, we use a simple command
script.  The script removes C++ style comments ("// xxxxx"), which
confuse the Informix preprocessor, runs the preprocessor, and finally
compiles the C++ program.

This has worked fine.  Note that if a parameter of a function is to be
used as an Informix host variable, one has to declare an extra variable.
For example:

	void f (int n)
	{
	  $ int nn = n;
	  $ select ... where x = $n;
	  ...
	}

As a small detail, which has nothing to do with C++, we have noticed
that the Informix "$include" statement fails to add a "#line" directive
after the lines it has inserted.  This means that the error messages
from C or C++ compiler between the "$include" statement and the next
ESQL statement have invalid line numbers.  This problem can be avoided
simply by writing

	#include <sqlca.h>

instead of

	$ include sqlca;

We have not written any "real" C++ interface which could perhaps
represent tables as classes.

The header file is as follows:

------------------ BEGIN HEADER FILE ---------------------------------------

#ifndef _informix_
#define _informix_

#include <time.h>
#ifndef TU_YEAR
#include <datetime.h>
#endif

extern "C" {
  int	bycmpr (const char *, const char *, int);
  void	bycopy (const char *, char *, int);
  void	byfill (char *, int, char);
  int	byleng (const char *, int);
  void	ldchar (const char *, char *, int);
  void	rdownshift (char *);
  int	rgetmsg (short, char *, short);
  int	risnull (int, const char *);
  void	rsetnull (int, char *);
  int	rstod (const char *, double *);
  int	rstoi (const char *, int *);
  int	rstol (const char *, long *);
  int	rtypalign (int, int);
  int	rtypmsize (int, int);
  const char	*rtypname (int);
  int	rtypwidth (int, int);
  void	rupshift (char *);
  void	sqlbreak ();
  void	sqlexit ();
  void	sqlstart ();
  void	stcat (const char *, char *);
  void	stchar (const char *, char *, int);
  int	stcmpr (const char *, const char *);
  void	stcopy (const char *, char *);
  int	stleng (const char *);

  void	dtcurrent (dtime_t *);
  int	dtcvasc (const char *, dtime_t *);
  int	dtextend (const dtime_t *, dtime_t *);
  void	dttoasc (const dtime_t *, char *);
  int	incvasc (const char *, intrvl_t *);
  int	intoasc (const intrvl_t *, char *);

// The following functions are called from the code generated by the
// Informix precompiler.

  void	_iqdclcur (...);
  void	_iqcopen (...);
  void	_iqnftch (...);
  void	_iqclose (...);
  void	_iqdatabase (...);
  void  _iqslct (...);
  void	_iqprepare (...);
  void	_iqdscribe (...);
  void	_iqddclcur (...);
  void	_iqfree (...);
  void	_iqstmnt (...);
  void	_iqeximm (...);
  void	_iqbeginwork (...);
  void	_iqcommit (...);
  void	_iqrollback (...);
  void	_iqxecute (...);
}

#endif

-------------------- END HEADER FILE -----------------------------------------
--

-------------------------------------------------------------------------
 Hannu Peltonen                             Telephone : +358-0-451 3244
 Helsinki University of Technology          FAX       : +358-0-451 3293
 Department of Computer Science             Internet  : hpe@cs.hut.fi
 Otakaari 1, SF-02150 Espoo, FINLAND
-------------------------------------------------------------------------