Re: Pragma Interface "C"

From: Thomas Kyte <tkyte_at_us.oracle.com>
Date: 1997/07/08
Message-ID: <33c3766d.14047999_at_newshost>#1/1

On 8 Jul 1997 16:00:19 GMT, matt_at_beaker.imicro.com (Matthew Benjamin) wrote:

>I heard somewhere that it was possible to use the (Ada-derived)
>PRAGMA INTERFACE "C" directive to declare external C functions, which
>would presumably reside in external libraries on an Oracle server
>system.
>
>I have not seen any official or unofficial Oracle documentation which
>explains how one would do this.
>
The pragma interface "C" is an internal mechanism and is not exposed for developers to use in the 7.x database. pragma interface "C" can only be used to call c routines in the Oracle Kernel and only under special circumstances. For example, if you ever accidently run the dbms_pipe package in a non SYS schema, you'll find the pragma interfaces stop working (only sys can use it, and only for functions exported from the kernel)

>Similarly, a recent review of Oracle 8/NCA states that Oracle "now" supports
>"C callouts" (the same mechanism?), but again, no reference was given for this claim.
>

This is documented in the pl/sql reference for Oracle8. Here is a real small example:

CREATE FUNCTION gcd (
-- find greatest common divisor of x and y

   x BINARY_INTEGER,
   y BINARY_INTEGER)
RETURN BINARY_INTEGER AS EXTERNAL
   LIBRARY c_utils
   NAME "c_gcd" -- quotes preserve lower case    LANGUAGE C; The C prototype for c_gcd follows:

sb4 c_gcd(sb4 x_val, sb4 y_val);

You have control over how datatypes and such are mapped as well. A more complex example would be:

CREATE FUNCTION parse (

   x IN BINARY_INTEGER,
   Y IN OUT CHAR)
RETURN CHAR AS EXTERNAL
   LIBRARY c_utils
   NAME "c_parse"
   LANGUAGE C
   CALLING STANDARD PASCAL
   PARAMETERS (

      x,            -- stores value of x
      x INDICATOR,  -- stores null status of x
      y,            -- stores value of y
      y LENGTH,     -- stores current length of y
      y MAXLEN,     -- stores maximum length of y
      RETURN INDICATOR);

With this PARAMETERS clause, the C prototype becomes

char * c_parse(sb4 *x, sb2 x_ind, char *y, sb4 *y_len,

                  sb4 *y_maxlen, sb2 *retind);

>Can anyone point me to some information?
>
>
>TIA,
>
>
>Matt Benjamin
>matt_at_imi.imicro.com

Thomas Kyte
tkyte_at_us.oracle.com
Oracle Government
Bethesda MD

http://govt.us.oracle.com/ -- downloadable utilities

---

Opinions are mine and do not necessarily reflect those of Oracle Corporation Received on Tue Jul 08 1997 - 00:00:00 CEST