Calling external proceedures

Question

I try make the external routine writen in C. Function writen in C and stored in D:\extproc\zzz1.dll
I make the library and function
CREATE or replace LIBRARY externProcedures AS 'D:\extproc\zzz1.dll'
create or replace function pls_max(x binary_integer)
return binary_integer as
external library externProcedures
name "find_max" language C parameters (x long);
Then i execute SQl: select pls_max(10) from dual;
And got the error
ERROR at line 1:
ORA-06521: PL/SQL: Error mapping function
ORA-06522: Unable to load symbol from DLL
Anyone have any idea how to solve this problem? Iv heard about using the following code
#ifdef __cplusplus
extern "C" {
#endif
and
#ifdef __cplusplus
#endif
around the external function. But to be honest this confuses me more. What external function and how does it go around it?
For the sake of my sanity, does anyone have any ideas?
Kind Regards
Richard Clayton

Answer 1

hi i am ashutosh i am too having a similar kind of problem
this is what i did
MY CPP FILE
# include <conio.h>
# include <stdio.h>
#include "dlltest.h"
#define MAXMODULE 50
char module[MAXMODULE];
extern "C" __declspec(dllexport) int NumberList()
{       //GetModuleFileName(NULL, (LPTSTR)module, MAXMODULE);      
printf("\n\nThis function was called from ");
          printf("NumberList(): ");
          for(int i=0; i<10; i++)
          {      printf("%d ",i);
          printf("\n\n");
          return int(10);
extern "C" __declspec(dllexport) int LetterList(int x)
{       //GetModuleFileName(NULL, (LPTSTR)module, MAXMODULE);      
printf("\n\nThis function was called from ");
          printf("LetterList(): ");
for(int i=0; i<26; i++)
     {       printf("%c ",char(97 + i));
} printf("\n\n");
     return 10;
HEADER FILE
#ifdef __cplusplus
extern "C" {
#endif
extern "C" __declspec(dllexport) int NumberList();
//int NumberList();
#ifdef __cplusplus
#endif
#ifndef DLLTESTH_
#define DLLTESTH_
#include <iostream.h>
#include <stdio.h>
#include <windows.h>
extern "C" __declspec(dllexport) int LetterList(int);
#endif
NOW I WANT TO CALL THE NumberList FUNCTION IN MYDLL.DLL FILE FROM ORACLE
SO THIS IS WHT I DID
CREATE OR REPLACE LIBRARY nt_kernel
AS
--'c:\winnt\system32\MYDLL.dll';
'E:\DLL\MyDLL\Debug\MYDLL.dll';
CREATE OR REPLACE PACKAGE disk_util
AS
FUNCTION get_disk_free_space
-- (X OUT PLS_INTEGER)
RETURN PLS_INTEGER;
PRAGMA RESTRICT_REFERENCES (get_disk_free_space,WNPS, RNPS, WNDS, RNDS);
END disk_util;
CREATE OR REPLACE PACKAGE BODY disk_util
AS
FUNCTION get_disk_free_space
--(X OUT PLS_INTEGER)
RETURN PLS_INTEGER
IS EXTERNAL
LIBRARY nt_kernel -- our library (defined previously)
NAME "NumberList" -- name of function in kernel32.dll
LANGUAGE C -- external routine is written in C
CALLING STANDARD PASCAL -- uses Pascal parameter convention
PARAMETERS -- map PL/SQL to C parameters by
-- position
(RETURN int);
END disk_util;
CREATE OR REPLACE PROCEDURE TEMP
AS
lX PLS_INTEGER;
return_code PLS_INTEGER;
BEGIN
return_code := disk_util.get_disk_free_space ();
DBMS_OUTPUT.PUT_LINE('free disk space, megabytes = ' || to_char(return_code));
END;
*********WHEN I EXEC TEMP THE FOLLOWING ERROR SHOWED UP
SQL> EXEC TEMP;
BEGIN TEMP; END;
ERROR at line 1:
ORA-06521: PL/SQL: Error mapping function
ORA-06522: Unable to load symbol from DLL
ORA-06512: at "MNE.DISK_UTIL", line 0
ORA-06512: at "MNE.TEMP", line 6
ORA-06512: at line 1