Problem with external procedure

Question

Please,
i'm doing some experiments in Microsoft Win2003 environment calling a c function as external procedures.
I've build a sample using Dev-C++ that make a DLL (i don't know c language) named sysDLL.dll
DllClass::DllClass(char *cmd)
int num;
num = system(cmd);
I need only to execute some OS command from PL/SQL (rdbms 10.2).
I've putted DLL in $ORACLE_HOME\bin.
Then I've created library with this statement :
Create Library scott.c_sysdll as 'C:\oracle\product\10.2.0\db_3\bin\sysdll.dll'
and at the end I've created the procedure :
create or replace procedure scott.shell(cmd IN varchar2)
as language C
library c_SysDll
name "DllClass"
parameters (cmd string);
But when I execute this procedure from sql*plus I've always get :
ORA-06521: PL/SQL: Error mapping function
ORA-06522: Unable to load symbol from DLL
ORA-06512: at "SCOTT.SHELL", line 1
ORA-06512: at line 1
Please help me, thanks !

Answer 1

Suggest that you first make it much simpler. Do not object orientation. Use plain vanilla flavour C. And even before using C, use a kernel call instead. For example, the gethostname() is a standard Socket call that you will find on many operating system (including Windows & Unix).
The following code sample illustrates (can be run as is via SQL*Plus):<font color="blue">
-- specify the external library (shared lib on Unix, DLL on Windows)
create or replace library libc as 'libc.sl';
-- The kernel call that we're going to wrap with a PL/SQL function:
--      int gethostname(char *hostname, size_t size);
-- wrapping this API call with a PL/SQL function
create or replace function gethostname( hostname OUT string, size_t binary_integer ) return binary_integer is
        external
        library libc
        name "gethostname"
        language C
        calling standard C
        parameters
                hostname        STRING,
                size_t          INT
-- calling the kernel API routine from within PL/SQL
set serveroutput on
declare
        host$   varchar2(60);
        rc$     integer;
begin
        rc$ := gethostname( host$, 60 );
        dbms_output.put_line( 'hostname is ['|| host$ ||'] return code=['|| TO_CHAR(rc$) || ']' );
end;
/</font>
<p>
Of course, the DLL name for Window is different than the Shared Library ('libc.sl') used in the above snippet. Do not have a Win32 Oracle platform to test on, but you should find this API call in the winsock.dll library.
<p>
As for writing your custom extproc in C. Plain vanilla C is something as follows:
int dosomestuff()
  return( 123456 );
<p>
Remember that this function has to be exported in the DLL interface.
<p>
Also keep in mind that using extproc is usually the last option to pursue when dealing with Oracle development. The basic rules are as follows:
1. Do it in SQL.
2. If it cannot be done in SQL, do it as a PL/SQL proc
3. If if cannot be done in PL/SQL. do it as a Java stored proc
4. If if cannot be done in Java, do is as an external proc<p>
The times that I need to resort to using Java is less than a handful (most obvious one is using Java to gain o/s command line access). I have never put external proc code into production as we have yet to have a need for something so exceptional, that it cannot be done using SQL, PL/SQL or Java as the last resort.