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This API is expecting the parameters to be passed by reference (a pointer
to the value) as opposed to by value. While the C prototype does have:
void QLGCNVCS(char *,
char *,
char *,
long,
char *);
the header file qsysinc/h.qlgcnvcs also has :
#pragma linkage(QLGCNVCS,OS,nowiden)
which causes the C compiler to pass arguments using the operating system
(OS) convention -- pass by reference. What happens in this particular case
is the integer (long) is copied to a temporary location and a pointer to
this temporary is passed to the API.
In general if you see APIs documented in the style:
-----------------------------
Required Parameter Group:
1 Some variable Input
Char(*)
.....
-----------------------------
the API is expecting pointers to the variables.
If on the other hand you see this style of documentation:
-----------------------------
Syntax
#include<something.h>
int ApiName (int SomeVariable, ...
-----------------------------
then the API is expecting value arguments for ints, etc.
Bruce Vining
Vernon Hamberg
<vhamberg@comcast
.net> To
Sent by: Midrange Systems Technical
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s@xxxxxxxxxxxx <midrange-l@xxxxxxxxxxxx>
cc
05/17/2005 10:35 Subject
PM Re: QLGCNVCS problems with V5R3
Please respond to
Midrange Systems
Technical
Discussion
Peter
I hope to believe that this is a common error - at least the 2 of us have
made a similar mistake in the past, and 2 is more common than 1, eh?
The issue is that everything in CL (before V5R3) uses pointers for passing
parameters. Many of the APIs want you to send them an integer, say, as in
this case, and have it sent as the real value, not as a pointer to the
value. That means you cannot use this API safely in CL before V5R3. If I
read the docs right, you are actually sending the first 4 bytes of a
pointer.
The thing to watch for in the API doc is for an asterisk in parentheses, as
in char(*) - this means a pointer to characters. If it says long or int,
that is not a pointer. If you look at the member QLGCNVCS in QSYSINC/H you
will see
void QLGCNVCS(char *,
char *,
char *,
long,
char *);
Note that there is no * after the word "long", so it is not a pointer.
Scott Klement helped me with this some time ago.
You could see what is happening in debug with your own program - can't
debug IBM's stuff. Write a little RPGLE module with a single parameter with
the VALUE keyword - you'll need to use a prototype and procedure interface
combination, not a *PLIST. Then call it with a CLLE module, passing the
*DEC variable. When I did this, the integer in the RPG module had the value
x'520019FF' (1375738367).
My CLLE is
pgm
dcl &badint *dec (4 0) 234
callprc testptr &badint
endpgm
My RPGLE is
h nomain
dtestptr pr
d 10i 0 value
ptestptr b export
dtestptr pi
d intbyvalue 10i 0 value
d moveto s 10i 0
/free
moveto = intbyvalue;
/end-free
ptestptr e
Compile each with DBGVIEW(*ALL), then CRTPGM with the CLLE first in order.
STRDBG, set a breakpoint on the assignment statement in the RPGLE, run it
and see what the value is coming in.
HTH
Vern
At 11:42 AM 5/17/2005, you wrote:
>"The &LENGTH parameter in this program is defined as *DEC but the API is
>expecting *INT. The statement
>
>DCL VAR(&LENGTH) TYPE(*DEC) LEN(4) VALUE(50)
>
>is creating &LENGTH with a value of x'0000050F' which the API is
>interpreting as 1295 - just a bit longer than the 50 bytes you are really
>passing. On V5R3 you could change to
>
>DCL VAR(&LENGTH) TYPE(*INT) VALUE(50)
>
>which would give you x'00000032' (a length of 50). Alternatively you
>could
>
>DCL VAR(&LENGTH) TYPE (*CHAR) LEN(4) VALUE(x'00000032')
>
>Your API call may have appeared to be working OK on prior releases, but
>you
>were inadvertently corrupting storage which may have caused other
>application functions to work "strangely"."
>
>Thank you Bruce for pin-pointing the error and for your advise on this
>issue. This is oficially the first API I work with and they are tricky
>when you do not know them too much :o)
>
>Thanks again!
>
>
>Peter Vidal
>PALL Corporation / SR Programmer Analyst, IT Development Group
>10540 Ridge Rd., Ste 203, New Port Richey, FL 34654-5111
>http://www.pall.com
>
>"Courage is the strength or choice to begin a change. Determination is the
>persistence to continue in that change."
>-- Anonymous --
>--
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