On 25/07/2008, at 12:32 AM, Lim Hock-Chai wrote:

Uuumm, may be the CL is the problem. I call the C program straight from
command line and it works fine (no junk in stdout).

Which is exactly what I told you. As Scott pointed out in a more verbose fashion: character literals are automatically null-terminated by the CALL command (even if run from within a CL program--which I admit I did not know but then I think I've never passed character literals into a C program from a CL program) but when you pass variables on the CALL **YOU** are responsible for ensuring appropriate null-termination.

I guess the debugger lie to me.

No, it doesn't.

When I call the C program thru the CL program and do below in debugger
eval *argv[1] :s

it shows me
*argv[1] :s = "NOCC07QA "

I though :s tells debugger that the pointer is a null terminator string.
How can debugger show correct data if there is no terminator on position
30 of argv[1]?

The debugger defaults to showing only the first 30 bytes of string data unless a null-terminator is encountered before that limit. It does this for the very reason you have discovered: that if a developer fails to correctly null-terminate a string the debugger will not try to dump all of main storage (or maybe *only* 16MB). The help text in the debugger under C/C++ string examples explains this. It's probably in other documentation too but I can't be bothered looking for it.

Next time you debug and have failed to properly null-terminate run:
EVAL *argc[1]:s 300
and see what happens.

Why did you see blanks after NOCC07QA instead of junk? Recall what the CALL command does with character values and the magic limit of 32.

Doesn't really matter WHY. The problem is you failed to null- terminate the input strings for C.

Anyway, I change the CL to be as below and it appears to correct the

That is the correct approach and it is shown in the examples in the C/ C++ Programmer's Guide in the sections discussing inter-program calls.

Simon Coulter.
FlyByNight Software OS/400, i5/OS Technical Specialists

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