Hi, Michael:
I made a mistake on the example. It should be 'ucLen' instead of 'unLen'.
There is no specific reason to use the pointer of local variable
(stack-based) to call another function. I just do not want to allocate
memory and free it again.
Multi-process means there are several processes running on the system. No
pre-empt process means other process can not pre-empt the process which
calls FunctionB.
I guess there is a mistake in the system. But I can't find any clue. There
are many libs for me to include and reference. I need some clue to find a
way to explain and investigate this problem.
Br/Laurent
From: Michael Torrie <[EMAIL PROTECTED]>
Reply-To: Provo Linux Users Group Mailing List <[email protected]>
To: Provo Linux Users Group Mailing List <[email protected]>
Subject: Re: Who modified my local variable?
Date: Mon, 12 Jun 2006 06:42:55 -0600
On Mon, 2006-06-12 at 15:58 +0800, Laurent R wrote:
> Hi,
> I met a problem as show below:
>
> void FunctionA(unsigned char *pLen)
> {
> *pLen = 16;
> printf("T2 %d\r\n", *pLen);
> return;
> }
>
> void FunctionB(void)
> {
> unsigned char ucLen = 0;
> printf("T1 %d\r\n", unLen);
> FunctionA(&ucLen);
> printf("T3 %d\r\n", unLen);
> return;
> }
>
> It is a multi-process project. One of the process will call FunctionB,
but
> the result is not 0->16->16. It is 0->16->0. There are several other
> processes running in the backgroud. But there is no pre-empt process
related
> to this function, or re-entry call of this function. I don't know who
modify
> my local variable?
> Who can help me to think out other reason to modify my local variable
in
> this example?
What does the debugger say?
When you say there are multiple processes, does that mean that these
functions are called simultaneously by different processes? I don't
know what you mean by "no pre-empt process."
Step through your program with a debugger and watch the variable. when
it changes examine the code. My gut feeling is you have memory
corruption going on in another part of your program or these functions
that's clobbering this variable somehow. Is there a reason you need to
pass a pointer to a local (stack-based) variable to another function?
Trying to compile this fragment says that unLen is undeclared. Did you
mean to say "ucLen?" When I change it to ucLen, the fragment works just
as you would expect (0,16,16), so the problem is definitely in your
surrounding code.
> Br/Laurent
>
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