Some help with pointers......and passing them around.

[LeTubs]

Hi
I'm think I'm having some problem with pointers.....
namely passing them around...Or I think ? I've used
gdb to find the following (note conn is of type MYSQL *conn).

Program received signal SIGSEGV, Segmentation fault.
0x804a53e in get_next_chunk (conn=Error accessing memory address 0xbf000a38:
Bad address.
) at fmysql.c:315

Is what I'm doing correct below. Also is there any programs or tips to
debug pointers (ie checking values, tracing). Any tips or pointers (no pun
intended) would be greatly appreciated.

Here's what I doing ...

functionA( MYSQL *conn){

struct connect conninfo;

/* Is this correct */
conninfo.conn = conn;

/* then the conninfo is then passed to a thread */
pthread_create(.....,NULL,&somefunction,(void *)&conninfo )
}

struct connect{
MYSQL *conn;
int var1;
int var2;
};

[Jon Willeke]

LeTubs wrote:

I'm think I'm having some problem with pointers.....
namely passing them around...Or I think ? I've used
gdb to find the following (note conn is of type MYSQL *conn).

Program received signal SIGSEGV, Segmentation fault.
0x804a53e in get_next_chunk (conn=Error accessing memory address 0xbf000a38:
Bad address.
) at fmysql.c:315

Is what I'm doing correct below. Also is there any programs or tips to
debug pointers (ie checking values, tracing). Any tips or pointers (no pun
intended) would be greatly appreciated.

Here's what I doing ...

functionA( MYSQL *conn){

struct connect conninfo;

/* Is this correct */
conninfo.conn = conn;

/* then the conninfo is then passed to a thread */
pthread_create(.....,NULL,&somefunction,(void *)&conninfo )
}

struct connect{
MYSQL *conn;
int var1;
int var2;
};

You are passing the address of conninfo, a local variable, to a function
that will cause it to be dereferenced after the end of the containing
function. A similar question is answered in the FAQ:

<http://www.eskimo.com/~scs/C-faq/q7.5.html>

[LeTubs]

"Jon Willeke" <j.***********@verizon.dot.net> wrote in message
news:74******************@nwrdny02.gnilink.net...

LeTubs wrote:

I'm think I'm having some problem with pointers.....
namely passing them around...Or I think ? I've used
gdb to find the following (note conn is of type MYSQL *conn).

Program received signal SIGSEGV, Segmentation fault.
0x804a53e in get_next_chunk (conn=Error accessing memory address 0xbf000a38: Bad address.
) at fmysql.c:315

Is what I'm doing correct below. Also is there any programs or tips to
debug pointers (ie checking values, tracing). Any tips or pointers (no pun intended) would be greatly appreciated.

Here's what I doing ...

functionA( MYSQL *conn){

struct connect conninfo;

/* Is this correct */
conninfo.conn = conn;

/* then the conninfo is then passed to a thread */
pthread_create(.....,NULL,&somefunction,(void *)&conninfo )
}

struct connect{
MYSQL *conn;
int var1;
int var2;
};

You are passing the address of conninfo, a local variable, to a function
that will cause it to be dereferenced after the end of the containing
function. A similar question is answered in the FAQ:

<http://www.eskimo.com/~scs/C-faq/q7.5.html>

Thanks it for making it clear what I'm doing wrong however, due to this I've
actaully spotted
a design error (after looking at the above question, I should make conn a
global variable
( as it won't change after it has been intialised, and don't pass it around,
though not to sure
if this will allowed with threads....anyhow I'll cross that bridge when I
come to it....
But many thanks for pointing what I was doing and the info for C-faq as it
will come in handy
Thanks again

David