char *query[]

[gert]

Why does query[1] = www ?

int
main(void)
{
char *user="www";
char *password="";
char *database="www";
char *query[]={"SHOW DATABASES;"};
db(user,password,database,query);
}

(gdb) next
12 char *query[]={"SHOW DATABASES;"};
(gdb) next
13 db(user,password,database,query);
(gdb) print query
$5 = {0x400e25 "SHOW DATABASES;"}
(gdb) print query[0]
$6 = 0x400e25 "SHOW DATABASES;"
(gdb) print query[1]
$7 = 0x400e20 "www"
(gdb) print query[2]
$8 = 0x400e24 ""
(gdb) print query[3]
$9 = 0x400e20 "www"
(gdb) print query[4]
$10 = 0x0
(gdb)

source
----------
http://dfo.svn.sourceforge.net/viewv...74&view=markup

[Richard]

gert <ge**********@gmail.comwrites:

Why does query[1] = www ?

Because you are accessing other strings outside of the scope of your
query definition.

Query is an arry of pointers to char with only one element.

query[1] (luckily) out of the bounds of query and happens to be same as
user which is pointing to "www".

(gdb) p query[1]
$4 = 0x804844c "www"
(gdb) p user
$5 = 0x804844c "www"
(gdb)

This is platform specific and you might as well have got a crash.

[gert]

There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?

[gert]

On Jul 15, 6:47 pm, gert <[e-mail]:

There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?

o wait a minute what about

char **query = {"SHOW DATABASES;", 0x0 };

(gdb) print query[4]
$10 = 0x0

How can i force a 0x0 boundary ?

[gert]

On Jul 15, 6:57 pm, gert <[e-mail]:

On Jul 15, 6:47 pm, gert <[e-mail]:

There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?

o wait a minute what about

char **query = {"SHOW DATABASES;", 0x0 };

(gdb) print query[4]
$10 = 0x0

How can i force a 0x0 boundary ?

victory, works like a charm :)

char *query[]={"SHOW DATABASES;",NULL};

[Jens Thoms Toerring]

gert <ge**********@gmail.comwrote:

On Jul 15, 6:47 pm, gert <[e-mail]:

There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?

o wait a minute what about

char **query = {"SHOW DATABASES;", 0x0 };

You should use NULL instead of 0x0 - NULL is null pointer
while 0x0 is an integer constant (and the representation
of a null pointer isn't necessarily all bits 0 as in 0x0).

Now you can use your loop

for (q=0;s=query[q];q++ )

since s will be set to NULL for q==1 amd thus the loop will
end without accessing a non-existing array element.

(gdb) print query[4]
$10 = 0x0

How can i force a 0x0 boundary ?

I don't know what you mean with "0x0 boundary", but you
simply aren't allowed to ty to access elements past the
end of the array and you must find a way to avoid that,
like the one you already came up with, i.e. by having a
NULL pointer as the last element that you can test for.

Regards, Jens
--
\ Jens Thoms Toerring ___ [e-mail]
\__________________________ http://toerring.de

[Army1987]

On Sun, 15 Jul 2007 11:18:03 -0700, Barry Schwarz wrote:

The answer to your question at the start of your post is that you have
performed so much undefined behavior that you are no longer in the
realm of C. Any discussion of query[1] might as well be held in an
astrology newsgroup.

LOL...

--
Army1987 (Replace "NOSPAM" with "email")
"Never attribute to malice that which can be adequately explained
by stupidity." -- R. J. Hanlon (?)

[Richard Heathfield]

Jens Thoms Toerring said:

gert <ge**********@gmail.comwrote:

<snip>

>char **query = {"SHOW DATABASES;", 0x0 };

You should use NULL instead of 0x0 - NULL is null pointer
while 0x0 is an integer constant (and the representation
of a null pointer isn't necessarily all bits 0 as in 0x0).

Whilst I agree that NULL is better, 0x0 will correctly initialise the
pointer to NULL even on platforms where all-bits-zero doesn't mean
NULL. The compiler is required to supply some magic if need be, to
ensure that p = 0 Does The Right Thing.

<snip>

--
Richard Heathfield <http://www.cpax.org.uk>
Email: -www. +rjh@
Google users: <http://www.cpax.org.uk/prg/writings/googly.php>
"Usenet is a strange place" - dmr 29 July 1999

[Flash Gordon]

Jens Thoms Toerring wrote, On 15/07/07 18:20:

gert <ge**********@gmail.comwrote:

<snip>

>char **query = {"SHOW DATABASES;", 0x0 };

You should use NULL instead of 0x0 - NULL is null pointer
while 0x0 is an integer constant (and the representation
of a null pointer isn't necessarily all bits 0 as in 0x0).

<snip>

Using NULL is better style, but an integer constant expression with a
value of 0 as shown by gert is also a valid null pointer constant and
even if null pointers are not all bits zero it will work.
--
Flash Gordon

[Jens Thoms Toerring]

Flash Gordon <sp**@flash-gordon.me.ukwrote:

Jens Thoms Toerring wrote, On 15/07/07 18:20:

gert <ge**********@gmail.comwrote:

<snip>

char **query = {"SHOW DATABASES;", 0x0 };

You should use NULL instead of 0x0 - NULL is null pointer
while 0x0 is an integer constant (and the representation
of a null pointer isn't necessarily all bits 0 as in 0x0).

<snip>

Using NULL is better style, but an integer constant expression with a
value of 0 as shown by gert is also a valid null pointer constant and
even if null pointers are not all bits zero it will work.

Sorry, of course - the 0 is here used where the compiler expects
a pointer, so it will automagically convert it to a NULL pointer.
I guess my brain is starting to boil after a temperature jump of
15 degree C here within 2 days...
Regards, Jens
--
\ Jens Thoms Toerring ___ [e-mail]
\__________________________ http://toerring.de

[Barry Schwarz]

On Sun, 15 Jul 2007 16:57:56 -0000, gert <ge**********@gmail.com>
wrote:

>On Jul 15, 6:47 pm, gert <[e-mail]:

>There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?

o wait a minute what about

char **query = {"SHOW DATABASES;", 0x0 };

Did you try this? Did you not get a compiler diagnostic complaining
about too many initializers?

>

>(gdb) print query[4]
$10 = 0x0

How can i force a 0x0 boundary ?

First tell us what a 0x0 boundary is. Do you mean where the address
is always a multiple of 0x10? If so, there is no way to do so
portably.
Remove del for email

[crox]

On Jul 15, 9:20 pm, [e-mail] (Jens Thoms Toerring) wrote:

gert <[e-mail]:

On Jul 15, 6:47 pm, gert <[e-mail]:

There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?

o wait a minute what about
char **query = {"SHOW DATABASES;", 0x0 };

You should use NULL instead of 0x0 - NULL is null pointer
while 0x0 is an integer constant (and the representation
of a null pointer isn't necessarily all bits 0 as in 0x0).

Now you can use your loop

for (q=0;s=query[q];q++ )

since s will be set to NULL for q==1 amd thus the loop will
end without accessing a non-existing array element.

(gdb) print query[4]
$10 = 0x0

How can i force a 0x0 boundary ?

I don't know what you mean with "0x0 boundary", but you
simply aren't allowed to ty to access elements past the
end of the array and you must find a way to avoid that,
like the one you already came up with, i.e. by having a
NULL pointer as the last element that you can test for.

Regards, Jens
--
\ Jens Thoms Toerring ___ [e-mail]
\__________________________ http://toerring.de

Why not to use?
char *elem;
int i;
....
for(i=0; i < sizeof(query); i++) {
do_something_with(query[i]);
}
It is more straightforward and simple solution, I think.

crox

[Ben Bacarisse]

crox <cr*****@gmail.comwrites:

On Jul 15, 9:20 pm, [e-mail] (Jens Thoms Toerring) wrote:

>gert <[e-mail]:

On Jul 15, 6:47 pm, gert <[e-mail]:
There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?
o wait a minute what about
char **query = {"SHOW DATABASES;", 0x0 };

<snip>

>--
\ Jens Thoms Toerring ___ [e-mail]
\__________________________ http://toerring.de

Don't quote sigs.

Why not to use?
char *elem;
int i;
...
for(i=0; i < sizeof(query); i++) {
do_something_with(query[i]);
}
It is more straightforward and simple solution, I think.

Did you mean 'i < sizeof(query)/sizeof(*query)' perhaps? I am not sure
because of the mysterious 'char *elem;' declaration.

To the OP: if you go this route, take the terminating NULL (0x0) out
of the array and you must, of course, declare 'query' as an array:

char *query[] = { "one", "two" };

--
Ben.

[crox]

On Jul 16, 3:16 pm, Ben Bacarisse <[e-mail]:

crox <[e-mail]:

On Jul 15, 9:20 pm, [e-mail] (Jens Thoms Toerring) wrote:

gert <[e-mail]:
On Jul 15, 6:47 pm, gert <[e-mail]:
There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?
o wait a minute what about
char **query = {"SHOW DATABASES;", 0x0 };

<snip>

--
\ Jens Thoms Toerring ___ [e-mail]
\__________________________ http://toerring.de

Don't quote sigs.

Why not to use?
char *elem;
int i;
...
for(i=0; i < sizeof(query); i++) {
do_something_with(query[i]);
}
It is more straightforward and simple solution, I think.

Did you mean 'i < sizeof(query)/sizeof(*query)' perhaps? I am not sure
because of the mysterious 'char *elem;' declaration.

To the OP: if you go this route, take the terminating NULL (0x0) out
of the array and you must, of course, declare 'query' as an array:

char *query[] = { "one", "two" };

--
Ben.

Oops, sorry I mean:
char *query[] = {"Do 1", "Do 2"};
int i;
...
for(i=0; i < sizeof(query); i++) {
do_something_with(query[i]);
}

[santosh]

crox wrote:

On Jul 16, 3:16 pm, Ben Bacarisse <[e-mail]:

crox <[e-mail]:

On Jul 15, 9:20 pm, [e-mail] (Jens Thoms Toerring) wrote:
>gert <[e-mail]:
On Jul 15, 6:47 pm, gert <[e-mail]:
There goes my carefully thought out NASA for loop :(

for(q=0;s=query[q];q++)

Guess the only solution would be using a max value then ?
o wait a minute what about
char **query = {"SHOW DATABASES;", 0x0 };

<snip>

>--
> \ Jens Thoms Toerring ___ [e-mail]
> \__________________________ http://toerring.de

Don't quote sigs.

Why not to use?
char *elem;
int i;
...
for(i=0; i < sizeof(query); i++) {
do_something_with(query[i]);
}
It is more straightforward and simple solution, I think.

Did you mean 'i < sizeof(query)/sizeof(*query)' perhaps? I am not sure
because of the mysterious 'char *elem;' declaration.

To the OP: if you go this route, take the terminating NULL (0x0) out
of the array and you must, of course, declare 'query' as an array:

char *query[] = { "one", "two" };

--
Ben.

When will you do us the favour of not quoting sigs?

Oops, sorry I mean:
char *query[] = {"Do 1", "Do 2"};
int i;
...
for(i=0; i < sizeof(query); i++) {
do_something_with(query[i]);
}

This is wrong. sizeof(query) will return the size, in bytes of the
array named query. You want the number of elements in the array. For
that, you should do:

sizeof query / sizeof query[0];

This will yield two.