Re: [sqlite] sqlite3_free_table question
On 6/29/06, Richard Boyd <[EMAIL PROTECTED]> wrote: I now check for NULL to be sure that I'm trying to free up a pointer that actually points to something. Is there an easy way for me to ensure that the memory has been successfully freed up? I understand this might be a basic C question rather than a specific Sqlite question, so apologies for that... If you're using malloc()/free() there is no indication returned when you call free(). It's assumed to always work. What people typically do is set the pointer to NULL if it's not pointing to a valid allocated block of memory.
[sqlite] sqlite3_free_table question
Hi again,
I now check for NULL to be sure that I'm trying to free up a pointer that
actually points to something. Is there an easy way for me to ensure that the
memory has been successfully freed up? I understand this might be a basic C
question rather than a specific Sqlite question, so apologies for that...
Thanks again,
Richard.
-Original Message-
From: Dennis Cote [mailto:[EMAIL PROTECTED]
Sent: 28 June 2006 21:46
To: sqlite-users@sqlite.org
Subject: Re: [sqlite] sqlite3_free_table question
Richard Boyd wrote:
> Basically I have a structure I use to hold data results:
>
> //=
> typedef struct {
> char *sqlStatement; // Either the sqlstatement to be executed or the
> last statement that was executed
> char **results; // the result stored in an array
> char *err_msg; // the error message
> intnumrows; // number of rows of results
> intnumcols; // the number of columns of data returned
> } RESULT_T;
> //===
>
> I pass this structure to a wrapper function that ultimately calls
> sqlite3_get_table and returns the results structure on tresults
>
> //===
> int execute_command (size_t nbytes, char *command, RESULT_T
> *tresults)
> //===
>
> In the function that calls execute_command(), I want to free up the memory
> that was allocated by sqlite3_get_table().
>
> Do I just call the free function like this:
> sqlite3_free_table(tresults.results); (assuming that I created a variable
> called 'tresults' of type RESULT_T in the calling function).
>
> Also, how do I free up the error messages? What if there are no results
> returned by sqlite3_get_table, can I still attempt to free up the memory
> with 'sqlite3_free_table'
>
> I appreciate you reading down this far, and sorry if my code snips are
hard
> to follow!!
>
>
Richard,
Your call to sqlite3_free_table is correct.
You free the error message by calling sqlite3_free(tresult.err_msg).
If either pointer returned by sqlite3_get_table() is NULL, then no
memory was allocated, so there is no need to free it, however I believe
it should be safe to call the free routines with a NULL pointer.
HTH
Dennis Cote
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Re: [sqlite] sqlite3_free_table question
Dennis Cote <[EMAIL PROTECTED]> wrote: > Christian Smith wrote: > > sqlite3_free, and the sqlite3GenericFree that implements it asserts > > that the pointer passed in is not NULL. So it is not safe to pass in a > > NULL pointer. > > > > It should be safe, if sqlite3_free and co are mimicking the behaviour > > of the libc free. The current CVS implementation should therefore > > check for NULL and do nothing in this case. > > > I agree, this should be fixed. You should file a bug report. > 2 days ago. See http://www.sqlite.org/cvstrac/chngview?cn=3298 -- D. Richard Hipp <[EMAIL PROTECTED]>
Re: [sqlite] sqlite3_free_table question
Christian Smith wrote: sqlite3_free, and the sqlite3GenericFree that implements it asserts that the pointer passed in is not NULL. So it is not safe to pass in a NULL pointer. It should be safe, if sqlite3_free and co are mimicking the behaviour of the libc free. The current CVS implementation should therefore check for NULL and do nothing in this case. I agree, this should be fixed. You should file a bug report. Dennis Cote
Re: [sqlite] sqlite3_free_table question
Dennis Cote uttered: Your call to sqlite3_free_table is correct. You free the error message by calling sqlite3_free(tresult.err_msg). If either pointer returned by sqlite3_get_table() is NULL, then no memory was allocated, so there is no need to free it, however I believe it should be safe to call the free routines with a NULL pointer. From the discussion the other day, I looked at the implementation of sqlite3_free, and the sqlite3GenericFree that implements it asserts that the pointer passed in is not NULL. So it is not safe to pass in a NULL pointer. It should be safe, if sqlite3_free and co are mimicking the behaviour of the libc free. The current CVS implementation should therefore check for NULL and do nothing in this case. HTH Dennis Cote Christian -- /"\ \ /ASCII RIBBON CAMPAIGN - AGAINST HTML MAIL X - AGAINST MS ATTACHMENTS / \
RE: [sqlite] sqlite3_free_table question
Dennis, Ok thanks for the quick response. I'll persevere with that then and get back if I still have problems. Thanks, Richard.
Re: [sqlite] sqlite3_free_table question
Richard Boyd wrote:
Basically I have a structure I use to hold data results:
//=
typedef struct {
char *sqlStatement; // Either the sqlstatement to be executed or the
last statement that was executed
char **results; // the result stored in an array
char *err_msg; // the error message
intnumrows; // number of rows of results
intnumcols; // the number of columns of data returned
} RESULT_T;
//===
I pass this structure to a wrapper function that ultimately calls
sqlite3_get_table and returns the results structure on tresults
//===
int execute_command (size_t nbytes, char *command, RESULT_T
*tresults)
//===
In the function that calls execute_command(), I want to free up the memory
that was allocated by sqlite3_get_table().
Do I just call the free function like this:
sqlite3_free_table(tresults.results); (assuming that I created a variable
called ‘tresults’ of type RESULT_T in the calling function).
Also, how do I free up the error messages? What if there are no results
returned by sqlite3_get_table, can I still attempt to free up the memory
with ‘sqlite3_free_table’
I appreciate you reading down this far, and sorry if my code snips are hard
to follow!!
Richard,
Your call to sqlite3_free_table is correct.
You free the error message by calling sqlite3_free(tresult.err_msg).
If either pointer returned by sqlite3_get_table() is NULL, then no
memory was allocated, so there is no need to free it, however I believe
it should be safe to call the free routines with a NULL pointer.
HTH
Dennis Cote
[sqlite] sqlite3_free_table question
Hi all,
Firstly, forgive me for a slightly naïve question; I dont normally code in
C and Im having problems freeing up memory.
Basically I have a structure I use to hold data results:
//=
typedef struct {
char *sqlStatement; // Either the sqlstatement to be executed or the
last statement that was executed
char **results; // the result stored in an array
char *err_msg; // the error message
intnumrows; // number of rows of results
intnumcols; // the number of columns of data returned
} RESULT_T;
//===
I pass this structure to a wrapper function that ultimately calls
sqlite3_get_table and returns the results structure on tresults
//===
int execute_command (size_t nbytes, char *command, RESULT_T
*tresults)
//===
In the function that calls execute_command(), I want to free up the memory
that was allocated by sqlite3_get_table().
Do I just call the free function like this:
sqlite3_free_table(tresults.results); (assuming that I created a variable
called tresults of type RESULT_T in the calling function).
Ive tried quite a few permutations and am never quite sure if Ive actually
freed up the memory. Is there a fool proof way to check?
Also, how do I free up the error messages? What if there are no results
returned by sqlite3_get_table, can I still attempt to free up the memory
with sqlite3_free_table
I appreciate you reading down this far, and sorry if my code snips are hard
to follow!!
TIA
Richard.
