[sqlite] sqlite3_free_table question

[Richard Boyd]

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

[Richard Boyd]

Dennis,

Ok thanks for the quick response. I'll persevere with that then and get back
if I still have problems.

Thanks,
Richard. 

[sqlite] sqlite3_free_table question

[Richard Boyd]

Hi all,

Firstly, forgive me for a slightly naïve question; I don’t normally code in
C and I’m 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).

I’ve tried quite a few permutations and am never quite sure if I’ve 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.

[sqlite] sqlite3 dll for C#

[Richard Boyd]

Hi,
 
I managed to find a dll for sqlite2 that will work with C#. Has anyone any
idea where I can find a dll for sqlite3?
 
Thanks,
R.

RE: [sqlite] quotes around text in returned data?

[Richard Boyd]

Thanks all!

I'll give those a go.

-Richard.

RE: [sqlite] quotes around text in returned data?

[Richard Boyd]

>>Use the built-in quote() function.
--

Ok I think I found it. (http://www.sqlite.org/lang_expr.html)
I'm not really familiar with this method of calling a function in an
expression. Is there away to have it only quote the TEXT columns and not the
INTEGER columns, or does it do this anyway by default?

Ideally I'd like the entire row returned with TEXT strings in quotes but
everything else left as normal.

SELECT * from Table0 quote(??some expression in here??);


Sorry, I'm a bit lost.  Are there any code snippets on the usage?

Thanks again.
R.

RE: [sqlite] quotes around text in returned data?

[Richard Boyd]

>>Use the built-in quote() function.
--

Just what I'm after (huge sigh of relief) Is it sqlite3_quote?

I had a search through the documentation and didn't come up with anything.
Obviously I didn't look hard enough. I'll go back and look again.

Thanks very much for the quick response and apologies if this is a common
question.
R.

[sqlite] quotes around text in returned data?

[Richard Boyd]

Hi,

Is there anyway to get Sqlite to add 'quotes' around text strings when it is
returning data from a select command?

For example:

I have a table called table0 which is created using
CREATE TABLE table0 (col1 INTEGER, col2 TEXT, col3 INTEGER);

I have a row in the table
1|this is a text string|2

Now to insert that I need something like:
INSERT INTO table0 values(1,'this is a text string',2);

When I go to retrieve this data using
SELECT * from table0;
I get:
1|this is a text string|2
Which I suppose is correct. But what happens if I want to put this row into
another table???  I need to parse it and add in the quotes (' ') around the
text string??

The problem I have is that I retrieve data from a remote database then pass
over a network to be received and placed into a local table. OF course I get
an error because Sqlite complains about the string.

Can anyone help with this problem???

Thanks in advance.
R.

RE: [sqlite] Function to find the size returned data size from a SELECT??

[Richard Boyd]

OK Thanks for your reply. Yeah, I know that sqlite3_get_table() allocates
the memory for me, but thanks for the heads up any way!

I think the possibility of checking the number of rows will be sufficient
for my purposes...

If I don't check is there not a possibility of there not being enough memory
to fit the returned data? I guess Sqlite checks for this when doing the
malloc? Is there a specific error returned when this is the case (i.e. it
runs out of memory)? It's hardly likely to happen but I need to handle the
case none the less...

Thanks again,
Richard.


> I was wondering if there was a way to find the size of data that will be
> returned before actually making the call to sqlite3_get_table which will
> return a pointer to a malloc'd memory location. My question is really: can
I
> find the required memory size before the call?

The short answer is no, not without executing a "SELECT count() ..."
statement to figure out how many rows will be returned by your statement.

Sanity check: You know that sqlite3_get_table() allocates the memory 
for you, right (which you then free later using sqlite3_free_table())? You 
don't have to supply your own malloc'd blob.

[sqlite] Function to find the size returned data size from a SELECT??

[Richard Boyd]

Hi,
 
I was wondering if there was a way to find the size of data that will be
returned before actually making the call to sqlite3_get_table which will
return a pointer to a malloc'd memory location. My question is really: can I
find the required memory size before the call?
 
Thanks in advance,
Richard.
 

RE: [sqlite] correct use of sqlite3_get_table

[Richard Boyd]

Ok thanks for responding...

That was my understanding but I was wondering why it only returned 1 Row in
*pnRow. I've figured it out now (I think). The first row contains the column
name but does not count as a result. Hence the 1 row that is referred to in
*pnRow returned from sqlite3_get_table() is the single result I'm after.

Lo and behold, when I check the 2nd string referenced by the result pointer,
I get what I'm after!

Many thanks!
Richard.

-Original Message-
From: Dennis Cote [mailto:[EMAIL PROTECTED] 
Sent: 03 March 2005 19:31
To: sqlite-users@sqlite.org
Subject: Re: [sqlite] correct use of sqlite3_get_table

Richard Boyd wrote:

> Hi all,
>
> I’m trying to use sqlite3_get_table() to execute SQL commands on a 
> database. I’ve included a code snippet below.
>
> The problem I’m having is that when I execute the "SELECT 
> MAX(time_stamp) FROM table32;” command using sqlite3_get_table() I 
> only get one column and 1 row returned and the result contains 
> “MAX(time_stamp)” rather than the value I’m after. When I run the same 
> command in sqlite3.exe shell I get the desired result (a single number).
>
> Any one any ideas where I’m going wrong with this??
>
Richard,

You need to read the documentation for the sqlite3_get_table() function 
at http://www.sqlite.org/capi3ref.html#sqlite3_get_table. It explains 
how the column header information is returned along with the actual 
data. You are looking at the heading for your column, the data is 
further into the results array.

HTH
Dennis Cote


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[sqlite] correct use of sqlite3_get_table

[Richard Boyd]

Hi all,

 

I’m trying to use sqlite3_get_table() to execute SQL commands on a database. I’ve
included a code snippet below. 

 

The problem I’m having is that when I execute
the "SELECT MAX(time_stamp)
FROM table32;” command using sqlite3_get_table() I only get one column
and 1 row returned and the result contains “MAX(time_stamp)”
rather than the value I’m after. When I run the same command in
sqlite3.exe shell I get the desired result (a single number). 

 

Any one any ideas where I’m going wrong with
this??

 

TIA

-Richard.

 



 

rc
= sqlite3_open("testdb", &db);

  if( rc )

  {

    fprintf(stderr, "Can't open database: %s\n",
sqlite3_errmsg(db));

   
sqlite3_close(db);

    exit(1);

  }

 

  printf ("about to execute the
rxd command\n");

  printf ("%s\n",
command);

  rc = sqlite3_get_table(db,

 "SELECT MAX(time_stamp) FROM
table32;",//command,

 &tresults->results,  //&zResult,

 &tresults->numrows,  //&numrows,

 &tresults->numcols,  //&numcols,

 &tresults->err_msg); //&zErrMsg);

 



 






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