Re: [sqlite] GCC give a warning while passing a struct as the, user data to the callback function of sqlite3_exec()

[Midmay]

Enrique Ramirez wrote:
> I noticed what you mean (to reply to my own post). I just noticed the
> original subject and this thread's subject are different:
> 
> (original) [sqlite] GCC give a warning while passing a struct as the
> user data to the callback function of sqlite3_exec()
> (this thread) [sqlite] GCC give a warning while passing a struct as
> the, user data to the callback function of sqlite3_exec()
> 
> Notice the comma? Maybe you modified it by mistake. Gmail uses
> subjects to thread messages.

Oh, I didn't notice that I have add an ',' in the second mail.

Thank you for replying.
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Re: [sqlite] GCC give a warning while passing a struct as the, user data to the callback function of sqlite3_exec()

[Midmay]

Enrique Ramirez wrote:
> Looking at your address I can see you also use gmail. Threading for
> this message is working fine for me. Are you using the web client or
> an external mail program?
> 


In fact, I'm using thunderbird, but it may doesn't matters. When i
subscribed, I turn digest mode on, may be it cause the issues. Now I
have turn it off, seems that my reply before has been list correctly.

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Re: [sqlite] GCC give a warning while passing a struct as the, user data to the callback function of sqlite3_exec()

[Midmay]

Greetings,

> As Michael Knigge has suggested, you may just rename the parameter to
> something else and then have something like
>
>MyStruct* data = (MyStruct*)foo;
>
> as the first line in your callback() function.

Got it.

Sorry but I make a mistake before, the '3rd argument' ought to be '4th
argument', so the question should be:

It means that while passing the 4th argument in sqlite3_exec(), the
argument has been casted to void* ?

However, thank you for your explanation for the callback function.


I have another problem now, it sounds silly but...

Each time I reply, it create a new topic, but not listing the reply
under the original mail. How to make my reply mail is exactly list under
the original mail somebody posted?



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Re: [sqlite] GCC give a warning while passing a struct as the, user data to the callback function of sqlite3_exec()

[Midmay]

Thank you, Markus!

> Simply change the type of the first argument to your callback function
> to void* and the problem should go away. Of course you'll then have to
> cast back to MyStruct* inside callback() to actually use the value.

It works. Just ((MyStruct *) data)->x looks strange.

> The problem here is the type of your callback() function. By declaring
> the first argument to it as MyStruct*, rather than void* as in the
> function pointer type of the 3rd argument to sqlite3_exec(), you're
> creating an incompatible function pointer type.

It means that while passing the 3rd argument in sqlite3_exec(), the
argument has been casted to void* ?

BTW: It is the first time I use mail list, hope I'm replying correctly.
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[sqlite] GCC give a warning while passing a struct as the user data to the callback function of sqlite3_exec()

[Midmay]

I declare a struct and pass it as the 4th argument of sqlite3_exec(),
and define the 1st argument of callback function a pointer to this kind
of struct. while compiling, GCC give a warning like this:
ae.c: In function ‘main’:
ae.c:56: warning: passing argument 3 of ‘sqlite3_exec’ from
incompatible pointer type


however, the program runs well. What may causing the warning? what
should i do to get rid of this warning.

Thanks!

Here is an simple example:

#include 
#include 
#include 

typedef struct
{
int x;
int y;
}MyStruct;


static int callback(MyStruct *data, int argc, char **argv, char
**azColName){
   int i;
   printf ("%d, %d\n", data->x, data->y);

   for(i=0; ix = 1;
   data->y = 2;


   if( argc!=3 ){
 fprintf(stderr, "Usage: %s DATABASE SQL-STATEMENT\n", argv[0]);
 exit(1);
   }
   rc = sqlite3_open(argv[1], );
   if( rc != SQLITE_OK){
 fprintf(stderr, "Can't open database: %s\n", sqlite3_errmsg(db));
 sqlite3_close(db);
 exit(1);
   }
   rc = sqlite3_exec(db, argv[2], callback, data, );
   if( rc!=SQLITE_OK ){
 fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
   }
   sqlite3_close(db);

   free (data);
   return 0;
}
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