[sqlite] Is this code OK?
Hi, ALL,
Here is the code I'm trying to use:
char *errmsg = NULL;
sqlite3_exec( handle, BEGIN, 0, 0, errmsg );
if( sqlite3_exec( , errmsg ) != SQLITE_OK )
{
printf( Error executing query: %s, sqlite3_errmsg( m_handle ) );
sqlite3_exec( handle, ROLLBACK, 0, 0, errmsg );
}
Can I reuse errmsg variable like this or do I have to call sqlite3_free()
and then execute ROLLBACK statement?
Thank you.
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Re: [sqlite] Is this code OK?
On Thu, Sep 19, 2013 at 8:55 AM, Igor Korot ikoro...@gmail.com wrote: Can I reuse errmsg variable like this or do I have to call sqlite3_free() and then execute ROLLBACK statement? Per the API docs: ** ^If an error occurs while evaluating the SQL statements passed into ** sqlite3_exec(), then execution of the current statement stops and ** subsequent statements are skipped. ^If the 5th parameter to sqlite3_exec() ** is not NULL then any error message is written into memory obtained ** from [sqlite3_malloc()] and passed back through the 5th parameter. ** To avoid memory leaks, the application should invoke [sqlite3_free()] ** on error message strings returned through the 5th parameter of ** of sqlite3_exec() after the error message string is no longer needed. ** ^If the 5th parameter to sqlite3_exec() is not NULL and no errors ** occur, then sqlite3_exec() sets the pointer in its 5th parameter to ** NULL before returning. -- - stephan beal http://wanderinghorse.net/home/stephan/ http://gplus.to/sgbeal ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
Stephan, On Thu, Sep 19, 2013 at 12:46 AM, Stephan Beal sgb...@googlemail.comwrote: On Thu, Sep 19, 2013 at 8:55 AM, Igor Korot ikoro...@gmail.com wrote: Can I reuse errmsg variable like this or do I have to call sqlite3_free() and then execute ROLLBACK statement? Per the API docs: ** ^If an error occurs while evaluating the SQL statements passed into ** sqlite3_exec(), then execution of the current statement stops and ** subsequent statements are skipped. ^If the 5th parameter to sqlite3_exec() ** is not NULL then any error message is written into memory obtained ** from [sqlite3_malloc()] and passed back through the 5th parameter. ** To avoid memory leaks, the application should invoke [sqlite3_free()] ** on error message strings returned through the 5th parameter of ** of sqlite3_exec() after the error message string is no longer needed. ** ^If the 5th parameter to sqlite3_exec() is not NULL and no errors ** occur, then sqlite3_exec() sets the pointer in its 5th parameter to ** NULL before returning. OK, so I guess I have to call sqlite3_free(). Now, I do have to execute ROLLBACK statement, right? Thank you. -- - stephan beal http://wanderinghorse.net/home/stephan/ http://gplus.to/sgbeal ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
On Thu, Sep 19, 2013 at 10:06 AM, Igor Korot ikoro...@gmail.com wrote: OK, so I guess I have to call sqlite3_free(). Now, I do have to execute ROLLBACK statement, right? Correct - IMO, you have all the pieces in the right place, you just need to free the errmsg string. (i assume you have a corresponding COMMIT somewhere down further).) But... you're not using the error message: printf( Error executing query: %s, sqlite3_errmsg( m_handle ) ); sqlite3_exec( handle, ROLLBACK, 0, 0, errmsg ); instead you're using sqlite3_errmsg(), which means you don't need errmsg unless you use it at another place which isn't shown here. What's the difference between errmsg and calling sqlite3_errmsg()? i'm not sure there is one, and one of the astute listers will probably see this and explain the difference (if any) to us. -- - stephan beal http://wanderinghorse.net/home/stephan/ http://gplus.to/sgbeal ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
Stephan, On Thu, Sep 19, 2013 at 1:09 AM, Stephan Beal sgb...@googlemail.com wrote: On Thu, Sep 19, 2013 at 10:06 AM, Igor Korot ikoro...@gmail.com wrote: OK, so I guess I have to call sqlite3_free(). Now, I do have to execute ROLLBACK statement, right? Correct - IMO, you have all the pieces in the right place, you just need to free the errmsg string. (i assume you have a corresponding COMMIT somewhere down further).) Yes, I do. ;-) But... you're not using the error message: printf( Error executing query: %s, sqlite3_errmsg( m_handle ) ); sqlite3_exec( handle, ROLLBACK, 0, 0, errmsg ); instead you're using sqlite3_errmsg(), which means you don't need errmsg unless you use it at another place which isn't shown here. What's the difference between errmsg and calling sqlite3_errmsg()? i'm not sure there is one, and one of the astute listers will probably see this and explain the difference (if any) to us. It would be interesting to know the difference (if any). At least I (and probably someone else) will know what is better to use. Thank you. -- - stephan beal http://wanderinghorse.net/home/stephan/ http://gplus.to/sgbeal ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
On 19 Sep 2013, at 9:09am, Stephan Beal sgb...@googlemail.com wrote: What's the difference between errmsg and calling sqlite3_errmsg()? No difference in terms of the result, they're just to cope with two different programming styles. The function is provided for situations where you have already lost touch with errmsg or never kept it to start with. By the way, Igor, if this code is being shipped away from your own personal computer you should theoretically be checking the result returned by the execution of BEGIN too. Depending on what goes wrong, it may be the BEGIN which fails, and the result code from subsequent operations wouldn't tell you what the real problem is. Though you may have just simplified your code for posting. Simon. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
On 9/19/2013 2:55 AM, Igor Korot wrote: Here is the code I'm trying to use: char *errmsg = NULL; sqlite3_exec( handle, BEGIN, 0, 0, errmsg ); if( sqlite3_exec( , errmsg ) != SQLITE_OK ) As you are not checking the return value of the first sqlite3_exec, and are not using the error message it returns - why do you pass errmsg at all? Just pass NULL there. If you do pass a non-NULL pointer as the last parameter, then SQLite would allocate memory for it. You should then free said memory, or else you leak it. -- Igor Tandetnik ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
Hi, Simon, On Thu, Sep 19, 2013 at 5:16 AM, Simon Slavin slav...@bigfraud.org wrote: On 19 Sep 2013, at 9:09am, Stephan Beal sgb...@googlemail.com wrote: What's the difference between errmsg and calling sqlite3_errmsg()? No difference in terms of the result, they're just to cope with two different programming styles. The function is provided for situations where you have already lost touch with errmsg or never kept it to start with. By the way, Igor, if this code is being shipped away from your own personal computer you should theoretically be checking the result returned by the execution of BEGIN too. Depending on what goes wrong, it may be the BEGIN which fails, and the result code from subsequent operations wouldn't tell you what the real problem is. Though you may have just simplified your code for posting. Yes, the check code omitted for simplicity. And thank you for clarification. It is hard to imagine the situation when the variable will go out of scope, but that's OK. Simon. ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
Hi, Igor, On Thu, Sep 19, 2013 at 5:54 AM, Igor Tandetnik i...@tandetnik.org wrote: On 9/19/2013 2:55 AM, Igor Korot wrote: Here is the code I'm trying to use: char *errmsg = NULL; sqlite3_exec( handle, BEGIN, 0, 0, errmsg ); if( sqlite3_exec( , errmsg ) != SQLITE_OK ) As you are not checking the return value of the first sqlite3_exec, and are not using the error message it returns - why do you pass errmsg at all? Just pass NULL there. I'm. See my reply to Simon. But as he explain, I changed my code to use sqlite3_errmsg() and am passing 0 to sqlite3_exec(). If you do pass a non-NULL pointer as the last parameter, then SQLite would allocate memory for it. You should then free said memory, or else you leak it. Yes, I understand that. My question was more about re-using the variable between to calls to SQLite. Thank you. -- Igor Tandetnik __**_ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-**bin/mailman/listinfo/sqlite-**usershttp://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] Is this code OK?
On 9/19/2013 5:43 PM, Igor Korot wrote: If you do pass a non-NULL pointer as the last parameter, then SQLite would allocate memory for it. You should then free said memory, or else you leak it. Yes, I understand that. My question was more about re-using the variable between to calls to SQLite. Well, you can reuse the variable *after* you free the memory it points to. Consider: // OK char* p = new char[42]; delete[] p; p = new char[84]; // Not OK char* p = new char[42]; p = new char[84]; Your situation is the same: sqlite3_exec effectively acts as a memory allocation routine. It's not reusing the variable per se that's a problem, it's losing a pointer to memory that was allocated but not yet freed. -- Igor Tandetnik ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
