Re: [sqlite] SQLITE_STATIC and temporary data
On Wed, Aug 01, 2012 at 04:48:48PM +, Rob Richardson scratched on the wall: > Is "acceptable" good enough? I admit I haven't played with this function > (actually, I never heard of it until today), but from what I read in the > documentation, the case described looked dangerous to me. It's somewhat undefined, and I suspect that's intentional. There are a lot of specifics that are undocumented because they change from version to version of SQLite. > SQLITE_STATIC > seemed to me to imply that the contents of the memory used by the sqlite > statement would never change over the life of the statement. It's more the lifetime of the binding. Which reminds me (and I see others on the list already pointed this out), freeing the memory after a call to _reset() would be a Bad Idea since the binding is still in effect. It would have to be _finalize() or _clear_bindings(). But yes... the key is that the memory remains valid for the lifetime of the binding, not the fact that is or isn't statically allocated. -j > -Original Message- > From: sqlite-users-boun...@sqlite.org > [mailto:sqlite-users-boun...@sqlite.org] On Behalf Of Jay A. Kreibich > Sent: Wednesday, August 01, 2012 12:16 PM > To: General Discussion of SQLite Database > Cc: c...@iki.fi > Subject: Re: [sqlite] SQLITE_STATIC and temporary data > > On Wed, Aug 01, 2012 at 08:49:19PM +1000, Yose Widjaja scratched on the wall: > > Dear Friends, > > > > So SQLITE_STATIC is meant to be used for data that is static. However, > > would it still be safe when it is used with data that expires after > > the > > sqlite3_step() function? > > > > For example: > > > > string hello = "hello world"; > > > > sqlite3_bind(statement, 1, hello.c_str(), hello.size(), > > SQLITE_STATIC); > > > > sqlite3_step(statement); > > > > hello = "moo"; > > > > Would there be anything that can potentially go wrong? I mean, since > > SQLITE_STATIC is meant to imply static stuff, would sqlite cache the > > value in such a way that subsequence SELECT_ statements actually use > > this static value that was passed in through the bind function? > > It would be better to keep the value valid until _reset() or > _finalize() is called, but, yes... this use of SQLITE_STATIC is > acceptable (and somewhat common). > >-j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Intelligence is like underwear: it is important that you have it, but showing it to the wrong people has the tendency to make them feel uncomfortable." -- Angela Johnson ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] SQLITE_STATIC and temporary data
Jay A. Kreibich wrote: > On Wed, Aug 01, 2012 at 08:49:19PM +1000, Yose Widjaja scratched on the wall: >> Dear Friends, >> >> So SQLITE_STATIC is meant to be used for data that is static. However, >> would it still be safe when it is used with data that expires after the >> sqlite3_step() function? >> >> For example: >> >> string hello = "hello world"; >> >> sqlite3_bind(statement, 1, hello.c_str(), hello.size(), SQLITE_STATIC); >> >> sqlite3_step(statement); >> hello = "moo"; >> >> Would there be anything that can potentially go wrong? I mean, since >> SQLITE_STATIC is meant to imply static stuff, would sqlite cache the value >> in such a way that subsequence SELECT_ statements actually use this static >> value that was passed in through the bind function? > > It would be better to keep the value valid until _reset() or No, _reset is NOT enough, as it *won't* clear bindings. You *must* keep data till either sqlite3_clear_bindings or sqlite3_finalize is (successfully) called. > _finalize() is called, but, yes... this use of SQLITE_STATIC is > acceptable (and somewhat common). Above code is certainly incorrect. Maybe you won't be slapped with SIGSEGV immediately (depending on surrounding code and sqlite3 implementation details), but still this is incorrect and unsafe. You should insert sqlite3_clear_bindings(statement); or sqlite3_bind_null(statement, 1); before hello = "moo"; ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
Re: [sqlite] SQLITE_STATIC and temporary data
Is "acceptable" good enough? I admit I haven't played with this function (actually, I never heard of it until today), but from what I read in the documentation, the case described looked dangerous to me. SQLITE_STATIC seemed to me to imply that the contents of the memory used by the sqlite statement would never change over the life of the statement. But please keep in mind that in this case (as in many other cases), my opinion likely to be worth exactly what you have paid for it. RobR -Original Message- From: sqlite-users-boun...@sqlite.org [mailto:sqlite-users-boun...@sqlite.org] On Behalf Of Jay A. Kreibich Sent: Wednesday, August 01, 2012 12:16 PM To: General Discussion of SQLite Database Cc: c...@iki.fi Subject: Re: [sqlite] SQLITE_STATIC and temporary data On Wed, Aug 01, 2012 at 08:49:19PM +1000, Yose Widjaja scratched on the wall: > Dear Friends, > > So SQLITE_STATIC is meant to be used for data that is static. However, > would it still be safe when it is used with data that expires after > the > sqlite3_step() function? > > For example: > > string hello = "hello world"; > > sqlite3_bind(statement, 1, hello.c_str(), hello.size(), > SQLITE_STATIC); > > sqlite3_step(statement); > > hello = "moo"; > > Would there be anything that can potentially go wrong? I mean, since > SQLITE_STATIC is meant to imply static stuff, would sqlite cache the > value in such a way that subsequence SELECT_ statements actually use > this static value that was passed in through the bind function? It would be better to keep the value valid until _reset() or _finalize() is called, but, yes... this use of SQLITE_STATIC is acceptable (and somewhat common). -j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Intelligence is like underwear: it is important that you have it, but showing it to the wrong people has the tendency to make them feel uncomfortable." -- Angela Johnson ___ 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] SQLITE_STATIC and temporary data
On Wed, Aug 01, 2012 at 08:49:19PM +1000, Yose Widjaja scratched on the wall: > Dear Friends, > > So SQLITE_STATIC is meant to be used for data that is static. However, > would it still be safe when it is used with data that expires after the > sqlite3_step() function? > > For example: > > string hello = "hello world"; > > sqlite3_bind(statement, 1, hello.c_str(), hello.size(), SQLITE_STATIC); > > sqlite3_step(statement); > > hello = "moo"; > > Would there be anything that can potentially go wrong? I mean, since > SQLITE_STATIC is meant to imply static stuff, would sqlite cache the value > in such a way that subsequence SELECT_ statements actually use this static > value that was passed in through the bind function? It would be better to keep the value valid until _reset() or _finalize() is called, but, yes... this use of SQLITE_STATIC is acceptable (and somewhat common). -j -- Jay A. Kreibich < J A Y @ K R E I B I.C H > "Intelligence is like underwear: it is important that you have it, but showing it to the wrong people has the tendency to make them feel uncomfortable." -- Angela Johnson ___ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
