Stephan Beal wrote: > On Tue, Nov 1, 2011 at 11:25 PM, Tal Tabakman <tal.tabak...@gmail.com>wrote: > >> second,needless to say that I want to avoid this since it causes mem >> leaks.) >> > > Why would it leak? Are you intentionally NOT calling finalize()? > > >> sqlite3_prepare_v2(handle, query.str().c_str(), >> query.str().length()+1, &m_entrySelectSnumStmt, 0); >> > > Technically speaking, the length you are passing there is not correct. The > +1 accounts for the NUL byte at the end of the string, which prepare() does > not need to see (that said, it seems harmless enough).
No. Take look at prepare_v2 documentation: ** ^If the nByte argument is less than zero, then zSql is read up to the ** first zero terminator. ^If nByte is non-negative, then it is the maximum ** number of bytes read from zSql. ^When nByte is non-negative, the ** zSql string ends at either the first '\000' or '\u0000' character or ** the nByte-th byte, whichever comes first. If the caller knows ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ** that the supplied string is nul-terminated, then there is a small ** performance advantage to be gained by passing an nByte parameter that ** is equal to the number of bytes in the input string <i>including</i> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ** the nul-terminator bytes. ^^^^^^^^^^^^^^^^^^^^^^^^ FWIW, it seems, *only* case when it make sense to bother with nByte argument - when string is *not* nul-terminated; otherwise, it is more efficient to just pass -1, no matter if length is known or not. And std::string::c_str() always nul-terminate string. > Also, because 'query' is-a ostringstream, you are possibly creating 2 unneeded > std::string copies here and you are definitely invoking undefined behaviour > with this part: > > sqlite3_prepare_v2(handle, query.str().c_str(), > > The problem is that query.str() returns a COPY of the string, which you > call c_str() on to get its bytes, and then the copy is destroyed. It is > "likely to work" on many platforms but it is technically undefined. To fix > that: > > std::string const & s( query.str() ); > > (note that a (const &) created this way is guaranteed to stay alive until > the end of the scope) Just get rid of str().length() and don't bother with this :-) > Then use s.c_str() and s.size() instead of query.str().xxx(). _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
