On Tue, Sep 4, 2018 at 2:11 PM Keith Medcalf <kmedc...@dessus.com> wrote:
> > On Tuesday, 4 September, 2018 14:00, Clemens Ladisch <clem...@ladisch.de> > wrote: > > >Keith Medcalf wrote: > >> 6) If the column type is SQLITE_BLOB > >> a) Retrieve the column value pointer using column_blob > >> b) If the returned pointer is NULL, then an error has occurred > > >"The return value from sqlite3_column_blob() for a zero-length BLOB > >is a NULL pointer." > > Hmmm. Yes. > > " The values returned by sqlite3_column_bytes() and > sqlite3_column_bytes16() do not include the zero terminators at the end of > the string. For clarity: the values returned by sqlite3_column_bytes() and > sqlite3_column_bytes16() are the number of bytes in the string, not the > number of characters. > (for text) column_bytes() returns the number of bytes specified for the string, and has nothing to do with NUL unless you end up with a tranlsation from utf8 to utf16 or vice versa. So it can/will return the number of bytes including nulls in the text. > > Strings returned by sqlite3_column_text() and sqlite3_column_text16(), > even empty strings, are always zero-terminated. The return value from > sqlite3_column_blob() for a zero-length BLOB is a NULL pointer. " > if there is no transform between utf16 or utf8, text returns a pointer which may contain nuls; I do forget, but it may be the buffer is always allocated +1 and include an extra nul... (probably does) Such nuls can be isnerted with the escape '||char(0)||' > > So, an empty string returns a valid pointer but the bytes count is zero. > > For an empty blob, the returned pointer is NULL and the bytes count is > zero. So, for column_text the test for a NULL pointer will indicate an > error. > > In the case of a BLOB if a NULL pointer is returned the error code must be > retrieved and then if and only if the bytes counter is greater than 0 is > the error valid. > > Does this mean that if you are retrieving the value of a blob via the > colmn_blob interface you should ask for the column_bytes first and only > expect a NULL pointer if the bytes count is zero? > > --- > The fact that there's a Highway to Hell but only a Stairway to Heaven says > a lot about anticipated traffic volume. > > > > > > > _______________________________________________ > sqlite-users mailing list > sqlite-users@mailinglists.sqlite.org > http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@mailinglists.sqlite.org http://mailinglists.sqlite.org/cgi-bin/mailman/listinfo/sqlite-users
