[sqlite] How to use sqlite3_blob_open when the blob column is empty?

[zhangkai.gis]

Thanks,I have set a value for the blob.Then sqlite3_blob_open returns 
SQLITE_OK.Then I use sqlite3_blob_write to update the blob.I notice that.It 
must have enough capacity to hold the writes.

2016-03-04 

zhangkai.gis