Return The Size Of An Open BLOB

int sqlite3_blob_bytes(sqlite3_blob *);

Returns the size in bytes of the BLOB accessible via the successfully opened BLOB handle in its only argument. The incremental blob I/O routines can only read or overwriting existing blob content; they cannot change the size of a blob.

This routine only works on a BLOB handle which has been created by a prior successful call to sqlite3_blob_open() and which has not been closed by sqlite3_blob_close(). Passing any other pointer in to this routine results in undefined and probably undesirable behavior.

See also lists of Objects, Constants, and Functions.

SQLite is in the Public Domain.
https://sqlite.org/c3ref/blob_bytes.html