int sqlite3_blob_write(sqlite3_blob *, const void *z, int n, int iOffset);
This function is used to write data into an open BLOB handle from a caller-supplied buffer. N bytes of data are copied from the buffer Z into the open BLOB, starting at offset iOffset.
This function may only modify the contents of the BLOB; it is not possible to increase the size of a BLOB using this API. If offset iOffset is less than N bytes from the end of the BLOB, SQLITE_ERROR is returned and no data is written. If N is less than zero SQLITE_ERROR is returned and no data is written. The size of the BLOB (and hence the maximum value of N+iOffset) can be determined using the sqlite3_blob_bytes() interface.
An attempt to write to an expired BLOB handle fails with an error code of SQLITE_ABORT. Writes to the BLOB that occurred before the BLOB handle expired are not rolled back by the expiration of the handle, though of course those changes might have been overwritten by the statement that expired the BLOB handle or by other independent statements.
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: sqlite3_blob_read().