我试图在C ++中将一些Blob数据从一个sqlite表复制到另一个。但是,将数据复制到新表后,它似乎已损坏。所述数据包含一些jpeg图像。我用来从TABLE1复制到TABLE2的代码如下所示:
// Read the blob from the database
int64_t rowID = 0;
sscanf( id.c_str(), "%llu", &rowID );
sqlite3_blob* blobHandle = NULL;
if( sqlite3_blob_open( m_dbHandle_temp, "main", m_currentTileTable.c_str(), "tile_data", rowID, 0, &blobHandle ) != SQLITE_OK )
{
sqlite3_blob_close( blobHandle ); // An SQLite blob will be initialised regardless of the success of 'sqlite3_blob_open'
return false;
}
tiles_insert_statement.append( ")" );
// Copy blob to database
sqlite3_stmt *stmt = 0;
const char* tail;
sqlite3_prepare_v2( m_dbHandle, tiles_insert_statement.c_str(), strlen( tiles_insert_statement.c_str() )+1, &stmt, &tail );
int bindSuccess = sqlite3_bind_blob( stmt, 1, blobHandle, sqlite3_blob_bytes( blobHandle ), SQLITE_TRANSIENT );
if( sqlite3_step( stmt ) != SQLITE_DONE )
printf( "Error message: %s\n", sqlite3_errmsg( m_dbHandle ) );
sqlite3_finalize( stmt );
// close handles
sqlite3_blob_close( blobHandle );
我在上面的代码中做错什么了,我之所以说它已损坏,是因为我正在读取要在图像查看器中显示的android设备上的斑点。可以很好地读取和显示表1中的blob,但是表2中的blob不显示任何内容。任何帮助都将不胜感激。
解决方案:
// Read the blob from the database
int64_t rowID = 0;
sscanf( id.c_str(), "%llu", &rowID );
sqlite3_blob* blobHandle = NULL;
if( sqlite3_blob_open( m_dbHandle_temp, "main", m_currentTileTable.c_str(), "tile_data", rowID, 0, &blobHandle ) != SQLITE_OK )
{
sqlite3_blob_close( blobHandle ); // An SQLite blob will be initialised regardless of the success of 'sqlite3_blob_open'
return false;
}
unsigned int length = sqlite3_blob_bytes( blobHandle );
// TODO - instances of this class OWN the buffer.
// Delete the buffer in the destructor ;)
unsigned char* buffer = new unsigned char[ length ];
if( sqlite3_blob_read( blobHandle, buffer, length, 0 ) != SQLITE_OK )
{
return false;
}
tiles_insert_statement.append( ")" );
sqlite3_stmt *stmt = 0;
const char* tail;
sqlite3_prepare_v2( m_dbHandle, tiles_insert_statement.c_str(), strlen( tiles_insert_statement.c_str() )+1, &stmt, &tail );
int bindSuccess = sqlite3_bind_blob( stmt, 1, buffer, length, SQLITE_TRANSIENT );
if( sqlite3_step( stmt ) != SQLITE_DONE )
printf( "Error message: %s\n", sqlite3_errmsg( m_dbHandle ) );
sqlite3_finalize( stmt );
// close handles
sqlite3_blob_close( blobHandle );
sqlite3_bind_blob
需要一个指向实际Blob数据的指针;不能为此使用Blob句柄。
要将blob数据作为内存块获取,请执行类似的查询,SELECT tile_data FROM MyTable WHERE ...
并使用sqlite3_column_blob读取值。
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