# MariaDB Connector/C Data Structures This page describes the public data structures used by MariaDB Connector/C. ### MYSQL The `MYSQL` structure represents one database connection and is used by most of MariaDB Connector/C's API functions. The MYSQL structure needs to be allocated and initialized by the [mysql\_init()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_init) API function. It will be released by the [mysql\_close()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_close) function. {% hint style="info" %} The `MYSQL` structure should be considered as opaque; copying or changing values of its members might produce unexpected results, errors or program crashes. {% endhint %} ### MYSQL\_RES The `MYSQL_RES` structure represents a result set which contains data and metadata information. It will be returned by the [mysql\_use\_result()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_use_result), [mysql\_store\_result()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_store_result) and [mysql\_stmt\_result\_metadata()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-prepared-statement-functions/mysql_stmt_result_metadata) API functions and needs to be released by [mysql\_free\_result()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_free_result). {% hint style="info" %} The `MYSQL_RES` structure should be considered as opaque; copying or changing values of its members might produce unexpected results, errors or program crashes. {% endhint %} ### MYSQL\_ROW `MYSQL_ROW` represents an array of character pointers, pointing to the columns of the actual data row.\ Data will be received by the [mysql\_fetch\_row()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_fetch_row) function. The size of the array is the number of columns for the current row. {% hint style="info" %} After freeing the result set with [mysql\_free\_result()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_free_result) `MYSQL_ROW` becomes invalid. {% endhint %} ### MYSQL\_STMT The `MYSQL_STMT` structure represents a prepared statement handle and is used by MariaDB Connector/C's prepared statement API functions. The MYSQL\_STMT structure needs to be allocated and initialized by the [mysql\_stmt\_init()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-prepared-statement-functions/mysql_stmt_init) function and needs to be released by the [mysql\_stmt\_close()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-prepared-statement-functions/mysql_stmt_close) function. {% hint style="info" %} The `MYSQL_STMT` structure should be considered as opaque; copying or changing values of its members might produce unexpected results, errors or program crashes. {% endhint %} ### MYSQL\_FIELD The `MYSQL_FIELD` structure describes the metadata of a column. It can be obtained by the [mysql\_fetch\_field()](https://mariadb.com/docs/connectors/mariadb-connector-c/api-functions/mysql_fetch_field) function. It has the following members: | | | | | ----------------------- | ------------------ | ------------------------------------------- | | char \* | name | The name of the column | | unsigned int | name\_length | The length of column name | | char \* | org\_name | The original name of the column | | unsigned int | org\_name\_length | The length of original column name | | char \* | table | The name of the table | | unsigned int | table\_length | The length of table name | | char \* | org\_table | The original name of the table | | unsigned int | org\_table\_length | The length of original table name | | char \* | db | The name of the database (schema) | | unsigned int | db\_length | The length of database name | | char \* | catalog | The catalog name (always 'def') | | unsigned int | catalog\_length | The length of catalog name | | char \* | def | default value | | unsigned int | def\_length | The length of default value | | unsigned int | length | The length (width) of the column definition | | unsigned int | max\_length | The maximum length of the column value | | unsigned int | flags | Flags | | unsigned int | decimals | Number of decimals | | enum enum\_field\_types | type | Field type | ### MYSQL\_BIND The `MYSQL_BIND` structure is used to provide parameters for prepared statements or to receive output column value from prepared statements. | | | | | ----------------------- | --------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | unsigned long \* | length | Pointer for the length of the buffer (not used for parameters). The length is ignored for numeric and fixed size data types, as the buffer\_type value determines the size of the data. | | my\_bool \* | is\_nulll | Pointer which indicates if column is NULL (not used for parameters) | | my\_bool \* | error | Pointer which indicates if an error occured | | void \* | buffer | Data buffer which contains or receives data | | char \* | u.indicator | Array of indicator variables for bulk operation parameter | | unsigned long | buffer\_length | Length of buffer | | enum enum\_field\_types | buffer\_type | [Buffer type](https://mariadb.com/docs/connectors/mariadb-connector-c/mariadb-connectorc-types-and-definitions) | | unsigned long | length\_value | Used if length pointer is NULL | | my\_bool | error\_value | Used if error pointer is NULL | | my\_bool | is\_null\_value | Used if is\_null pointer is NULL | | my\_bool | is\_unsigned | Set if integer type is unsigned | | my\_bool | is\_null\_value | Used if value is NULL | ### MYSQL\_TIME The `MYSQL_TIME` structure is used for date and time values in prepared statements. It has the following members: | | | | | --------------------------------- | ------------ | ---------------------------------- | | unsigned int | year | Year | | unsigned int | month | Month | | unsigned int | day | Day | | unsigned int | hour | Hour | | unsigned int | minute | Minute | | unsigned int | second | Second | | unsigned long | second\_part | Fractional seconds (max. 6 digits) | | my\_bool | neg | Negative value | | enum enum\_mysql\_timestamp\_type | time\_type | Type | {% @marketo/form formId="4316" %}