pdo_dbh_t definition
Constants
PDO Driver How-To
PHP Manual

## pdo_stmt_t definition

All fields should be treated as read-only unless explicitly stated otherwise.

# pdo_stmt_t

    /* represents a prepared statement */
    struct _pdo_stmt_t {
        /* driver specifics */
        struct pdo_stmt_methods *methods;

*

    void *driver_data;

**

    /* if true, we've already successfully executed this statement at least
         * once */
        unsigned executed:1;

***

    /* if true, the statement supports placeholders and can implement
         * bindParam() for its prepared statements, if false, PDO should
         * emulate prepare and bind on its behalf */
        unsigned supports_placeholders:2;

****

    /* the number of columns in the result set; not valid until after
         * the statement has been executed at least once.  In some cases, might
         * not be valid until fetch (at the driver level) has been called at least once.
         * */
        int column_count;

*****

    struct pdo_column_data *columns;

******

    /* points at the dbh that this statement was prepared on */
        pdo_dbh_t *dbh;

        /* keep track of bound input parameters.  Some drivers support
         * input/output parameters, but you can't rely on that working */
        HashTable *bound_params;
        /* When rewriting from named to positional, this maps positions to names */
        HashTable *bound_param_map;
        /* keep track of PHP variables bound to named (or positional) columns
         * in the result set */
        HashTable *bound_columns;

        /* not always meaningful */
        long row_count;

        /* used to hold the statement's current query */
        char *query_string;
        int query_stringlen;

        /* the copy of the query with expanded binds ONLY for emulated-prepare drivers */
        char *active_query_string;
        int active_query_stringlen;

        /* the cursor specific error code. */
        pdo_error_type error_code;

        /* used by the query parser for driver specific
         * parameter naming (see pgsql driver for example) */
        const char *named_rewrite_template;
    };

* | The driver must set this during SKEL_handle_preparer.
** | This item is for use by the driver; the intended usage is to store a pointer (during SKEL_handle_factory) to whatever instance data is required to maintain a connection to the database.
*** | This is set by PDO after the statement has been executed for the first time. Your driver can inspect this value to determine if it can skip one-time actions as an optimization.
**** | Discussed in more detail in SKEL_handle_preparer.
***** | Your driver is responsible for setting this field to the number of columns available in a result set. This is usually set during SKEL_stmt_execute but with some database implementations, the column count may not be available until SKEL_stmt_fetch has been called at least once. Drivers that implement SKEL_stmt_next_rowset should update the column count when a new rowset is available.
****** | PDO will allocate this field based on the value that you set for the column count. You are responsible for populating each column during SKEL_stmt_describe. You must set the `precision`, `maxlen`, `name`, `namelen` and `param_type` members for each column. The `name` is expected to be allocated using emalloc; PDO will call efree at the appropriate time.