mco_cursor_check

RT

Check the internal structure of the cursor.

Prototype

 
    MCO_RET	mco_cursor_check(	/*IN*/ mco_trans_h t, /*IN*/ mco_cursor_h c);
 

Arguments

Description

This function checks the internal structure of the cursor. It returns MCO_S_OK if the cursor’s internal structure is valid and the index that the cursor is built for has not been changed. Cursors are valid across transactions, so applications may need to know if the current cursor is valid when it is reused in a transaction different from the one that created it.

Note that it is normal for an application to call mco_w_obj_from_cursor() many times, so the effect of this check can have a significant impact on performance. For this reason the part of this function that checks the validity of the object handle is present only in the debug version of the runtime libraries – it is removed from the release version of the libraries. As a result, where in some cases mco_w_obj_from_cursor() might return MCO_E_CURSOR_INVALID when using the debug libraries, the same function call when using the release version of the libraries can return MCO_S_OK. So developers should take care to handle all return codes from cursor functions and eliminate any MCO_E_CURSOR_INVALID situations during development with the debug libraries.

Return Codes

Example

 
    Application snippet:

     
    const char * dbname = "SimpleDb";
     
    int main(int argc, char* argv[])
    {
        mco_db_h db;
        MCO_RET rc;
        mco_device_t       dev;
        mco_db_params_t    db_params;
        mco_trans_h t;
        mco_cursor_t c;
        MCO_CURSOR_TYPE ctype;
         
        ...
        rc = mco_db_open_dev( dbname, simple_get_dictionary(), &dev, 1, &db_params );
        if ( MCO_S_OK != rc )
        {
            rc = mco_db_connect(  dbname, &db );
            ...
            rc = mco_trans_start(db, MCO_READ_ONLY, MCO_TRANS_FOREGROUND, &t);
            if ( MCO_S_OK == rc )
            {
                ...
                A_list_cursor( t, &c);
                ...
                rc = mco_cursor_check( t, &c );

                ...
        }
        ...
    }
     
 

Files