return queryvalue0toString;

The code snippet you provided is incomplete and lacks context. However, assuming that query is an object of a class that has a method value() which returns a value at index 0, and that value is of type QString, then query.value(0).toString() will return the value at index 0 as a QString object converted to a string.

Here's an example of how this code snippet might be used:

QSqlQuery query;
// ... execute a query and fetch the result

QString result = query.value(0).toString();

In this example, result will store the value at index 0 of the query result as a string.