1) in foo::func, turn the global access into a parameter

void foo::func(const QMap<...>& features)
{
// no more using the global
    for (auto x : features) /* stuff */
}

2) if necessary, turn the parameter into a member

class foo
{
QMap<QByteArray, Feature> *features
public:
    void some_setter(const QMap<QByteArray, Feature> &features);
};

void foo::func()
{
    for (auto x : features) /* now fine */
}