QMap operator <()

Question

I'm not sure to understand the docs correctly. I want to define my own <() operator for QMultiMap in order to use a custom type and define a specific values(const Key &key) behavior.

The desired behavior is to retrieve all the values that have the same group and event of the searching key (src), and the payload string that matches the initial part of the one in src. Example:

A payload in a key in my map might be: "HUB,PRESS*". If a src matches the group and event values and has the following payload:"HUB,PRESS,3" should retrieve the above element (because the src payload begin with the same string portion).

Here my implementation:

struct event_t {
    int group;
    int event;    
    QString payload;
};

inline bool operator <(const event_t &e1, const event_t &e2)
{
    if (e1.group != e2.group) return e1.group < e2.group;
    if (e1.event != e2.event) return e1.event < e2.event;

    if (e2.payload.endsWith("*\""))
    {
        qDebug() << e1.payload << e2.payload;
        QString s2 = e2.payload.mid(0, e2.payload.size() - 2);
        QString s1 = e1.payload.mid(0, s2.size());
        s1.append("\"");
        s2.append("\"");
        return s1 < s2;
    }

    return e1.payload < e2.payload;
}

Here a simple use case:

QMultiMap<event_t, event_t> m_map;
// fill with some items, one has the key like: "HUB,PRESS*"

event_t src;
// populate it

QList<event_t> dst = m_map.values(src);

The problem is I never see a debug print of src against the available items (as I expect from the values() code). Instead my qDebug() prints the same value for e1 e e2 (the one stored into my map) and never the src one. I.e.:

"\"HUB,PRESS*\"" "\"HUB,PRESS*\""

Perhaps I didn't understand how this should work?

Yes, I'm sure. To test I set it as: src.payload = "\"" + "HUB,PRESS,3" + "\""; — Mark
@StoryTeller sorry, you're right. I'm a firmware guy and I'm used to write in C... — Mark
@drescherjm that line works, I can see the qDebug() output! The problem is I cannot match the beginning of the string as in the example. — Mark

Mark Mark · Accepted Answer · 2017-10-05T16:34:31

Here the working code:

inline bool operator <(const event_t &e1, const event_t &e2)
{
    if (e1.group != e2.group) return e1.group < e2.group;
    if (e1.event != e2.event) return e1.event < e2.event;

    if (e1.payload.endsWith("*\""))
    {
        QString s1 = e1.payload.mid(0, e1.payload.size() - 2);
        QString s2 = e2.payload.mid(0, s1.size());
        s1.append("\"");
        s2.append("\"");
        return s1 < s2;
    }

    return e1.payload < e2.payload;
}

I don't know why but the src value is contained in e1 rather than e2 as I was expecting from the values() implementation.

QMap operator <()

1 Answers