if statement doesn't behave correctly

Hello all,

I came across quite unpleasant problem.
Little intro: I created templated Multiset class, suitable for use in Coloured Petri Nets, nothing fancy. As a private data holder, I'm using the QHash class.

Let's have a look on the header:

Code:

---

template<class T>
class Multiset
{
    typedef class QHash<T, uint>::iterator Iterator;
    typedef class QHash<T, uint>::const_iterator ConstIterator;
public:
    Multiset();
    virtual ~Multiset();
    ...
    Multiset<T> operator-(const Multiset<T>& other) const;
    Multiset<T> operator*(uint scalar) const;
 
    bool operator<=(const Multiset<T>& other) const;
private:
    QHash<T, uint> m_values;
};

---

I took the liberty to post only the relevant part.

Now the method definitions (methods, which doesn't behave correctly):

Code:

---

template<class T>
Multiset<T> Multiset<T>::operator-(const Multiset<T>& other) const
{
    Multiset<T> ret = *this;
 
    ConstIterator itOther = other.m_values.constBegin();
 
    if (!(ret <= other))
    {
        while (itOther != other.m_values.constEnd())
        {
            ret.m_values[itOther.key()] -= itOther.value();
            ++itOther;
        }
    }
 
    return ret;
}
...
template<class T>
bool Multiset<T>::operator<=(const Multiset<T>& other) const
{
    bool ret = false;
 
    ConstIterator itThis;
    ConstIterator itOther = other.m_values.constBegin();
 
    while (itOther != other.m_values.constEnd())
    {
        itThis = m_values.find(itOther.key());
 
        if (itThis == m_values.constEnd()
            || itThis.value() <= itOther.value())
        {
            ret = true;
            break;
        }
        ++itOther;
    }
 
    return ret;
}

---

My problem is, that no matter what the lessOrEqual operator returns, it always jumps inside the:

Code:

---

if (!(ret <= other))
    {
        while (itOther != other.m_values.constEnd())
        {
            ret.m_values[itOther.key()] -= itOther.value();
            ++itOther;
        }
    }

---

And it is causing the first series of QCOMPARE to fail in this testcase:

Code:

---

void Multiset_mt::operatorMinus()
{
    QFETCH(uint, value);
    QFETCH(uint, result);
 
    QCOMPARE(value, result);
}
 
void Multiset_mt::operatorMinus_data()
{
    const uint first_color_size = 2;
    const uint second_color_size = 1;
    const uint third_color_size = 0;
    const uint not_valid_sub_size = 0;
 
    Multiset<Color> ms1, ms2, msRes;
    Color c1("black"), c2("red"), c3("blue");
 
    ms1.insert(c1);
    ms1.insert(c2);
    ms1.insert(c2);
    ms2.insert(c1);
    ms2.insert(c2);
    ms2.insert(c3);
 
    msRes = ms1 - ms2;
 
    QTest::addColumn<uint>("value");
    QTest::addColumn<uint>("result");
 
    QTest::newRow("NOT VALID Size == 0") << msRes.size(c1) << not_valid_sub_size;
    QTest::newRow("NOT VALID Size == 0") << msRes.size(c2) << not_valid_sub_size;
    QTest::newRow("NOT VALID Size == 0") << msRes.size(c3) << not_valid_sub_size;
 
    ms1.insert(c1);
    ms1.insert(c1);
    ms2.remove(c3);
 
    msRes = ms1 - ms2;
 
    QTest::newRow("Size == 2") << msRes.size(c1) << first_color_size;
    QTest::newRow("Size == 1") << msRes.size(c2) << second_color_size;
    QTest::newRow("Size == 0") << msRes.size(c3) << third_color_size;
}

---

If anyone could help me with this, it would be really appreciated. Maybe I missed something. Thank you.

I tried to also attach the whole files.

Your code doesnt work and you think the if statement is what's wrong? ok...

Have you debugged your operator <= ?

Hello, thank you for your answer.

Actually my code does work, I've written separate module test also for operator <= and it works correctly. Of course I've debugged my code. As I'm saying, the <= returns true, bool is evaluated as false so it should not jump inside the if statement.

I also tried to create a simple stub method like:

Code:

---

bool Multiset<T>::getTrue() const
{
    return true;
}

---

and replace the bool expression with that method so it looked like:

Code:

---

if (!getTrue())
   {
        while (itOther != other.m_values.constEnd())
        {
            ret.m_values[itOther.key()] -= itOther.value();
            ++itOther;
        }
   }

---

but it jumps inside the if anyway.

Please prepare a minimal compilable example reproducing the problem.

I can tell you for a fact that your code does not work.

Line 33 of your second code block:

if you have a multiset1 with "a", "b", "b" and multiset2 with "a", "b", "c", "d" then
multiset1 <= multiset2 is true
multiset2 <= multiset1 is true

just because "a" is in both sets.

Code:

---

if (!getTrue())
   {
        while (itOther != other.m_values.constEnd())
        {
            ret.m_values[itOther.key()] -= itOther.value();
            ++itOther;
        }
   }

---

And what happens when you eliminate the method call altogether and write if ( false ) as the conditional? If it still fails to execute correctly, then I would strongly suspect that your stack is corrupted by something you did earlier on and that the failing conditional is simply an artifact.

That's why Wysota says, "Provide a minimal compilable example." You might find that in a minimal case things magically start working properly, which should be taken as a strong hint that the problem is not where you are looking.

amleto: And what is wrong with that? Operator is less OR equal. I think it returns correct result.

d_stranz: hello, yes I have tried to change the code in that way and it seems that when I use value that is known in compile time, it works correctly.

wysota: unfortunately I am away from my work computer and I am leaving for a vacation for a two weeks

so you're saying that 'less than or equal' is true if both sets have a common element? That's... strange.

to clarify:

{a,b,b,b,b} is less than or equal to {a}?

Quote:

---

unfortunately I am away from my work computer and I am leaving for a vacation for a two weeks

---

Maybe you will be lucky and the code elves will fix your program while you are away.