call of overloaded 'qHash(const double&)' is ambiguous

I get this error when I try to convert a QList to a QSet.

QList<double> x_pts;
x_pts << 4.1;
x_pts &开发者_运维知识库lt;< 2.2;
x_pts << 2.2;
x_pts << 1.3;
qSort(x_pts);
QSet<double> list = x_pts.toSet();

Any idea why i am getting this error? It works fine if I change the type to int or double*. But double should work as well.

All i want to do is to remove duplicates from my list. I want to find a way to do it without iterating the list myself.

Any help in removing this error or another function to remove duplicates will be appreciated.

Thanks,

Rush

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The compiler error is due to the fact that Qt simply hasn't defined a qHash() function that takes in a double. The reason for this is that it is generally a bad idea to use floating point numbers as keys in a hash (in this case your QSet uses a hash internally).

You say you are trying to remove duplicates, but the concept of equality among floating point numbers is fuzzy in C++, as it turns out to be quite difficult to say that any two floating point numbers are truly equal.

(See the C++ faq regarding this subject)

The solution to your problem is going to be either:

a) Don't use floating point numbers

b) Define your own qHash function that satisfies the requirements of your program in a way that is satisfactory. Defining a qHash( double ) in your implentation file would be sufficient.