Cannot assign a vector iterator

Question

I cannot use =operator in the below code, as I am getting compiller error. I cannot understand what is wrong.

int CProcessData::calculateMidPoints(const std::vector<double>& xv, const std::vector<double>& yv)
{
    if((0 == xv.size()) || (0 == yv.size()))
        return 1;

    std::vector<double>::iterator it;

    for (it = xv.begin(); it < xv.end(); it++)
    {

    }

    return 0;
}

I am getting following error:

../src/CProcessData.cpp: In member function ‘int CProcessData::calculateMidPoints(const std::vector<double>&, const std::vector<double>&)’:
../src/CProcessData.cpp:44:9: error: no match for ‘operator=’ (operand types are ‘std::vector<double>::iterator {aka __gnu_cxx::__normal_iterator<double*, std::vector<double> >}’ and ‘__gnu_cxx::__normal_iterator<const double*, std::vector<double> >’)

I would aprichiate all help!

Answer 1

xv is a const reference, meaning only const member functions can be called in it. The const overload of std::vector<double>::begin() returns a const_iterator , and that cannot be used to construct an iterator because it would break const-coreectness.

So you need

std::vector<double>::const_iterator it;

Note that since C++11 you have other alternatives:

for (auto it = xv.begin(); it < xv.end(); it++)

or, if you're iterating over all elements, a range-based loop might be better:

for (auto x: xv) { ... // x is a copy

for (auto& x: xv) { ... // x is a reference