call function on iterator

Question

I have a std::list of "Ray"-objects, which I want to iterate over.

for (std::list<Ray>::const_iterator it = clRay.begin(), end = clRay.end(); it != end; ++it) { *it->setDir( m_v3Position - *it->getOrigin() ) }

And the Ray objects have the methods setDir() and getOrigin():

const QVector3D &getOrigin() const { return m_v3Origin; } void setDir( const QVector3D &dir ) { m_v3Dir = dir; }

The setdir() is no problem for the compiler, but I can't call getOrigin(). Because then I get the error:

src/AreaLight.cpp: In member function ‘virtual void AreaLight::shadowFeeler(std::__cxx11::list<Ray>&, double&, ColorType&) const’: src/AreaLight.cpp:18:17: error: no match for ‘operator*’ (operand type is ‘const QVector3D’)

I think it is a const-problem, but I don't know how to fix it.

*it->setDir( m_v3Position - *it->getOrigin() ) -> it->setDir( m_v3Position - it->getOrigin() ) — RoiHatam
– RoiHatam, Commented May 4, 2017 at 23:03
Or for range: for (auto& r : clRay) { r.setDir( m_v3Position - r.getOrigin() ); } — Jarod42
– Jarod42, Commented May 4, 2017 at 23:05
if I use it->setDir( m_v3Position - it->getOrigin() ) I get the error src/AreaLight.cpp:18:47: error: passing ‘const Ray’ as ‘this’ argument discards qualifiers [-fpermissive] — heidelbeere
– heidelbeere, Commented May 4, 2017 at 23:10
If you keep to use iterator, you should not use const_iterator — Jarod42
– Jarod42, Commented May 4, 2017 at 23:16
When you code, you should understand what you do and not try random things. Obviously, you were using const_iterator and were calling setDir which is not a constant function which does not make much sense. — Phil1970
– Phil1970, Commented May 4, 2017 at 23:17

Lightness Races in Orbit · Accepted Answer · 2017-05-04 23:45:24Z

You wrote *it->. You should write just it->. There's only one level of indirection here.

This affects both calls.

In fact, the call to setDir is broken for another reason, which is that it is non-const and you are trying to get to it through a const_iterator. Adding a * doesn't fix that problem; it just masks it with a new problem. Randomly adding yet more *s, without understanding what they mean, isn't the way to go either.

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