error: no match for ‘operator=’

[Chrisj]

I'm writing a small openGL program to do keyframe animation. The lines of code I have highlighted in my code appear responsible for the error I get when compiling (full output below).

I'd like to know why this is wrong, and also any suggestions as to how to do it differently.

Cheers, Chris

class Vector3f {
	float _item[3];
	public: //.......
// Vector3f is just a simple array of floats with a rotation function.
// I don't think it's relevant to this problem.
}


struct Keyframe{
    int frameid;
    Vector3f rotation;
};

struct AnimTrack {
    int trackid;
    vector <Keyframe>  _keyFrames;
};



class Animation {
    int numFrames;
    int currentFrame;
    int numJoints;
    
    vector <AnimTrack> _tracks;   
    
public:
    Animation(){};
    
    void setNumFrames(int frames){ numFrames = frames;}
    
    int getNumFrames() {return numFrames;}
   
    int getnumJoints(){return numJoints;} 
    
    void addAnimtrack(AnimTrack &track){
         _tracks.push_back(track);
    }        
};

error:
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algobase.h: In static member function ‘static _OI std::__copy<_BoolType, std::random_access_iterator_tag>::copy(_II, _II, _OI) [with _II = const Keyframe*, _OI = Keyframe*, bool _BoolType = false]’:
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algobase.h:317: instantiated from ‘_OI std::__copy_aux(_II, _II, _OI) [with _II = const Keyframe*, _OI = Keyframe*]’
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algobase.h:354: instantiated from ‘static _OI std::__copy_normal<true, true>::copy_n(_II, _II, _OI) [with _II = __gnu_cxx::__normal_iterator<const Keyframe*, std::vector<Keyframe, std::allocator<Keyframe> > >, _OI = __gnu_cxx::__normal_iterator<Keyframe*, std::vector<Keyframe, std::allocator<Keyframe> > >]’
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algobase.h:387: instantiated from ‘_OutputIterator std::copy(_InputIterator, _InputIterator, _OutputIterator) [with _InputIterator = __gnu_cxx::__normal_iterator<const Keyframe*, std::vector<Keyframe, std::allocator<Keyframe> > >, _OutputIterator = __gnu_cxx::__normal_iterator<Keyframe*, std::vector<Keyframe, std::allocator<Keyframe> > >]’
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/vector.tcc:152: instantiated from ‘std::vector<_Tp, _Alloc>& std::vector<_Tp, _Alloc>::operator=(const std::vector<_Tp, _Alloc>&) [with _Tp = Keyframe, _Alloc = std::allocator<Keyframe>]’
anim.h:197: instantiated from ‘void std::vector<_Tp, _Alloc>::_M_insert_aux(__gnu_cxx::__normal_iterator<typename std::_Vector_base<_Tp, _Alloc>::_Tp_alloc_type::pointer, std::vector<_Tp, _Alloc> >, const _Tp&) [with _Tp = AnimTrack, _Alloc = std::allocator<AnimTrack>]’
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_vector.h:610: instantiated from ‘void std::vector<_Tp, _Alloc>::push_back(const _Tp&) [with _Tp = AnimTrack, _Alloc = std::allocator<AnimTrack>]’
anim.h:221: instantiated from here
/usr/lib/gcc/i386-redhat-linux/4.1.2/../../../../include/c++/4.1.2/bits/stl_algobase.h:285: error: no match for ‘operator=’ in ‘* __result = * __first’
anim.h:192: note: candidates are: Keyframe& Keyframe::operator=(Keyframe&)

[jsmith]

What else is in struct Keyframe and Vector3f?

[Chrisj]

There is nothing else in Keyframe at present, this is the full Vector3f Class

class Vector3f {

	float _item[3];

	public:

	float & operator [] (int i) {
		return _item[i];
    	}

	Vector3f(float x, float y, float z) 
	{  _item[0] = x ; _item[1] = y ; _item[2] = z; };

	Vector3f() {};


	Vector3f & operator = (Vector3f & obj) 
	{
		_item[0] = obj[0];
		_item[1] = obj[1];
		_item[2] = obj[2];

		return *this;
	};

	Vector3f & operator += (Vector3f & obj) 
	{
		_item[0] += obj[0];
		_item[1] += obj[1];
		_item[2] += obj[2];

		return *this;
	};
	
	//Eulerian rotation about X, Y, and Z axes in that order.
	void rotateXYZ(float angleX, float angleY, float angleZ, Vector3f & center){
		float offset[3];
		float ret[3];
		
		offset[0]=_item[0]-center[0];
		offset[1]=_item[1]-center[1];
		offset[2]=_item[2]-center[2];
		
		
		//Rotate around X
		ret[0] = offset[0];
		ret[1] = offset[1]*cos(angleX) + offset[2]*sin(angleX);
		ret[2] = offset[2]*cos(angleX) - offset[1]*sin(angleX);
		
		//Rotate around Y
		_item[0] = ret[0]*cos(angleY) - ret[2]*sin(angleY);
		_item[1] = ret[1];
		_item[2] = ret[0]*sin(angleY) + ret[2]*cos(angleY);
	
		//Rotate around Z
		ret[0] = _item[0]*cos(angleZ) + _item[1]*sin(angleZ);
		ret[1] = _item[1]*cos(angleZ) - _item[0]*sin(angleZ);
		ret[2] = _item[2];

		_item[0] = ret[0]+center[0];
		_item[1] = ret[1]+center[1];
		_item[2] = ret[2]+center[2];
	};
};

[Chrisj]

I managed to find someone who could help me on this one. Here's the fix:

Changed _tracks to be a vector of pointers to AnimTracks, and changed addAnimtrack take a pointer as a parameter.

class Animation {
    int numFrames;
    int currentFrame;
    int numJoints;
    
    vector <AnimTrack *> _tracks;   
    
public:
    Animation(){};
    
    void setNumFrames(int frames){ numFrames = frames;}
    
    int getNumFrames() {return numFrames;}
   
    int getnumJoints(){return numJoints;} 
    
    void addAnimtrack(AnimTrack* track){
         _tracks.push_back(track);
    }        
};

[jsmith]

You didn't fix the problem, you masked it.

Try changing Vector3f's assignment operator to a more correct declaration:

Vector3f& operator=( const Vector3f& rhs ) { /* ... */ }

and see if that fixes the compile error.

[Chrisj]

I changed the operator as you suggested, and it works fine now. I'm still not entirely sure why the const makes such a difference, so i'm back to my books to find out.

Cheers.

[jsmith]

Because there is a little clause in the standard that says you cannot bind temporaries to non-const references. A simple example:

#include <string>
#include <iostream>

using namespace std;

void print_me( string& s ) {
    cout << s << endl;
}

int main() {
   print_me( string( "Hello World" ) );
}

generates a compile error because the string( "Hello World" ) is a
temporary object that is being passed to a function that accepts a (non-const)
reference. To fix the compile error, print_me should take its parameter by const
reference. The standard allows for temporaries to be bound to const references.

This is exactly the problem you were having.