Specifying template parameters
I want to write my own vector class and function that calculates the cross product.
My class vector has
template<class T, int dim, bool isRowVector>
T is the record type, dim size and isRowVector determines whether the vector is a row or a column vector.
I have overloaded some Vector operators, in particular <lt ;:
template <class T, int dim, bool isRowVec>
std::ostream& operator<<(std::ostream& os, Vector<T, dim, isRowVec>& vec) // <<
{
os << "[" << vec[0];
for(typename std::vector<T>::iterator it = vec.begin()+1; it != vec.end(); it++) {
os << "," << *it;
}
os << "]";
if(!isRowVec) { os << "^T"; }
return os;
}
Now the crossProduct function should only be applied to vectors with dim = 3. So I set a function like this:
template <class T, bool isRowVec>
Vector<T, 3, isRowVec> crossProduct (Vector<T, 3, isRowVec> a, Vector<T, 3, isRowVec> b) {
T arr[3] = { a[1]*b[2]-a[2]*b[1], a[2]*b[0]-a[0]*b[2], a[0]*b[1]-a[1]*b[0] };
Vector<T, 3, isRowVec> newVec(arr);
return newVec;
}
excluding the dim parameter in the function template, as it doesn't need to be guessed or specified.
This does not seem to be a problem since
Vector<float,3,true> a = crossProduct(f,g);
does not generate a compilation error where f and g are both
Vector<float,3,true>
But when I try to call
std::cout << crossProduct(f, g) << std::endl;
I get
error: no match for 'operator<<' (operand types are 'std::ostream {aka std::basic_ostream<char>}' and 'Vector<float, 3, true>')
std::cout << crossProduct(f, g) << std::endl;
^
Any ideas?
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2 answers
std::cout << crossProduct(f, g) << std::endl;
|
|
+------Creates a temporary object (rvalue)
rvalues cannot bind to non-const references, so use reference const
instead
template <class T, int dim, bool isRowVec>
std::ostream& operator<<(std::ostream& os, const Vector<T, dim, isRowVec>& vec)
// ~~~~~
{
// ....
}
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