c++ - Operator overloading as friend function error -

i'm trying use + add 2 vector (mathematical vector). here's code:

class vector{     double v[max_size];     int dim; public:     int getdim() const;     vector();     vector(int n);     vector(const vector& a);     vector add(const vector&b);     friend vector operator+(vector summand1, vector summand2); }; 

operator overloading:

vector operator+(vector summand1, vector summand2){     int dim1 = summand1.getdim();     int dim2 = summand2.getdim();     assert(dim1 == dim2);     vector sum(dim1);     int i;     for(i = 0; < dim1; i++){         sum.v[i] = summand1.v[i] + summand2.v[i];     }     return sum; } 

and how use it:

vector m = v+t; 

when run code, shows m (0,0) (2d vector), default value generated constructor. what's wrong it? thanks!

your copy constructor:

vector::vector(const vector& a){     dim = a.dim;     vector(dim); } 

correctly sets value of dim member, has not other side effect.

you should have variant of following code:

vector::vector(const vector& a) : dim(a.dim) {     std::copy(std::begin(a.v), std::end(a.v), v); } 

this copy data present in parameter, , see correct behavior code:

// copy constructor called here, did not correctly copy data before. vector m = v + t; 

---

for better (by intend simpler , safer) vector class, if have access compiler @ least c++11 compliant, can write:

class vector{     std::array<double, max_size> v; // note std::array here.     int dim; public:     int getdim() const;     vector();     vector(int n);     vector(const vector& a);     vector add(const vector&b);     friend vector operator+(vector summand1, vector summand2); }; 

the std::array take care of everything, provided write copy constructor this:

vector::vector(const vector& a) : v(a.v), dim(a.dim) {  } 

or, better, let compiler generate copy constructor itself, same behavior.