friend ostream & operator <<(ostream &output, const Vector &);
如果去掉 const 会编译错误 为什么?
下面贴代码
class Vector
{
public:
Vector(int size);
Vector(double *, int);
~Vector();
double &operator;
Vector & operator =(Vector &);
friend Vector operator +(Vector &, Vector &);
friend Vector operator - (Vector &, Vector &);
friend double operator *(Vector &, Vector &);
friend ostream & operator <<(ostream &output, const Vector &);
friend istream & operator >> (istream &input, Vector &);
private:
double *v;
int len;
};
ostream & operator<<(ostream &output, const Vector & a)
{
output << "(";
for (int i = 0; i < a.len - 1; i++) output << a.v[i] << ",";
output << a.v[a.len - 1] << ")";
return output;
}
年轻的程序猿求大神赐教