why dummy value after vector opertor+? - c++

Question

I implementing vector. so i test operators, but operator+ is not working correctly.
hereis header MyDoubleVector.h
class MyDoubleVector {
public:
MyDoubleVector();
MyDoubleVector(size_t init_capacity);
MyDoubleVector(const MyDoubleVector& v);
~MyDoubleVector();
MyDoubleVector& operator=(const MyDoubleVector& v); //for deep copy
bool operator==(const MyDoubleVector& v); //binary
MyDoubleVector& operator+=(const MyDoubleVector& add);
MyDoubleVector operator[](int index); //return reference to data that requested index
MyDoubleVector operator+(const MyDoubleVector& rhs); //binary
MyDoubleVector operator-(const MyDoubleVector& rhs); //binary
MyDoubleVector operator*(const MyDoubleVector& rhs); //binary
MyDoubleVector operator-(); //unary
MyDoubleVector operator()(); //unary
void pop_back();
void push_back(double x);
size_t capacity() const;
size_t size() const;
void reserve(size_t n);
bool empty() const;
void clear();
void print_info();
private:
double *data;
size_t capa;
size_t used;
};
and here is implement code "MyDoubleVector.cpp"
MyDoubleVector MyDoubleVector::operator+(const MyDoubleVector &rhs) { //binary
//pre : same size,
//poset : return sum,
if (capa != rhs.capa) {
exit(1);
}
MyDoubleVector tmp(capa);
for (size_t i = 0; i < capa; i++) {
tmp.data[i] = data[i] + rhs.data[i];
}
return tmp;
};
and main code is
int i = 0;
MyDoubleVector v1(3);
for (i = 0; i < 4; i++) {
v1.push_back(i);
}
cout << "v1" << endl;
v1.print_info();
MyDoubleVector v2(3);
for (i = 0; i < 4; i++) {
v2.push_back(i * 10);
}
cout << "v2" << endl;
v2.print_info();
cout << "(v1+v2)" << endl;
(v1+v2).print_info();
output is
v1
0 1 2 3
used : 4, capa : 4
v2
0 10 20 30
used : 4, capa : 4
(v1+v2)
-6.27744e+66 -6.27744e+66 -6.27744e+66 -6.27744e+66
used : 0, capa : 4
i think retruned tmp is freed when print_info() function executed.
how print vector correctly?

Answer 1

You aren't setting the used of the return vector. Without seeing the rest of the implementation of the class, I guess you can change to:
MyDoubleVector MyDoubleVector::operator+(const MyDoubleVector &rhs) { //binary
//pre : same size,
//poset : return sum,
if (capa != rhs.capa) {
exit(1);
}
MyDoubleVector tmp(capa);
for (size_t i = 0; i < capa; i++) {
tmp.push_back(data[i] + rhs.data[i]);
}
return tmp;
};