code/vector/vector_experiments.cpp

A place to experiment with vectors and see what various operations do.

                
#include <iostream>
#include <vector>

using namespace std;

ATestType is a type with copy control that also prints when its copy control members are called so we can track their usage.

                
class ATestType {
    friend ostream& operator<<(ostream& os, const ATestType& t);
 public:
    ATestType(char c, int i) : id(c), iptr(new int(i)) {}

Copy constructor: copies the storage pointed to by iptr for the new object.

                
    ATestType(const ATestType& source) {
        id = source.id;
        cout << "In ATestType copy constructor for " << id << endl;
        iptr = new int(*(source.iptr));
    }

Destructor: deletes the storage pointed to by iptr.

                
    ~ATestType() {
        cout << "In ATestType destructor for " << id << endl;
        delete iptr;
    }

    int get_val()  { return *iptr; }
    void set_val(int n)  { *iptr = n; }
 private:
    char id;
    int* iptr;
};

ostream& operator<<(ostream& os, const ATestType& t) {
    os << "|ATestType " << t.id << " has val " << *(t.iptr) << "|";
    return os;
}

Print a vector of Streamable, where Streamable must be a type that implements the stream output operator.

                
template <typename Streamable>
void print_vector(ostream& os, vector<Streamable> vec) {
    for (auto& mbr : vec) {
        os << mbr << ' ';
    }
    os << endl;
}

void section_head(const string& s) {
    cout << "\n***********************\n";
    cout << s << endl;
}

We can see that by using emplace_back() for att2, we save one call to the copy constructor.

                
int main() {
    vector<int> ivec{5, 6, 7, 8};
    print_vector(cout, ivec);

    ATestType att1{'1', 16};
    ATestType att2{'2', 32};
    vector<ATestType> att_vec;
    section_head("Pushing back att1");
    att_vec.push_back(att1);
    section_head("Emplacing back att2");
    att_vec.emplace_back(att2);

    section_head("Printing att vec");
    print_vector(cout, att_vec);
    section_head("Clearing the att vector");
    att_vec.clear();

    section_head("Exiting program");
}