Does Object Slicing Occur When Using a `vector` in C ?

Vectors and Polymorphism in C : Object Slicing

Consider the following C code:

<code class="cpp">class Instruction {
public:
    virtual void execute() { }
};

class Add: public Instruction {
private:
    int a;
    int b;
    int c;
public:
    Add(int x, int y, int z) {a=x;b=y;c=z;}
    void execute() { a = b + c;  }
};</code>

In a separate class:

<code class="cpp">void some_method() {
    vector<Instruction> v;
    Instruction* i = new Add(1,2,3)
    v.push_back(*i);
}</code>

And in another class:

<code class="cpp">void some_other_method() {
    Instruction ins = v.back();
    ins.execute();
}</code>

These classes share the Instruction vector. However, we encounter a concern regarding the execute function. Will it retain its Add type?

Unfortunately, it will not. vector stores values, not references. This means the Instruction object will be copied at some point, leading to a phenomenon called "object slicing."

To resolve this issue, consider using vector or, more effectively, vector< std::reference_wrapper >.

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