Question

Suppose I have the following function:

void myFunc(P& first, P& last) {
    std::cout << first.child.grandchild[2] << endl;
    // ...
}

Now, let’s assume that first.child.grandchild[2] is too long for my purposes. For example, suppose it will appear frequently in equations inside myFunc(P&,P&). So, I’d like to create some sort of symbolic reference inside the function so that my equations would be less messy. How could I do this?

In particular, consider the code below. I need to know what statement I could insert so that not only would the output from line_1a always be the same as the output from line_1b, but also so that the output from line_2a would always be the same as the output from line_2b. In other words, I don’t want a copy of the value of first.child.grandchild, but a reference or symbolic link to the object first.child.grandchild.

void myFunc(P& first, P& last) {
    // INSERT STATEMENT HERE TO DEFINE "g"

    std::cout << first.child.grandchild[2] << endl; // line_1a
    std::cout << g[2] << endl;                      // line_1b

    g[4] = X; // where X is an in-scope object of matching type

    std::cout << first.child.grandchild[4] << endl; // line_2a
    std::cout << g[4] << endl;                      // line_2b
    //...
}    

Answer 1

Say that the type of grandchild is T and size is N; then below is the way to create a reference for an array.

void myFunc(P& first, P& last) {
  T (&g)[N] = first.child.grandchild;
  ...
}

I would not prefer pointer here, though it’s also a possible way. Because, the static size of array is helpful to a static analyzer for range checking.

If you are using C++11 compiler then auto is the best way (mentioned by @SethCarnegie already):

auto &g = first.child.grandchild;