Home » Blog » Tags » basics

basics

Quick Q: What does it mean to return a reference?

By Adrien Hamelin | Nov 27, 2018 02:10 PM | Tags: basics

Quick A: The returned variable can be modified.

Recently on SO:

What does it mean to return a reference?

It means you return by reference, which is, at least in this case, probably not desired. It basically means the returned value is an alias to whatever you returned from the function. Unless it's a persistent object it's illegal.

For example:

int& foo () {
    static int x = 0;
    return x;
}

//...
int main()
{
    foo() = 2;
    cout << foo();
}

would be legal and print out 2, because foo() = 2 modifies the actual value returned by foo.

However:

int& doit () {
    int x = 0;
    return x;
}

would be illegal (well, accessing the returned value would), because x is destroyed when the method exits, so you'd be left with a dangling reference.

Returning by reference isn't common for free functions, but it is for methods returning members. For example, in the std, the operator [] for common containers return by reference. For example, accessing a vector's elements with [i] returns an actual reference to that element, so v[i] = x actually changes that element.

Also, I hope that "is essentially equal to this code" means that they're semantically sort of (but not really) similar. Nothing more.

How to Retrieve the Firsts from a Collection of Pairs

By Adrien Hamelin | Nov 12, 2018 01:23 PM | Tags: basics

Simple.

How to Retrieve the Firsts from a Collection of Pairs

by Jonathan Boccara

From the article:

When using the STL, there is a use case that pops up every now and then and that often causes more trouble than necessary: if we have a collection of pairs, like an std::vector of pairs, or simply a std::map, how can we retrieve the collection of the first elements of each item in the collection?

How to Remove Elements from a Sequence Container in C++--Jonathan Boccara

By Adrien Hamelin | Sep 18, 2018 12:31 PM | Tags: basics

Using the std to remove.

How to Remove Elements from a Sequence Container in C++

by Jonathan Boccara

From the article:

As part of the STL Learning Resource, we’re tackling today the STL algorithms that remove elements from a collection.

Removing an element from a C++ collection can’t be that complicated, can it?

Well, how can I put it… It has a rich complexity, let’s say.

Ok, maybe it’s a little complicated.

We will cover this topic in a series of four articles:

  • How to Remove Elements from a Sequence Container (vector, string, deque, list)
  • How to Remove Pointers from a Vector in C++ (co-written with Gaurav Sehgal)
  • How to Remove Elements from an Associative Container (maps and sets)
  • How to Remove Duplicates from an Associative Container

C++ Weekly Episode 125: The Optimal Way To Return From A Function—Jason Turner

By Jason Turner | Jul 23, 2018 10:31 AM | Tags: performance efficiency basics

Episode 125 of C++ Weekly.

The Optimal Way To Return From A Function

by Jason Turner

About the show:

In this episode of C++ Weekly Jason investigates the possible methods that one of two string values might be returned from a function. Which option is best? Which option can the compiler optimize the most? Do we take one return path or multiple return paths? Should a ternary be used?