Strict Weak Ordering and STL—Saurabh Singh

Saurabh Singh describes in a brief tutorial on how to correctly implement the comparator function for STL containers and algorithms. 

Strict Weak Ordering and STL

by Saurabh Singh

From the article:

If you had ever used a map or set or even std::sort I bet you would have to give a comparator function. (Or an overload to the < (less than) operator).
I will try to give an overview of how certain associative stl containers use this property for ordering the elements.
Almost all stl containers rely on strict weak ordering A strict weak ordering defines the relative position of elements in terms of precedence of one item over other. For eg. if you have a room full of person and you have to form a queue based on their height, a person with "lesser" height will "precede" the person with greater height. For a function to be satisfying strict weak ordering following conditions need to be met.

The PDF version of the document is available here.

Quick Q: Need of a weak_ptr in C++11

Quick A: To keep a pointer on a ressource without owning it.

Recently on SO:

Need of a weak_ptr in C++11

The second half of that statement should be clear: if a pointer is not an owning pointer then the object it is pointing at might be deleted by whatever software is the owner - and then you'd have the standard dangling reference.

So this issue is: you've got objects owned by some piece of software which is letting other software have access to it - but the other software won't share the ownership. So the owner can delete it at any time and the other software needs to know it's pointer is no longer valid.

Maybe an example would help:

You've got some piece of software watching a camera pointing out your window to a bird feeder and it is identifying birds at the feeder, which come and go. Each bird at the feeder has an object created by this software when it arrives at the feeder, and the object is deleted when the bird flies away.

Meanwhile, some other software it taking a census. Every 10 seconds it grabs from the feeder-watching software a collection of the birds at the feeder. Every 100 seconds it emits a report of which birds were at the feeder for the entire 100 seconds.

Because the data for a bird is big the census-taker doesn't copy the data. It merely gets, every 10 seconds, a collection of pointers from the feeder-watcher.

To make it necessary to use weak pointers, let's say the feeder-watcher only provides pointers to birds which have arrived in the last ten seconds, not the ones which have been there. That is, there is no notification that birds have disappeared.

By using weak pointers it can know, at report time, which of the birds are still there, and when they arrived (but not when they left).

(Maybe I'll think of a better example later.)

The Ultimate Question of Programming, Refactoring, and Everything

Yes, you've guessed correctly - the answer is "42". In this article you will find 42 recommendations about coding in C++ that can help a programmer avoid a lot of errors, save time and effort.

The Ultimate Question of Programming, Refactoring, and Everything

by Andrey Karpov

From the article:

The scope of my interests − the C/C++ language and the promotion of code analysis methodology. I have been Microsoft MVP in Visual C++ for 5 years. The main aim of my articles and work in general - is to make the code of programs safer and more secure. I'll be really glad if these recommendations help you write better code, and avoid typical errors. Those who write code standards for companies may also find some helpful information here.

Safe Clearing of Private Data

We often need to store private data in programs, for example passwords, secret keys, and their derivatives, and we usually need to clear their traces in the memory after using them so that a potential intruder can't gain access to these data. In this article we will discuss why you can't clear private data using memset() function.

Safe Clearing of Private Data

by Roman Fomichev

From the article:

So, both gcc and clang decided to optimize our code. Since the memory is freed after calling the memset() function, the compilers treat this call as irrelevant and delete it.

Guidelines Support Library Review: string_span—Marius Bancila

What is a string_span?

Guidelines Support Library Review: string_span<T>

by Marius Bancila

From the article:

In a previous post I have introduced the span<T> type from the Guidelines Support Library. This is a non-owning range of contiguous memory recommended to be used instead of pointers (and size counter) or standard containers (such as vector or array). span<T> can be used with strings, but the Guidelines Support Library provides a different span implementation for various types of strings. These string span types are available in the string_span.h header.