std::weak_ptr

std::unique_ptr models the concept of exclusive ownership, std::shared_ptr the concept of shared ownership. If I stick to this picture then std::weak_ptr models the concept of temporary ownership because it borrows the resource from a std::shared_ptr. There is one dominant reason for having a std::weak_ptr in C++: breaking of cyclic references of std::shared_ptr's.

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Specialities of std::shared_ptr

After I draw the big picture of a std::shared_ptr's in the last post, I want to present two special aspects of this smart pointer in this post. First, I show with std::shared_from_this how to create a std::shared_ptr from an object; second, I'm interested in the question to the answer: Should a function take a std::shared_ptr by copy or by reference? The numbers are quite interesting.

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std::shared_ptr

std::shared_ptr's share the resource. The shared reference counter counts the number of owners. Copying a std::shared_ptr increases the reference count by one. Destroying a std::shared_ptr decreases the reference count by one. If the reference count becomes zero, the resource will automatically be released. 

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std::unique_ptr

A std::unique_ptr manages automatically and exclusively the lifetime of its resource according to the RAII idiom. std::unique_ptr should be your first choice because it does its work without memory or performance overhead.

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Memory and Performance Overhead of Smart Pointers

C++11 offers four different smart pointers. On two of them I will have a closer look in this post regarding memory and performance overhead. My first candidate std::unique_ptr takes exclusively care of the lifetime of one resource; std::shared_ptr shares the ownership of a resource with other std::shared_ptr's. I will state the result of my tests before I show you the raw numbers: There are only few reasons in modern C++ justifying the memory management with new and delete.

 

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Careful Handling of Resources

The careful handling of resources - may it be for example memory, files or sockets - is a key concern of programming in C++. This holds in particular true for the embedded programming that is often characterized by limited resources. Therefore, I will write a few posts about this challenging and versatile topic.

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Generalized Plain Old Data

Plain Old Data (POD) obeys the C standard layout. Therefore, you directly can apply the fast C functions memcopy, memmove, memset, or memcmp.

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Tags: enum
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Buckets, Capacity, and Load Factor

The hash function maps a potential infinite number of keys on a finite number of buckets. What is the strategy of the C++ runtime and how can you tailor it to your needs, that is what this article is all about.

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Hash Functions

The reason for the constant access time (best cast) of the unordered associative containers are the hash functions. As ever, C++ offers a lot of ways to adjust the behaviour of the hash functions. On one hand, C++ has a lot of different hash functions; on the other hand, you can define your own hash function. You can even adjust the number of buckets.

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Associative Containers - A simple Performance Comparison

Before I take a deeper look insight the interface of the hash tables - officially called unordered associative containers - I will at first compare the performance of the associative containers. The best candidates are std::unordered_map and the ordered pendant std::map because both are used most frequently.

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