intermediate

Urbana Proposals - C++17 insight?

I've started with my series on the proposals for the next C++ Committee Meeting:

Urbana Proposals - C++17 insight?

by Jens Weller

From the article:

A short series to give you an overview over the Papers submitted in the latest mailing for the C++ Committee Meeting in Urbana-Champaign in Illinois. At the beginning of November the C++ Committee will have its 3rd Meeting this year. As C++14 is now finished, the focus is clearly on the upcoming C++17 standard.

Quick Q: Should I prefer non-member std::begin and std::end?—StackOverflow

Quick A: Yes.

A classic on SO, just re-asked yesterday:

When to use std::begin and std::end instead of container specific versions

Are there any general preferences or rules that explain when container specific versions of begin and end should be used instead of free functions std::begin and std::end?

It is my understanding that if the function is a template whereby the container type is a template parameter then std::begin and std::end should be used, i.e.:

template<class T> void do_stuff( const T& t )
{
    std::for_each( std::begin(t), std::end(t), /* some stuff */ );
}

What about in other scenarios such as a standard / member function where the type of container is known? Is it still better practice to use std::begin(cont) and std::end(cont) or should the container's member functions cont.begin() and cont.end() be preferred?

Am I correct in assuming that there is no benefit in performance by calling cont.end() over std::end(cont)?

Insights into new and C++

I've written down some basic thinking on new and new standards:

Insights into new and C++

by Jens Weller

From the article:

Every now and then, I've been thinking about this. So this blogpost is also a summary of my thoughts on this topic, dynamic memory allocation and C++. Since I wrote the blog entries on smart pointers, and C++14 giving us make_unique, raw new and delete seem to disappear from C++ in our future code...

Variadic Templates—Feabhas

variadic-templates.PNGRecently on StickyBits, a nice primer on variadics:

Variadic Templates

by feabhas

From the article:

In this article we’re going to look at a new feature of templates in C++11 -- the concept of the variadic template.

Variadic templates allow us to create functions and classes, not only with generic types, but also a variable number of generic types.

If you haven’t been following along with the template articles, I’d suggest you read this article first before continuing.

Quick Q: Can computing the length of a C string really be compile-time constexpr?—StackOverflow

Quick A: Yes, when the string being traversed is itself a constant expression, such as a string literal.

Recently on StackOverflow:

Computing length of a C string at compile time. Is this really a constexpr?

I'm trying to compute the length of a string literal at compile time. To do so I'm using following code:

#include <cstdio>

int constexpr length(const char* str)
{
    return *str ? 1 + length(str + 1) : 0;
}

int main()
{
    printf("%d %d", length("abcd"), length("abcdefgh"));
}

Everything works as expected, the program prints 4 and 8. The assembly code generated by clang shows that the results are computed at compile time:

0x100000f5e:  leaq   0x35(%rip), %rdi          ; "%d %d"
0x100000f65:  movl   $0x4, %esi
0x100000f6a:  movl   $0x8, %edx
0x100000f6f:  xorl   %eax, %eax
0x100000f71:  callq  0x100000f7a               ; symbol stub for: printf

My question: is it guaranteed by the standard that length function will be evaluated compile time?

If this is true the door for compile time string literals computations just opened for me... for example I can compute hashes at compile time and many more...

When Size Does Matter—K-Ballo

Recently on Tales of C++:

When Size Does Matter

by K-ballo

In the C++ lands every object has mass; for any complete type T, sizeof(T) is greater than zero. This keeps array indexing and pointer arithmetics from collapsing, but it also means that empty objects occupy space. Furthermore, when an empty object is placed in a class next to a bigger member, padding may — and in all likeliness will — be added due to alignment requirements, resulting in an empty member taking more than just one byte of storage.

Certainly something has to be done about this...

Lambda Over Lambda in C++14—Chris Kohlhepp

A nice complement to the C++14 lambda article we linked to yesterday:

Lambda Over Lambda in C++14: The Convergence of Modern C++ on the Lisp Programming Style, Part II

by Chris Kohlhepp

From the article:

Let us see how that simplifies under C++14 and generic lambdas.

Three observations are striking immediately:
1) The use case for a template has disappeared entirely. We simply have a generic function argument x. This matches Lisp.

2) The code is now entirely as brief as Lisp. Where Lisp has a lot of parenthesis, this style of coding develops a lot of “autos.”

3) The mechanics are identical also. Both functions are actually named lambdas...

Introduction to Type Traits in the C++ standard library—Yvonne Ma

"Are you an enum?" "Are you polymorphic?" The answers to these type questions and more are already in your C++11 standard library:

Introduction to Type Traits in the C++ standard library

by Yvonne Ma

From the article:

... As its name suggests, Type Traits exposes different characteristics of types, or simply the “type of type”. In many C++ programming practices, especially these in template metaprogramming, developers may find it difficult to build a template work for all types without knowing the characteristics of a type. That’s the key reason for the emergence of Type Trait...

C++ Templates series—Feabhas

Here's a recent series that just got a new instalment today: It introduces template basics in a nicely explained and accessible way suitable for a gentle introduction, and then going on to progressively help the reader develop stronger template muscles.

C++ Templates series

by Feabhas

An Introduction to C++ Templates

Template Classes

Template Inheritance

Templates and Polymorphism

Template Member Functions

Variadic Templates

Templates of Templates

And today: Template Specialization

From the Introduction:

Templates are a very powerful -- but often very confusing -- mechanism within C++. However, approached in stages, templates can be readily understood (despite their heinous syntax).

The aim of this series of articles is to guide beginners through the syntax and semantics of the foundation concepts in C++ template programming.