Quick Q: Why does unique_ptr take two template parameters when shared_ptr only takes one? -- SO

By Blog Staff | Feb 6, 2014 05:39 AM | Tags: None

Recently on StackOverflow:

Why does unique_ptr take two template parameters when shared_ptr only takes one?

Both unique_ptr and shared_ptr accept a custom destructor to call on the object they own. But in the case of unique_ptr, the destructor is passed as a template parameter of the class, wherease the type of shared_ptr's custom destructor is to be specified as a template parameter of the constructor.

template <class T, class D = default_delete<T>>
class unique_ptr
{
    unique_ptr(T*, D&); //simplified
    ...
};

and

template<class T>
class shared_ptr
{
    template<typename D>
    shared_ptr(T*, D); //simplified
    ...
};

I can’t see why such difference. What requires that?

Quick Q: What do braces mean as a function argument? -- StackOverflow

By Blog Staff | Feb 5, 2014 03:12 AM | Tags: basics

Quick A: Something cool and convenient -- you can construct a temporary variable of the parameter type without having to repeat the type.

From SO:

C++ 11 Curly Braces

I haven't used C++ for a good few years, and have just come across this:

program.build({ default_device })

The definition is:

cl_int build(
    const VECTOR_CLASS<Device>& devices,
    const char* options = NULL,
    void (CL_CALLBACK * notifyFptr)(cl_program, void *) = NULL,
    void* data = NULL) const

What are the curly braces there for? I have never seen them used in a function call like this before. I assume it has something to do with the function pointer, but that seems optional?

Quick Q: Can a lambda refer to local variables? -- StackOverflow

By Blog Staff | Feb 4, 2014 11:32 AM | Tags: basics

Quick A: Using the [] capture list.

Yesterday on SO:

Is it possible in C++11 / 14 syntax to write an lambda function which will see parent variables?

In abstraction:

int i = 1;
auto go = [] () {
    return i;
};

Is it possible to make something like that in modern C++ syntax?

C++ Papers for Issaquah -- Concurrency

By Meeting C++ | Jan 29, 2014 07:47 AM | Tags: standardization performance intermediate experimental concurrency c++14 advanced

So I just started to read through the papers for the next C++ committee meeting in Issaquah in February, first part is about Concurrency:

C++ Papers for Issaquah -- Concurrency

by Jens Weller

From the article:

In february the C++ committee is going to meet for a week in Issaquah, it could be the final Meeting for C++14, the papers in this series will reflect both, C++14 and the standard that will come after it. Currently mostly known as C++1y. A lot of papers that are not part of C++14 will be formed into technical specifications, which some will then become C++1y later. Like the last series, I will again focus on the working groups, and post the papers sorted by the name of the working group, starting with concurrency.

Quick Q: How do I write string literals that contain special characters? -- StackOverflow

By Blog Staff | Jan 27, 2014 03:06 PM | Tags: None

Quick A: Use raw string literals! If your compiler doesn't have them yet, nag.

The original question on SO, but note the best answer is pepper_chico's rather than the selected answer:

Only Detect Text in Quotations (C++)

I'm not great at programming and recently started to read tutorials on C++.

I decided I would attempt to make a simple blackjack program. I tried to make a title with "big text" but C++ is preventing me from doing it because it is detecting other things inside the text.

    //Start Screen Begin
cout << " ____  _            _     _            _        ";
cout << "| __ )| | __ _  ___| | __(_) __ _  ___| | __    ";
cout << "|  _ \| |/ _` |/ __| |/ /| |/ _` |/ __| |/ /    ";
cout << "| |_) | | (_| | (__|   < | | (_| | (__|   <     ";
cout << "|____/|_|\__,_|\___|_|\_\/ |\__,_|\___|_|\_\    ";
cout << "                       |__/                     ";
    //Start Screen End

This is what I am trying to display, yet keep getting the following error:

undefined reference to​ 'WinMain@16'

I am asking if there is a way to tell C++ I only want it to read and display the text, and not use any functions.

C++ in 2014 -- Jens Weller

By Blog Staff | Jan 24, 2014 01:01 PM | Tags: None

From new C++ user groups springing up across Europe and upcoming conferences, to the Boost refactoring and (of course) C++14, Jens Weller has a nice piece previewing some of the things to look forward to for C++ in 2014.

C++ in 2014

by Jens Weller

Note that Jens' list is not complete, but it gives a pretty good overview of what's coming up in the near term with a few more things to be added later.

A small teaser from the article:

I already know that there are new C++ User Groups in Aachen, Dortmund, Heidelberg and Munich in Germany, also a Russian C++ User Group is now meeting in St. Petersburg and Moscow. I think a few others will follow...

Quick Q: Should "property get" functions be noexcept? -- StackOverflow

By Blog Staff | Jan 24, 2014 09:32 AM | Tags: intermediate

Quick A: Maybe, but it generally commits you to exposing the internal type (can't change representation).

Recently on SO:

Should I use noexcept for getters always?

Should I use noexcept method modifier for getters always in C++11?

I mean simple getters here that just return members. At least in all my getters I have here an exception can't possibly be thrown. One downside is that a getter gets too verbose:

const std::string& getName() const noexcept{ return name; }

The good side as pointed out in Stroustrup's book is that the compiler might do some optimizations here and there.

GotW #95 Solution: Thread Safety and Synchronization -- Herb Sutter

By Blog Staff | Jan 15, 2014 10:26 AM | Tags: intermediate

The solution to the latest GotW problem is now available:

GotW #95 Solution: Thread Safety and Synchronization

by Herb Sutter

From the article:

This GotW was written to answer a set of related frequently asked questions. So here’s a mini-FAQ on "thread safety and synchronization in a nutshell," and the points we’ll cover apply to thread safety and synchronization in pretty much any mainstream language.

Using Regular Expressions with Modern C++ -- Kenny Kerr

By Blog Staff | Jan 14, 2014 08:49 AM | Tags: intermediate

In the current MSDN Magazine:

Using Regular Expressions with Modern C++

by Kenny Kerr

From the article:

C++11 introduced a long list of features that are in themselves quite exciting, but if all you see is a list of isolated features, then you’re missing out. The combination of these features makes C++ into the powerhouse that many have grown to appreciate. I’m going to illustrate this point by showing you how to use regular expressions with modern C++... the combination of C++ language and library features really turns C++ into a productive programming language.

Quick Q: How can I avoid writing ::value and ::type when using std::enable_if? -- StackOverflow

By Blog Staff | Jan 14, 2014 06:54 AM | Tags: None

Quick A: Use a template alias. Several standard ones are coming in C++14.

Recently on SO:

How can I avoid writing ::value and ::type when using std::enable_if? [cppx]

In some of my code, namely the header rfc/cppx/text/String.h, I found the following mysterious snippet:

template< class S, class enable = CPPX_IF_( Is_a_< String, S > ) >
void operator!  ( S const& )
{ string_detail::Meaningless::operation(); }

The operator! is in support of a String class that has an implicit conversion to raw pointer. So I overload (among others) operator! for this class and derived classes, so that inadvertent use of a non-supported operator will give a suitable compilation error, mentioning that it's meaningless and inaccessible. Which I think is much preferable to such usage being silently accepted with an unexpected, incorrect result.

The CPPX_IF_ macro supports Visual C++ 12.0 (2013) and earlier, which finds C++11 using to be mostly beyond its ken. For a more standard-conforming compiler I would have written just ...

template< class S, class enable = If_< Is_a_< String, S > > >
void operator!  ( S const& )
{ string_detail::Meaningless::operation(); }

This looks like std::enable_if,

template< class S, class enabled = typename std::enable_if< Is_a_< String, S >::value, void >::type >
void operator!  ( S const& )
{ string_detail::Meaningless::operation(); }

except that the If_ or CPPX_IF_, and its expression, is much more concise and readable.

How on Earth did I do that?