Although some people regard C++ as the COBOL of the 21st century, it remains a force to be reckoned with in commercial development. For example it is currently ranked fourth in the language related tags on stackoverflow.com (despite the apparent biases of Stackoverflow owners Jeff Atwood and Joel Spolsky towards web and .Net oriented languages):

Rank Language Tagged questions 1 C# 4681 2 Java 2903 3 ASP.Net 2334 4 C++ 2040 5 Javascript 1677 6 PHP 1505 7 Python 1397 8 C 851 9 Ruby 719 10 VB.Net 548

C++ has been one of the top commercial languages for a long time. But the world of computer software and hardware is changing fast and languages have to evolve to stay relevant. The first major revision to the C++ standard in a decade, known as C++ 0x, is expected be finalised in 2009 (otherwise the x will have to be hex). The draft standard includes lots of additions to the language and standard libraries, including: lambdas; closures; static (compile time) asserts; concepts; automatic types; variadic templates; a regular expressions library and improved threading support. Automatic garbage collection is notable by its absence.

For working C++ developers the new standard only really becomes important when it becomes available in mainstream compilers such as Visual C++ and Gnu C++. As Gnu C++ already has experimental support for C++ 0x and Microsoft released a preview of Visual Studio 2010 at PDC last month with support for some of new features it might be a good time to start paying attention to the new standard. You don’t want to look like an idiot next time one your colleagues starts talking about ‘lambdas’, do you?

I illustrate a few of the new features below. I have done this mainly as a way of understanding them better myself, not because I claim any sort of expertise on the new standard.

Lambdas and closures

A ‘lambda’ is an unnamed function, for example:

std::vector<int> values = getValues();

std::for_each( values.begin(), values.end(), [](int n) { cout << n << std::endl; } );

Lambdas can reference in-scope variables, for example:

std::vector<int> values = getValues();

int total = 0;

std::for_each( values.begin(), values.end(), [&total](int n) { total += n } );

This is known as a ‘closure’. Of course, all of this can be done with standard function calls, but lambdas are undoubtedly more compact and elegant. I am not convinced that they will make code any clearer or easier to debug or maintain however.

Automatic types

Automatic typing allows the compiler to infer a type. For example:

std::vector<int> values = getValues();

for ( std::vector<int>::const_iterator it = values.begin(); it != values.end(); ++it ) { f( it ); }

Can be re-written as:

auto values = getValues();

for ( auto it = values.begin(); it != values.end(); ++it ) { f( it ); }

Automatic types seem like an excellent way to let the compiler take some of the drudgery out of programming.



Concepts

Template error messages have improved over the years, but they can still be obscure. A ‘concept’ is a way to clearly define what types a templated class or function will accept. For example:

template<typename T> requires LessThanComparable<T>

const T& min(const T &x, const T &y)

{

return y < x ? y : x;

}

Specifies that min() will only accept types that support the concept LessThanComparable. LessThanComparable can then be defined so that the type must support the < operator:

auto concept LessThanComparable<typename T>

{

bool operator<(T, T);

}

Hopefully concepts will allow better defined template interfaces and clearer error messages.

Concurrency

The current C++ standard makes no real allowances for concurrency. This is a major problem in a world where multi-core CPUs are standard. The new standard will introduce a memory model that supports threading and a standard threading library.

Summary

C++ has many strengths. It scores quite highly on performance, expressiveness and portability, has an extensive tool and library ‘ecosystem’ and a proven track record in large scale system development. But it is also a sprawling and complex language, hobbled by many shortcomings inherited from its progenitor C (a language dating back to the early seventies). It isn’t clear to me whether the new standard will add enough features to keep C++ competitive as a commercial language for another decade. Or whether C++ will be regarded as a legacy language, too bloated and complex to attract new developers given the choice of simpler and more elegant languages. Time will tell.

Further reading:

C++ 0x article on wikipedia