Return of c++

Return ofC++

About Me

• Software architect in Intel since December 2005• Focused on software design and network security

before joining Intel• ~28 years since writing my first program

– Programming is fun!• A casual open-source contributor

– Several projects, but small contributions– Mostly on multi-lingual support (esp. Chinese)

• A happy father of twins

Programming languages are a fashion world. Languages come, languages go....

Do you know the August ’12 news in TIOBE

Programming Community Index?

C++ dethroned from No. 3 …

again

However, C++ is very much active, having been

active for ~30 years.

Aims of C++

• C++ makes programming more enjoyable for serious programmers.

• C++ is a general-purpose programming language that– is a better C– supports data abstraction– supports object-oriented programming– supports generic programming

Some C++ Design Rules

• C++’s evolution must be driven by real problems.• C++ must be useful now.• Don’t try to force people to use a specific

programming style.• It is more important to allow a useful feature than

to prevent every misuse.• Provide as good support for user-defined types as

for built-in types.• What you don’t use, you don’t pay for (zero

overhead rule).

C++ is biased towardssystems programming,

whyis it popular also in

applications programming?

Reason for C++ in Applications

• Performance of a specialized language

• Multiple categories in a complex application

• Language mix issue• C++ library capabilities

Better C++ Support Coming

• C++11 standardization• C++ native binding in Windows

Runtime• C++ support to mix with Objective-C• Better C++ support in Android NDK• C++11 coming to MSVC, GCC, and

Clang

Why the renaissance?

One word.

Mobile.

More words?

Performance/WPerformance/TPerformance/C

Performance/$

Good timing for the newC++11 standard....

Example

• How short can you get in C++ to dispatch work to a new thread and get the result in the current thread?

• Probably shorter than you expected:future<string> ft(async(...));...

cout << ft.get();

Examplestring flip(string s){ reverse(s.begin(), s.end()); return s;}

int main(){ vector<future<string>> v;

v.push_back(async([] { return flip( " ,olleH"); })); v.push_back(async([] { return flip("\n!letnI"); }));

for (auto& e : v) { cout << e.get(); }}

Examplestring flip(string s){ reverse(s.begin(), s.end()); return s;}

int main(){ vector<future<string>> v;

v.push_back(async([] { return flip( " ,olleH"); })); v.push_back(async([] { return flip("\n!letnI"); }));

for (auto& e : v) { cout << e.get(); }}

Examplestring flip(string s){ reverse(s.begin(), s.end()); return s;}

int main(){ vector<future<string>> v;

v.push_back(async([] { return flip( " ,olleH"); })); v.push_back(async([] { return flip("\n!letnI"); }));

for (auto& e : v) { cout << e.get(); }}

Examplestring flip(string s){ reverse(s.begin(), s.end()); return s;}

int main(){ vector<future<string>> v;

v.push_back(async([] { return flip( " ,olleH"); })); v.push_back(async([] { return flip("\n!letnI"); }));

for (auto& e : v) { cout << e.get(); }}

Compiler Compatibility

• Visual Studio 2012– Pass

• Clang 4.1 & libc++ (OS X)– Pass

• Visual Studio 2010– Range-based for and future are

unsupported• GCC 4.7.2; ICC 13.0.1 (on top of

VS2010)– future is unsupported

Incomplete List of C++11 Features

• Rvalue references and move semantics• Initializer lists• Range-based for-loop• Type inference (auto)• Lambda functions and expressions• Explicit overrides and final• Null pointer constant (nullptr)• Right angle brackets• Unicode characters and strings• Multi-threading memory model• Static assertions• Smart pointers and other standard library improvements• …

Performance

Usability

Functionality

Rvalue References and Move Semantics

• Sorry, it might be too complex for a one-pager…• Problem: copying objects (containers) can be

expensive• Key concepts: object lifecycle, temporary, lvalue,

rvalue• Key result: able to take away the object content in

a reasonable and consistent way, without surprises, via– A new reference type (&&) and related rules– Utilities to convert a type to rvalue reference type (like

std::move)– Move functions to move content to the new object and

erase the original

• Demo of destructor elimination

Initializer Lists

• C++98 allows code like this:int array[] = { 1, 2, 3, 4 };

• C++11 now allows:vector<int> v = { 1, 2, 3, 4 };

• And you can initialize your own container this way:

MyContainer::MyContainer( std::initializer_list<Type>

list){ ...}

Range-based for-loop

• Example:for (int x : { 1, 1, 2, 3, 5 })

{ cout << x << endl;}

• It implicitly calls begin() and end() on the list/array/container.

Type Inference

• Instead of writing:vector<boost::future<string> > ::iterator i = v.begin();

• One can now simply write:auto i = v.begin();

Lambdas

• Convenient where functors can be used– Say, for_each and transform

• Each lambda has a different type– So auto is handy– Class template std::function can be used to

store lambdas• Example:

FILE* fp = fopen(...);ON_SCOPE_EXIT([&]() { fclose(fp); });...

Explicit Overrides and Final

• Examplestruct Base { virtual void some(float); virtual void other();};struct Derived1 : Base { virtual void some(int) override; //

error virtual void other() final;};struct Derived2 : Derived1 { virtual void other(); // error};

Null Pointer Constant

• The definition of NULL causes surprises for:

void foo(char*);void foo(int);...foo(NULL);

• Now foo(nullptr) correctly calls foo(char*).

Right Angle Brackets

• C++98 requires an extra space here:vector<list<string> > sv;

• C++11 allows people to write:vector<list<string>> sv;

Unicode Characters and Strings

• Example:char n[] = "GCC and MSVC encode

differently: \u2018.";wchar_t w[] = L"Is it 16-bit or 32-

bit: \u2018?";

char a[] = u8"UTF-8 string: \u2018.";char16_t b[] = u"UTF-16 string: \

u2018.";char32_t c[] = U"UTF-32 string: \

u2018.";

Multi-Threading Memory Model

• Another complex topic• Memory model is defined• Standard library facilities:

– Mutexes, conditional variables, RAII locks

– Futures and promises (first example)– Atomic operations

Static Assertions

• Example:template<class T>struct Check { static_assert(sizeof(int) <= sizeof(T), "T is not big enough!");};

void DoSomething(...){ static_assert(sizeof(void*) == 4, "Supports only 32-bit platforms"); ...}

Smart Pointers

• Example:unique_ptr<int> p1(new int(5));unique_ptr<int> p2 = p1; // compile errorunique_ptr<int> p3 = move(p1); // transfers

ownership.p3.reset(); // deletes the memory.p1.reset(); // does nothing.

shared_ptr<int> p1(new int(5)); // refcount = 1shared_ptr<int> p2 = p1; // refcount = 2p1.reset(); // refcount = 1p2.reset(); // refcount = 0; frees memory

Summary

• Mobile and cloud make C++ relevant again.

• The new C++11 standard makes C++ a more powerful but easier-to-use language.– Definitely worth adopting – Especially for application developers

• Today is just an introduction.

References• ISO/IEC JTC 1/SC22: N3337 – Draft C++ Standard (very close to C++11)• Bjarne Stroustrup:

Evolving a language in and for the real world: C++ 1991-2006• Bjarne Stroustrup: An Overview of the C++ Programming Language• Scott Meyers: Summary of C++11 Feature Availability in gcc and MSVC• Wikipedia: C++11• 刘未鹏 : C++11 （及现代C++风格）和快速迭代式开发• Stephan T. Lavavej:

Lambdas, auto, and static_assert: C++0x Features in VC10, Part 1• Stephan T. Lavavej: Rvalue References: C++0x Features in VC10, Part 2• Stephan T. Lavavej: decltype: C++0x Features in VC10, Part 3• Thomas Becker: C++ Rvalue References Explained• Herb Sutter: C++ and Beyond 2011: Herb Sutter - Why C++?• Andrei Alexandrescu, Scott Meyers, Herb Sutter:

On Static If, C++11 in 2012, Modern Libraries, and Metaprogramming• Nicolai M. Josuttis: The C++ Standard Library: A Tutorial and Reference (2nd

Edition). Addison-Wesley, 2012

Backup

Poor Man’s Future – Option 1

static string tmp1() { return flip( " ,olleH"); }static string tmp2() { return flip("\n!letnI"); }

int main(){ vector<boost::future<string>> v;

v.push_back(boost::async(tmp1)); v.push_back(boost::async(tmp2));

for (auto i = v.begin(); i != v.end(); ++i) { cout << i->get(); }}

Poor Man’s Future – Option 2

int main(){ vector<boost::future<string>> v;

{ boost::packaged_task<string> pt([] { return flip( " ,olleH"); }); v.push_back(pt.get_future()); boost::thread task(boost::move(pt)); } { boost::packaged_task<string> pt([] { return flip("\n!letnI"); }); v.push_back(pt.get_future()); boost::thread task(boost::move(pt)); }

for (auto i = v.begin(); i != v.end(); ++i) { cout << i->get(); }}

Use Boost with MSVC• Most of Boost can be used without building• One needs to add the include path BOOST

– For IDE: Tools > Options > Projects > VC++ Directories > Include files

– For command line: the environment variable INCLUDE• Some components need building, like the unit

test frameworkb2 toolset=msvc-10.0 --with-test debug link=static

runtime-link=static stageb2 toolset=msvc-10.0 --with-chrono --with-date_time --

with-system --with-thread debug release link=static runtime-link=static stage

• One then needs to add the library path BOOST\stage\lib– For IDE: Tools > Options > Projects > VC++ Directories

> Library files– For command line: the environment variable LIB