Return of c++

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 towards
systems programming, why
is 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

Performance/W
Performance/T
Performance/C

Performance/$

Good timing for the new
C++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();

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

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
• Example
struct 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 error
unique_ptr<int> p3 = move(p1); // transfers ownership.
p3.reset(); // deletes the memory.
p1.reset(); // does nothing.

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

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
framework
b2 toolset=msvc-10.0 --with-test debug link=static runtime-
link=static stage
b2 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 BOOSTstagelib
– For IDE: Tools > Options > Projects > VC++ Directories > Library files
– For command line: the environment variable LIB

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