C++：重新崛起的巨兽

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"C++ Today: The Beast is Back" C++是一种通用的编程语言，自1983年由Bjarne Stroustrup设计以来，一直在软件开发领域占据着重要的地位。"C++ Today"这本书由Jon Kalb和Gašper Ažman合著，探讨了C++在当代的发展和应用。C++的发展历程可以被看作是编程技术的一个缩影，它经历了从早期的面向过程编程到现代的面向对象和泛型编程的转变。 C++在21世纪的今天依然活跃，部分原因在于其不断进化和适应新技术的能力。例如，C++11、C++14和C++17等标准引入了大量的新特性，包括但不限于自动类型推断（auto keyword）、lambda表达式、右值引用（rvalue references）以及并发和并行处理的支持，这些都极大地提高了C++的可读性、效率和现代软件开发的适应性。 C++11引入的lambda表达式允许程序员在需要的地方快速定义匿名函数，使得代码更加简洁和模块化。同时，自动类型推断通过减少显式的类型声明，让代码更易于理解。右值引用则是为了解决资源管理的问题，特别是对于那些生命周期短暂的对象，它们提供了更高效的方式来移动而非复制对象。 C++14和C++17继续改进和扩展了这些特性，增加了包括变量模板、std::make_unique和std::make_shared在内的功能，进一步增强了语言的灵活性和性能。此外，C++17还引入了类模板的 deduction guides，使得模板类的使用更加直观。除了语言特性，C++的标准库也在不断发展，例如线程库（<thread>）和并发工具（<future>）为多线程编程提供了强大的支持，而智能指针（如std::unique_ptr和std::shared_ptr）则帮助开发者更好地管理内存，避免了内存泄漏和悬挂指针的问题。 C++ Today这本书可能会深入讨论这些话题，以及如何在实际项目中应用这些新的语言特性和库。作者可能还会涵盖最佳实践、设计模式以及如何利用C++的优势来构建高性能和低延迟的系统。 C++ Today是针对想要了解C++最新进展和如何在当前软件开发环境中有效利用它的读者的一本宝贵资源。无论你是C++的老手还是新手，都可以从这本书中获得对C++语言新特性的深刻理解和实战技巧。

7 http://www.drdobbs.com/parallel/eliminate-false-sharing/217500206

8 For a small sample of applications and operating systems written in C++: http://

www.stroustrup.com/applications.html

general replacement for heap allocation, but in those cases where

stack allocation is acceptable, C++ programmers win by avoiding

the allocator calls.

In addition to supporting both heap allocation and stack allocation,

C++ allows programmers to construct objects at arbitrary locations

in memory. This allows the programmer to allocate buffers in which

many objects can be very efficiently created and destroyed with

great flexibility over object lifetimes.

Another example of having low-level control is in cache-aware cod‐

ing. Modern processors have sophisticated caching characteristics,

and subtle changes in the way the data is laid out in memory can

have significant impact on performance due to such factors as look-

ahead cache buffering and false sharing.

C++ offers the kind of

control over data memory layout that programmers can use to avoid

cache line problems and best exploit the power of hardware. Man‐

aged languages do not offer the same kind of memory layout flexi‐

bility. Managed language containers do not hold objects in

contiguous memory, and so do not exploit look-ahead cache buffers

as C++ arrays and vectors do.

Wide Range of Applicability

Software engineers are constantly seeking solutions that scale. This

is no less true for languages than for algorithms. Engineers don’t

want to find that the success of their project has caused it to outgrow

its implementation language.

Very large applications and large development teams require lan‐

guages that scale. C++ has been used as the primary development

language for projects with hundreds of engineers and scores of

modules.

Its support for separate compilation of modules makes it

possible to create projects where analyzing and/or compiling all the

project code at once would be impractical.

A large application can absorb the overhead of a language with a

large runtime cost, either in startup time or memory usage. But to

be useful in applications as diverse as device drivers, plug-ins, CGI

C++: What’s It Good For? | 5

9 “An incomplete list of C++ compilers”: http://www.stroustrup.com/compilers.html

10 C++ is supported on iOS, Android, Windows Mobile, and BlackBerry: http://visualstu

diomagazine.com/articles/2013/02/12/future-c-plus-plus.aspx

modules, and mobile apps, it is necessary to have as little overhead

as possible. C++ has a guiding philosophy of “you only pay for what

you use.” What that means is that if you are writing a device driver

that doesn’t use many language features and must fit into a very

small memory footprint, C++ is a viable option, where a language

with a large runtime requirement would be inappropriate.

Highly Portable

C++ is designed with a specific hardware model in mind, and this

model has minimalistic requirements. This has made it possible to

port C++ tools and code very broadly, as machines built today, from

nanocomputers to number-crunching behemoths, are all designed

to implement this hardware model.

There are one or more C++ tool chains available on almost all com‐

puting platforms.

C++ is the only high-level language alternative

available on all of the top mobile platforms.

Not only are the tools available, but it is possible to write portable

code that can be used on all these platforms without rewriting.

With the consideration of tool chains, we have moved from lan‐

guage features to factors outside of the language itself. But these fac‐

tors have important engineering considerations. Even a language

with perfect syntax and semantics wouldn’t have any practical value

if we couldn’t build it for our target platform.

In order for an engineering organization to seriously consider sig‐

nificant adoption of a language, it needs to consider availability of

tools (including analyzers and other non-build tools), experienced

engineers, software libraries, books and instructional material, trou‐

bleshooting support, and training opportunities.

Extra-language factors, such as the installed user base and industry

support, always favor C++ when a systems language is required and

tend to favor C++ when choosing a language for building large-scale

applications.

6 | Chapter 1: The Nature of the Beast

11 It would be hard to over-emphasize how costly these problems have been in non-

garbage collected languages.

Better Resource Management

In the introduction to this chapter, we discussed that other popular

languages prioritize ease of programming and safety over perfor‐

mance and control. Nothing is a better example of the differences

between these languages and C++ than their approaches to memory

management.

Most popular modern languages implement a feature called garbage

collection, or GC. With this approach to memory management, the

programmer is not required to explicitly release allocated memory

that is no longer needed. The language runtime determines when

memory is “garbage” and recycles it for reuse. The advantages to this

approach may be obvious. Programmers don’t need to track mem‐

ory, and “leaks” and “double dispose” problems

are a thing of the

past.

But every design decision has trade-offs, and GC is no exception.

One issue with it is that collectors don’t recognize that memory has

become garbage immediately. The recognition that memory needs

to be released will happen at some unspecified future time (and for

some, implementations may not happen at all—if, for example, the

application terminates before it needs to recycle memory).

Typically, the collector will run in the background and decide when

to recycle memory outside of the programmer’s control. This can

result in the foreground task “freezing” while the collector recycles.

Since memory is not recycled as soon as it is no longer needed, it is

necessary to have an extra cushion of memory so that new memory

can be allocated while some unneeded memory has not yet been

recycled. Sometimes the cushion size required for efficient operation

is not trivial.

An additional objection to GC from a C++ point of view is that

memory is not the only resource that needs to be managed. Pro‐

grammers need to manage file handles, network sockets, database

connections, locks, and many other resources. Although we may not

be in a big hurry to release memory (if no new memory is being

requested), many of these other resources may be shared with other

C++: What’s It Good For? | 7

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