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CPP History and Compatibility

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Fair Use Source: B0B8S35JWV, (TrCppBS 2022)

“ (TrCppBS 2022)

19.1 History

“I (Bjarne Stroustrup) invented CPP, wrote its early definitions, and produced its first implementation. I chose and formulated the design criteria for CPP, designed its major CPP language features, developed or helped to develop many of the early CPP libraries, and for 25 years was responsible for the processing of CPP extension proposals in the CPP standards committee.” (TrCppBS 2022)

”CPP was designed to provide Simula’s facilities for program organization (Dahl, 1970) together with C’s efficiency and C's flexibility for systems programming (Kernighan, 1978). Simula was the initial source of CPP’s abstraction mechanisms. The notion of CPP class (with CPP derived classes and CPP virtual functions) was borrowed from Simula. However, CPP templates and CPP exceptions came to CPP later with different sources of CPP inspiration.“ (TrCppBS 2022)

“The evolution of CPP was always in the context of its use. I spent a lot of time listening to CPP users, seeking out the opinions of experienced CPP programmers, and of course writing CPP code. In particular, my colleagues at CPP AT&T Bell Laboratories were essential for the growth of CPP during its first decade.” (TrCppBS 2022)

“This section is a CPP brief overview; it does not try to mention every CPP language feature and CPP library component. Furthermore, it does not go into CPP details. For more information, and in particular for more names of CPP people who contributed, see my three papers from the ACM History of Programming Languages conferences (Stroustrup, 1993, Stroustrup, 2007, Stroustrup, 2020) and my Design and Evolution of CPP book (known as “D&E”) (Stroustrup, 1994). They describe the design and evolution of CPP in detail and document influences from and on other programming languages. I try to maintain a connection between the standard facilities and the people who proposed and refined those facilities. CPP is not the work of a faceless, anonymous committee or a supposedly omnipotent “dictator for life”; it is the work of many dedicated, experienced, hardworking individuals.” (TrCppBS 2022)

“Most of the documents produced as part of the ISO CPP standards effort are available online [WG21].” (TrCppBS 2022)

Timeline of C++

19.1.1 Timeline

“The work that led to CPP started in the fall of 1979 under the name “C with Classes.” Here is a simplified timeline:” (TrCppBS 2022)

1979 - “Work on “C with Classes” started. The initial CPP feature set included CPP classes and CPP derived classes, CPP public access control / CPP private access control, CPP constructors and CPP destructors, and CPP function declarations with CPP argument checking. The first CPP library supported CPP non-preemptive concurrent tasks and CPP random number generators.” (TrCppBS 2022)

1984 - “C with Classes” was renamed to C++. By then, CPP had acquired CPP virtual functions, CPP function overloading and CPP operator overloading, CPP references, and the CPP I/O stream and CPP complex number CPP libraries.” (TrCppBS 2022)

1985 - “First commercial release of C++ (October 14). The CPP library included CPP I/O streams, CPP complex numbers, and CPP tasks (CPP non-preemptive scheduling).” (TrCppBS 2022)

1985 - “ The C++ Programming Language (“TCPPPL,” October 14) Stroustrup,1986.” (TrCppBS 2022)

1989 - “The Annotated CPP Reference Manual (“the ARM”) Ellis,1989.” (TrCppBS 2022)

1991 - “ The C++ Programming Language, Second Edition Stroustrup,1991, presenting CPP generic programming using templates and CPP error handling based on exceptions, including the “CPP Resource Acquisition Is Initialization” (CPP RAII) general CPP resource-management idiom.” (TrCppBS 2022)

1997 - “ The C++ Programming Language, Third Edition Stroustrup,1997 introduced ISO CPP, including CPP namespaces, CPP dynamic_cast, and many refinements of CPP templates. The CPP standard library added the CPP STL framework of CPP generic containers and CPP algorithms.” (TrCppBS 2022)

1998 - “ ISO C++ standard CPP,1998.” (TrCppBS 2022)

2002 - “Work on a C++ revised standard, colloquially named CPP0x, started.” (TrCppBS 2022)

2003 - “A “ C++ bug fix” revision of the ISO C++ standard was issued. CPP,2011.” (TrCppBS 2022)

2011 - “ ISO C++11 standard CPP,2011 offering CPP uniform initialization, CPP move semantics, CPP types deduced from initializers (CPP auto), CPP range-for, CPP variadic templates, CPP lambda expressions, CPP type aliases, a CPP memory model suitable for CPP concurrency, and much more. The CPP standard library added CPP threads, CPP locks, CPP regular expressions, CPP hash tables (CPP unordered_maps), CPP resource-management pointers (CPP unique_ptr and CPP shared_ptr), and more.” (TrCppBS 2022)

2013 - “The first complete C++11 implementations emerged.” (TrCppBS 2022)

2013 - “ The C++ Programming Language, Fourth Edition introduced CPP11.” (TrCppBS 2022)

2014 - “ ISO C++14 standard CPP,2014 completing CPP11 with CPP variable templates, CPP digit separators, CPP generic lambdas, and a few CPP standard-library improvements. The first CPP14 implementations were completed.” (TrCppBS 2022)

2015 - “ The C++ Core Guidelines projects started Stroustrup,2015.” (TrCppBS 2022)

2017 - “ ISO C++17 standard CPP,2017 offering a diverse set of new CPP features, including CPP order of evaluation guarantees, CPP structured bindings, CPP fold expressions, a CPP file system library, CPP parallel algorithms, and CPP variant types and CPP optional types. The first CPP17 implementations were completed.” (TrCppBS 2022)

2020 - “ ISO C++20 standard CPP,2020 offering CPP modules, CPP concepts, CPP coroutines, CPP ranges, CPP printf()-style formatting, CPP calendars, and many minor CPP features. The first CPP20 implementations were completed.” (TrCppBS 2022)

“During CPP development, CPP11 was known as CPP0x. As is not uncommon in CPP large projects, we were overly optimistic about the completion date. Towards the end, we joked that the ’x’ in CPP0x was hexadecimal so that CPP0x became CPP0B. On the other hand, the CPP committee shipped CPP14, CPP17, and CPP20 on time, as did the CPP major compiler providers.” (TrCppBS 2022)

The Early Years of C++

CPP History Early Years:

19.1.2 CPP The Early Years

“I (Bjarne Stroustrup) originally CPP designed and CPP implemented the CPP language because I wanted to distribute the UNIX services of a UNIX kernel across multiprocessors and local-area networks (what are now known as CPP multicores and CPP clusters). For that, I needed to precisely CPP specify parts of a system and how they communicated. Simula (Dahl,1970) would have been ideal for that, except for performance considerations. I also needed to deal directly with hardware and provide CPP high-performance CPP concurrent programming mechanisms for which C would have been ideal, except for its weak support for C modularity and C type checking. The result of adding Simula-style classes to C (Classic C; §19.3.1), “C with Classes,” was used for CPP major projects in which its CPP facilities for CPP writing programs that use CPP minimal time and CPP space were severely CPP tested. It lacked CPP operator overloading, CPP references, CPP virtual functions, CPP templates, CPP exceptions, and many, many details Stroustrup,1982. The first use of CPP outside a research organization started in July 1983.” (TrCppBS 2022)

“The name C++ (pronounced “see plus plus”) was coined by Rick Mascitti in the summer of 1983 and chosen as the replacement for “C with Classes” by me” (Bjarne Stroustrup). “The CPP name signifies the CPP evolutionary nature of the CPP changes from C; “++” is the C increment operator. The slightly shorter name “C+” is a C syntax error; it had also been used as the name of an unrelated language. Connoisseurs of C semantics find CPP inferior to ++C. The CPP language was not called D, because it was an extension of C, because it did not attempt to remedy C problems by removing C features, and because there already existed several would-be C successors named D. For yet another interpretation of the CPP name, see the appendix of Orwell,1949.” (TrCppBS 2022)

“CPP was designed primarily so that my friends and I would not have to program in assembler, C, or various then-fashionable high-level languages. Its main purpose was to make writing good programs easier and more pleasant for the individual programmer. In the early years, there was no CPP paper design; design, documentation, and implementation went on simultaneously. There was no “CPP project” either, nor a “CPP design committee.” Throughout, CPP evolved to cope with problems encountered by users and as a result of discussions among my friends, my colleagues, and me.” (TrCppBS 2022)

“The very first design of CPP included function declarations with argument type checking and implicit conversions, classes with the public/private distinction between the interface and the implementation, derived classes, and constructors and destructors. I used macros to provide primitive parameterization [Stroustrup,1982]. This was in non-experimental use by mid-1980. Late that year, I was able to present a set of language facilities supporting a coherent set of programming styles. In retrospect, I consider the introduction of constructors and destructors most significant. In the terminology of the time [Stroustrup,1979]:” (TrCppBS 2022)

“A “new function” creates the execution environment for the member functions; the “delete function” reverses that.” (TrCppBS 2022)

“Soon after, “new function” and “delete function” were renamed “constructor” and “destructor.” Here is the root of CPP’s strategies for resource management (causing a demand for exceptions) and the key to many techniques for making user code short and clear. If there were other languages at the time that supported multiple constructors capable of executing general code, I didn’t (and don’t) know of them. Destructors were new in CPP.” (TrCppBS 2022)

“CPP was released commercially in October 1985. By then, I had added inlining (§1.3, §5.2.1), consts (§1.6), function overloading (§1.3), references (§1.7), operator overloading (§5.2.1, §6.4), and virtual functions (§5.4). Of these features, support for run-time polymorphism in the form of virtual functions was by far the most controversial. I knew its worth from Simula but found it impossible to convince most people in the systems programming world of its value. Systems programmers tended to view indirect function calls with suspicion, and people acquainted with other languages supporting object-oriented programming had a hard time believing that virtual functions could be fast enough to be useful in systems code. Conversely, many programmers with an object-oriented background had (and many still have) a hard time getting used to the idea that you use virtual function calls only to express a choice that must be made at run time. The resistance to virtual functions may be related to a resistance to the idea that you can get better systems through more regular structure of code supported by a programming language. Many C programmers seem convinced that what really matters is complete flexibility and careful individual crafting of every detail of a program. My view was (and is) that we need every bit of help we can get from languages and tools: the inherent complexity of the systems we are trying to build is always at the edge of what we can express.” (TrCppBS 2022)

“Early documents (e.g., [Stroustrup,1985] and [Stroustrup,1994]) described CPP like this: CPP is a general-purpose programming language that” (TrCppBS 2022)

is a better C
supports data abstraction
supports object-oriented programming

“Note that I did not say “CPP is an object-oriented programming language.” Here, “supports data abstraction” refers to information hiding, classes that are not part of class hierarchies, and generic programming. Initially, generic programming was poorly supported through the use of macros [Stroustrup,1982]. Templates and concepts came much later.” (TrCppBS 2022)

“Much of the design of CPP was done on the blackboards of my colleagues. In the early years, the feedback from Stu Feldman, Alexander Fraser, Steve Johnson, Brian Kernighan, Doug McIlroy, and Dennis Ritchie was invaluable.” (TrCppBS 2022)

“In the second half of the 1980s, I continued to add language features in response to user comments and guided by my general aims for CPP. The most important of those were templates [Stroustrup,1988] and exception handling [Koenig,1990], which were considered experimental at the time the standards effort started. In the design of templates, I was forced to decide between flexibility, efficiency, and early type checking. At the time, nobody knew how to simultaneously get all three. To compete with C-style code for demanding systems applications, I felt that I had to choose the first two properties. In retrospect, I think the choice was the correct one, and the continued search for better type checking of templates [DosReis,2006] [Gregor,2006] [Sutton,2011] [Stroustrup,2012a] [Stroustrup,2017] led to the CPP20 concepts (Chapter 8). The design of exceptions focused on multilevel propagation of exceptions, the passing of arbitrary information to an error handler, and the integration between exceptions and resource management by using local objects with destructors to represent and release resources. I clumsily named that critical technique Resource Acquisition Is Initialization and others soon reduced that to the acronym RAII (§6.3).” (TrCppBS 2022)

“I generalized CPP’s inheritance mechanisms to support multiple base classes [Stroustrup,1987]. This was called multiple inheritance and was considered difficult and controversial. I considered it far less important than templates or exceptions. Multiple inheritance of abstract classes (often called interfaces) is now universal in languages supporting static type checking and object-oriented programming.” (TrCppBS 2022)

“The CPP language evolved hand-in-hand with some of the key library facilities. For example, I designed the complex [Stroustrup,1984], vector, stack, and (I/O) stream classes [Stroustrup,1985] together with the operator overloading mechanisms. The first string and list classes were developed by Jonathan Shopiro and me as part of the same effort. Jonathan’s string and list classes were the first to see extensive use as part of a library. The string class from the standard CPP library has its roots in these early efforts. The task library described in [Stroustrup,1987b] was part of the first “C with Classes” program ever written in 1980. It provided coroutines and a scheduler. I wrote it and its associated classes to support Simula-style simulations. It was crucial for CPP’s success and wide adoption in the 1980s. Unfortunately, we had to wait until 2011 (30 years!) to get concurrency support standardized and universally available (§18.6). Coroutines are part of CPP20 (§18.6). The development of the template facility was influenced by a variety of vector, map, list, and sort templates devised by Andrew Koenig, Alex Stepanov, me, and others.” (TrCppBS 2022)

“The most important innovation in the 1998 standard library was the STL, a framework of algorithms and containers (Chapter 12, Chapter 13). It was the work of Alex Stepanov (with Dave Musser, Meng Lee, and others) based on more than a decade’s work on generic programming. The STL has been massively influential within the CPP community and beyond.” (TrCppBS 2022)

“CPP grew up in an environment with a multitude of established and experimental programming languages (e.g., Ada [Ichbiah,1979], Algol 68 [Woodward,1974], and ML [Paulson,1996]). At the time, I was comfortable in about 25 languages, and their influences on CPP are documented in [Stroustrup,1994] and [Stroustrup,2007]. However, the determining influences always came from the applications I encountered. It was my deliberate policy to have the evolution of CPP “problem driven” rather than imitative.” (TrCppBS 2022)

The ISO C++ Standards

ISO CPP Standards - CPP ISO Standards: 19.1.3 The ISO CPP Standards

“The explosive growth of CPP use caused some changes. Sometime during 1987, it became clear that formal standardization of CPP was inevitable and that we needed to lay the groundwork for a standardization effort [Stroustrup,1994]. The result was a conscious effort to maintain contact between implementers of CPP compilers and their major users. This was done through paper and electronic mail and through face-to-face meetings at CPP conferences and elsewhere.” (TrCppBS 2022)

“AT&T Bell Labs made a major contribution to CPP and its wider community by allowing me to share drafts of revised versions of the CPP reference manual with implementers and users. Because many of those people worked for companies that could be seen as competing with AT&T, the significance of this contribution should not be underestimated. A less enlightened company could have caused major problems of language fragmentation simply by doing nothing. As it happened, about a hundred individuals from dozens of organizations read and commented on what became the generally accepted reference manual and the base document for the ANSI CPP standardization effort. Their names can be found in The Annotated CPP Reference Manual (“the ARM”) [Ellis,1989]. The X3J16 committee of ANSI was convened in December 1989 at the initiative of Hewlett-Packard, DEC, and IBM with the support of AT&T. In June 1991, this ANSI (American national) standardization of CPP became part of an ISO (international) standardization effort for CPP. The ISO CPP committee is called WG21. From 1990 onward, these joint CPP standards committees have been the main forum for the evolution of CPP and the refinement of its definition. I served on these committees throughout. In particular, as the chairman of the working group for extensions (later called the evolution group) from 1990 to 2014, I was directly responsible for handling proposals for major changes to CPP and the addition of new language features. An initial draft standard for public review was produced in April 1995. The first ISO CPP standard (ISO/IEC 14882-1998) [CPP,1998] was ratified by a 22-0 national vote in 1998. A “bug fix release” of this standard was issued in 2003, so you sometimes hear people refer to CPP03, but that is essentially the same language and standard library as CPP98.” (TrCppBS 2022)

“CPP11, known for years as CPP0x, is the work of the members of WG21. The committee worked under increasingly onerous self-imposed processes and procedures. These processes probably led to a better (and more rigorous) specification, but they also limited innovation [Stroustrup,2007]. An initial draft standard for public review was produced in 2009. The second ISO CPP standard (ISO/IEC 14882-2011) [CPP,2011] was ratified by a 21-0 national vote in August 2011.” (TrCppBS 2022)

“One reason for the long gap between the two standards is that most members of the committee (including me) were under the mistaken impression that the ISO rules required a “waiting period” after a standard was issued before starting work on new features. Consequently, serious work on new language features did not start until 2002. Other reasons included the increased size of modern languages and their foundation libraries. In terms of pages of standards text, the language grew by about 30% and the standard library by about 100%. Much of the increase was due to more detailed specification, rather than new functionality. Also, the work on a new CPP standard obviously had to take great care not to compromise older code through incompatible changes. There are billions of lines of CPP code in use that the committee must not break. Stability over decades is an essential “feature.”” (TrCppBS 2022)

“CPP11 added massively to the standard library and pushed to complete the feature set needed for a programming style that is a synthesis of the “paradigms” and idioms that had proven successful with CPP98.” (TrCppBS 2022)

“The overall aims for the CPP11 effort were:” (TrCppBS 2022)

Make CPP a better language for systems programming and library building.
Make CPP easier to teach and learn.“

“The aims are documented and detailed in [Stroustrup,2007].” (TrCppBS 2022)

“A major effort was made to make concurrent systems programming type-safe and portable. This involved a memory model (§18.1) and support for lock-free programming, This was the work of Hans Boehm, Brian McKnight, and others in the concurrency working group. On top of that, we added the threads library.” (TrCppBS 2022)

“After CPP11, there was wide agreement that 13 years between standards were far too many. Herb Sutter proposed that the committee adopt a policy of shipping on time at fixed intervals, the “train model.” I argued strongly for a short interval between standards to minimize the chance of delays because someone insisted on extra time to allow inclusion of “just one more essential feature.” We agreed on an ambitious 3-year schedule with the idea that we should alternate between minor and major releases.” (TrCppBS 2022)

“CPP14 was deliberately a minor release aiming at “completing CPP11.” This reflects the reality that with a fixed release date, there will be features that we know we want, but can’t deliver on time. Also, once in widespread use, gaps in the feature set will inevitably be discovered.” (TrCppBS 2022)

“CPP17 was meant to be a major release. By “major,” I mean containing features that will change the way we think about the structure of our software and about how we design it. By this definition, CPP17 was at best a medium release. It included a lot of minor extensions, but the features that would have made dramatic changes (e.g., concepts, modules, and coroutines) were either not ready or became mired in controversy and lack of design direction. As a result, CPP17 includes a little bit for everyone, but nothing that would significantly change the life of a CPP programmer who had already absorbed the lessons of CPP11 and CPP14.” (TrCppBS 2022)

“CPP20 offers long-promised and much-needed major features, such as modules (§3.2.2), concepts (§8.2), coroutines (§18.6), ranges (§14.5), and many minor features. It is as major an upgrade to CPP as was CPP11. It became widely available in late 2021.” (TrCppBS 2022)

“The ISO CPP standards committee, SC22/WG21, now has about 350 members, out of which about 250 attended the last pre-pandemic face-to-face meeting in Prague where CPP20 was approved by a unanimous 79-0 that was later ratified by a national body vote of 22-0. Getting that degree of agreement among such a large and diverse group is hard work. Dangers include “Design by committee,” feature bloat, lack of consistent style, and short-sighted decisions. Making progress toward a simpler-to-use and more coherent language is very hard. The committee is aware of that and trying to counter it; see [Wong,2020]. Sometimes, we succeed but it is very hard to avoid complexity creeping in from “minor useful features,” fashion, and the desire of experts to serve rare special cases directly.” (TrCppBS 2022)

C++ Standards and Style

CPP Standards and CPP Style:

19.1.4 Standards and Style

A standard says what will work, and how. It does not say what constitutes good and effective use. There are significant differences between understanding the technical details of programming language features and using them effectively in combination with other features, libraries, and tools to produce better software. By “better” I mean “more maintainable, less error-prone, and faster.” We need to develop, popularize, and support coherent programming styles. Further, we must support the evolution of older code to these more modern, effective, and coherent styles.

With the growth of the language and its standard library, the problem of popularizing effective programming styles became critical. It is extremely difficult to make large groups of programmers depart from something that works for something better. There are still people who see CPP as a few minor additions to C and people who consider 1980s Object-Oriented programming styles based on massive class hierarchies the pinnacle of development. Many are still struggling to use modern CPP well in environments with lots of older CPP code. On the other hand, there are also many who enthusiastically overuse novel facilities. For example, some programmers are convinced that only code using massive amounts of template metaprogramming is true CPP.

What is Modern CPP? In 2015, I set out to answer this question by developing a set of coding guidelines supported by articulated rationales. I soon found that I was not alone in grappling with that problem, and together with people from many parts of the world, notably from Microsoft, Red Hat, and Facebook, started the “CPP Core Guidelines” project [Stroustrup,2015]. This is an ambitious project aiming at complete type-safety and complete resource-safety as a base for simpler, faster, safer, and more maintainable code [Stroustrup,2015b] [Stroustrup,2021]. In addition to specific coding rules with rationales, we back up the guidelines with static analysis tools and a tiny support library. I see something like that as necessary for moving the CPP community at large forward to benefit from the improvements in language features, libraries, and supporting tools.

19.1.5 CPP Use CPP is now a very widely used programming language. Its user population grew quickly from one in 1979 to about 400,000 in 1991; that is, the number of users doubled about every 7.5 months for more than a decade. Naturally, the growth rate slowed since that initial growth spurt, but my best estimate is that there were about 4.5 million CPP programmers in 2018 [Kazakova,2015] and maybe a million more today (2022). Much of that growth happened after 2005 when the exponential explosion of processor speed stopped so that language performance grew in importance. This growth was achieved without formal marketing or an organized user community [Stroustrup,2020].

CPP is primarily an industrial language; that is, it is more prominent in industry than in education or programming language research. It grew up in Bell Labs inspired by the varied and stringent needs of telecommunications and systems programming (including device drivers, networking, and embedded systems). From there, CPP use has spread into essentially every industry: microelectronics, Web applications and infrastructure, operating systems, financial, medical, automobile, aerospace, high-energy physics, biology, energy production, machine learning, video games, graphics, animation, virtual reality, and much more. It is primarily used where problems require CPP’s combination of the ability to use hardware effectively and to manage complexity. This seems to be a continuously expanding set of applications [Stroustrup,1993] [Stroustrup,2014] [Stroustrup,2020].

19.1.6 The CPP Model The CPP language can be summarized as a set of mutually supportive facilities:

A static type system with equal support for built-in types and user-defined types (Chapter 1, Chapter 5, Chapter 6)

Value and reference semantics (§1.7, §5.2, §6.2, Chapter 12, §15.2)

Systematic and general resource management (RAII) (§6.3)

Support for efficient object-oriented programming (§5.3, class.virtual, §5.5)

Support for flexible and efficient generic programming (Chapter 7, Chapter 18)

Support for compile-time programming (§1.6, Chapter 7, Chapter 8)

Direct use of machine and operating system resources (§1.4, Chapter 18)

Concurrency support through libraries (often implemented using intrinsics) (Chapter 18)

The standard-library components add further essential support for these high-level aims.

19.2 CPP Feature Evolution Here, I list the language features and standard-library components that have been added to CPP for the CPP11, CPP14, CPP17, and CPP20 standards.

19.2.1 CPP11 Language Features Looking at a list of language features can be quite bewildering. Remember that a language feature is not meant to be used in isolation. In particular, most features that are new in CPP11 make no sense in isolation from the framework provided by older features.

[1] Uniform and general initialization using {}-lists (§1.4.2, §5.2.3)

[2] Type deduction from initializer: auto (§1.4.2)

[3] Prevention of narrowing (§1.4.2)

[4] Generalized and guaranteed constant expressions: constexpr (§1.6)

[5] Range-for-statement (§1.7)

[6] Null pointer keyword: nullptr (§1.7.1)

[7] Scoped and strongly typed enums: enum class (§2.4)

[8] Compile-time assertions: static_assert (§4.5.2)

[9] Language mapping of {}-list to std::initializer_list (§5.2.3)

[10] Rvalue references, enabling move semantics (§6.2.2)

[11] Lambdas (§7.3.3)

[12] Variadic templates (§7.4.1)

[13] Type and template aliases (§7.4.2)

[14] Unicode characters

[15] long long integer type

[16] Alignment controls: alignas and alignof

[17] The ability to use the type of an expression as a type in a declaration: decltype

[18] Raw string literals (§10.4)

[19] Suffix return type syntax (§3.4.4)

[20] A syntax for attributes and two standard attributes: carries_dependency and noreturn

[21] A way of preventing exception propagation: the noexcept specifier (§4.4)

[22] Testing for the possibility of a throw in an expression: the noexcept operator

[23] C99 features: extended integral types (i.e., rules for optional longer integer types); concatenation of narrow/wide strings; __STDC_HOSTED__; _Pragma(X); vararg macros and empty macro arguments

[24] __func__ as the name of a string holding the name of the current function

[25] inline namespaces

[26] Delegating constructors

[27] In-class member initializers (§6.1.3)

[28] Control of defaults: default and delete (§6.1.1)

[29] Explicit conversion operators

[30] User-defined literals (§6.6)

[31] More explicit control of template instantiation: extern templates

[32] Default template arguments for function templates

[33] Inheriting constructors (§12.2.2)

[34] Override controls: override (§5.5) and final

[35] A simpler and more general SFINAE (Substitution Failure Is Not An Error) rule

[36] Memory model (§18.1)

[37] Thread-local storage: thread_local

For a more complete description of the changes to CPP98 in CPP11, see [Stroustrup,2013].

19.2.2 CPP14 Language Features [1] Function return-type deduction; (§3.4.3)

[2] Improved constexpr functions, e.g., for-loops allowed (§1.6)

[3] Variable templates (§7.4.1)

[4] Binary literals (§1.4)

[5] Digit separators (§1.4)

[6] Generic lambdas (§7.3.3.1)

[7] More general lambda capture

[8] deprecated attribute

[9] A few more minor extensions

19.2.3 CPP17 Language Features [1] Guaranteed copy elision (§6.2.2)

[2] Dynamic allocation of over-aligned types

[3] Stricter order of evaluation (§1.4.1)

[4] UTF-8 literals (u8)

[5] Hexadecimal floating-point literals (§11.6.1)

[6] Fold expressions (§8.4.1)

[7] Generic value template arguments (auto template parameters; §8.2.5)

[8] Class template argument type deduction (§7.2.3)

[9] Compile-time if (§7.4.3)

[10] Selection statements with initializers (§1.8)

[11] constexpr lambdas

[12] inline variables

[13] Structured bindings (§3.4.5)

[14] New standard attributes: fallthrough, nodiscard, and maybe_unused

[15] std::byte type (§16.7)

[16] Initialization of an enum by a value of its underlying type (§2.4)

[17] A few more minor extensions

19.2.4 CPP20 Language Features [1] Modules (§3.2.2)

[2] Concepts (§8.2)

[3] Coroutines (§18.6)

[4] Designated initializers (a slightly restricted version of a C99 feature)

[5] ⇔ (the “spaceship operator”) a three-way comparison (§6.5.1)

[6] [*this] to capture a current object by value (§7.3.3)

[7] Standard attributes no_unique_address, likely, and unlikely

[8] More facilities allowed in constexpr functions, including new, union, try-catch, dynamic_cast, and typeid.

[9] consteval functions guaranteeing compile-time evaluation (§1.6)

[10] constinit variables to guarantee static (not run-time) initialization (§1.6)

[11] using scoped enums (§2.4)

[12] A few more minor extensions

19.2.5 CPP11 Standard-Library Components The CPP11 additions to the standard library come in two forms: new components (such as the regular expression matching library) and improvements to CPP98 components (such as move constructors for containers).

[1] initializer_list constructors for containers (§5.2.3)

[2] Move semantics for containers (§6.2.2, §13.2)

[3] A singly-linked list: forward_list (§12.3)

[4] Hash containers: unordered_map, unordered_multimap, unordered_set, and unordered_multiset (§12.6, §12.8)

[5] Resource management pointers: unique_ptr, shared_ptr, and weak_ptr (§15.2.1)

[6] Concurrency support: thread (§18.2), mutexes and locks (§18.3), and condition variables (§18.4)

[7] Higher-level concurrency support: packaged_thread, future, promise, and async() (§18.5)

[8] tuples (§15.3.4)

[9] Regular expressions: regex (§10.4)

[10] Random numbers: distributions and engines (§17.5)

[11] Integer type names, such as int16_t, uint32_t, and int_fast64_t (§17.8)

[12] A fixed-sized contiguous sequence container: array (§15.3)

[13] Copying and rethrowing exceptions (§18.5.1)

[14] Error reporting using error codes: system_error

[15] emplace() operations for containers (§12.8)

[16] Wide use of constexpr functions

[17] Systematic use of noexcept functions

[18] Improved function adaptors: function and bind() (§16.3)

[19] string to numeric value conversions

[20] Scoped allocators

[21] Type traits, such as is_integral and is_base_of (§16.4.1)

[22] Time utilities: duration and time_point (§16.2.1)

[23] Compile-time rational arithmetic: ratio

[24] Abandoning a process: quick_exit (§16.8)

[25] More algorithms, such as move(), copy_if(), and is_sorted() (Chapter 13)

[26] Garbage collection API; later deprecated (§19.2.9)

[27] Low-level concurrency support: atomics (§18.3.2)

[28] A few more minor extensions

19.2.6 CPP14 Standard-Library Components [1] shared_mutex and shared_lock (§18.3)

[2] User-defined literals (§6.6)

[3] Tuple addressing by type (§15.3.4)

[4] Associative container heterogenous lookup

[5] A few more minor extensions

19.2.7 CPP17 Standard-Library Components [1] File system (§11.9)

[2] Parallel algorithms (§13.6, §17.3.1)

[3] Mathematical special functions (§17.2)

[4] string_view (§10.3)

[5] any (§15.4.3)

[6] variant (§15.4.1)

[7] optional (§15.4.2)

[8] A way of invoking anything that can be called for a given set of arguments: invoke()

[9] Elementary string conversions: to_chars() and from_chars()

[10] Polymorphic allocator (§12.7)

[11] scoped_lock (§18.3)

[12] A few more minor extensions

19.2.8 CPP20 Standard-Library Components [1] Ranges, views, and pipelines (§14.1)

[2] printf()-style formatting: format() and vformat() (§11.6.2)

[3] Calendars (§16.2.2) and time-zones (§16.2.3)

[4] span for read and write access to contiguous arrays (§15.2.2)

[5] source_location (§16.5)

[6] Mathematical constants, e.g., pi and ln10e (§17.9)

[7] Many extensions to atomics (§18.3.2)

[8] Ways of waiting for a numbet of threads: barrier and latch.

[9] Feature test macros

[10] bit_cast<> (§16.7)

[11] Bit operations (§16.7)

[12] More standard-library functions made constexpr

[13] Many uses of ⇔ in the standard library

[14] Many more minor extensions

19.2.9 Removed and Deprecated Features There are billions of lines of CPP “out there” and nobody knows exactly what features are in critical use. Consequently, the ISO committee removes older features only reluctantly and after years of warning. However, sometimes troublesome features are removed or deprecated.

By deprecating a feature, the standards committee expresses the wish that the feature will go away. However, the committee does not have the power to immediately remove a heavily used feature – however redundant or dangerous it may be. Thus, a deprecation is a strong hint to avoid the feature. It may disappear in the future. The list of deprecated features is in Appendix D of the standard [CPP,2020]. Compilers are likely to issue warnings for uses of deprecated features. However, deprecated features are part of the standard and history shows that they tend to remain supported “forever” for reasons of compatibility. Even features finally removed tend to live on in implementations because of user pressure on implementers.

Removed: Exception specifications: void f() throw(X,Y); // CPP98; now an error

Removed: The support facilities for exception specifications, unexpected_handler, set_unexpected(), get_unexpected(), and unexpected(). Instead, use noexcept (§4.2).

Removed: Trigraphs.

Removed: auto_ptr. Instead, use unique_ptr (§15.2.1).

Removed: The use of the storage specifier register.

Removed: The use of ++ on a bool.

Removed: The CPP98 export feature. It was complex and not shipped by the major vendors. Instead, export is used as a keyword for modules (§3.2.2).

Deprecated: Generation of copy operations for a class with a destructor (§6.2.1).

Removed: Assignment of a string literal to a char*. Instead use const c har* or auto.

Removed: Some CPP standard-library function objects and associated functions. Most relate to argument binding. Instead use lambdas and function (§16.3).

Deprecated: Comparisons of enum values with values from a different enum or a floating point value.

Deprecated: Comparisons between two arrays.

Deprecated: Comma operations in a subscript (e.g., [a,b]). To make room for allowing user defined operator[]() with multiple arguments.

Deprecated: Implicit capture of *this in lambda expressions. Instead, use [=,this] (§7.3.3).

Removed: The standard-library interface for garbage collectors. The CPP garbage collectors don’t use that interface.

Deprecated: strstream; instead, use spanstream (§11.7.4).

19.3 C/CPP Compatibility With minor exceptions, CPP is a superset of C (meaning C11; [C,2011]). Most differences stem from CPP’s greater emphasis on type checking. Well-written C programs tend to be CPP programs as well. For example, every example in K&R2 [Kernighan,1988] is CPP. A compiler can diagnose every difference between CPP and C. The C11/CPP20 incompatibilities are listed in Appendix C of the standard [CPP,2020].

19.3.1 C and CPP Are Siblings How can I call C and CPP siblings? Look at a simplified family tree:

Images Classic C has two main descendants: ISO C and ISO CPP. Over the years, these languages have evolved at different paces and in different directions. One result of this is that each language provides support for traditional C-style programming in slightly different ways. The resulting incompatibilities can make life miserable for people who use both C and CPP, for people who write in one language using libraries implemented in the other, and for implementers of libraries and tools for C and CPP.

A solid line means a massive inheritance of features, a dashed line a borrowing of major features, and a dotted line a borrowing of minor features. From this, ISO C and ISO CPP emerge as the two major descendants of K&R C [Kernighan,1978], and as siblings. Each carries with it the key aspects of Classic C, and neither is 100% compatible with Classic C. I picked the term “Classic C” from a sticker that used to be affixed to Dennis Ritchie’s terminal. It is K&R C plus enumerations and struct assignment. BCPL is defined by [Richards,1980] and C89 by [C1990].

There was a CPP03, which I didn’t list because it was a bug-fix release. Similarly, C17 is not listed because it is a bug-fix release to C11.

Note that differences between C and CPP are not necessarily the result of changes to C made in CPP. In several cases, the incompatibilities arise from features adopted incompatibly into C long after they were common in CPP. Examples are the ability to assign a T* to a void* and the linkage of global consts [Stroustrup,2002]. Sometimes, a feature was even incompatibly adopted into C after it was part of the ISO CPP standard, such as details of the meaning of inline.

19.3.2 Compatibility Problems There are many minor incompatibilities between C and CPP. All can cause problems for a programmer but in the context of CPP, all can be coped with. If nothing else, C code fragments can be compiled as C and linked to using the extern “C” mechanism.

The major problems for converting a C program to CPP are likely to be:

Suboptimal design and programming style.

A void* implicitly converted to a T* (that is, converted without a cast).

CPP keywords, such as class and private, used as identifiers in C code.

Incompatible linkage of code fragments compiled as C and fragments compiled as CPP.

19.3.2.1 Style Problems Naturally, a C program is written in a C style, such as the style used in K&R [Kernighan,1988]. This implies widespread use of pointers and arrays, and probably many macros. These facilities are hard to use reliably in a large program. Resource management and error handling are often ad hoc (rather than language and tool supported) and often incompletely documented and adhered to. A simple line-for-line conversion of a C program into a CPP program yields a program that is often a bit better checked. In fact, I have never converted a C program into CPP without finding some bugs. However, the fundamental structure is unchanged, and so are the fundamental sources of errors. If you had incomplete error handling, resource leaks, or buffer overflows in the original C program, they will still be there in the CPP version. To obtain major benefits, you must make changes to the fundamental structure of the code:

[1] Don’t think of CPP as C with a few features added. CPP can be used that way, but only suboptimally. To get really major advantages from CPP as compared to C, you need to apply different design and implementation styles.

[2] Use the CPP standard library as a teacher of new techniques and programming styles. Note the difference from the C standard library (e.g., = rather than strcpy() for copying).

[3] Macro substitution is almost never necessary in CPP. Use const (§1.6), constexpr (§1.6), enum or enum class (§2.4) to define manifest constants, constexpr (§1.6), consteval (§1.6), and inline (§5.2.1) to avoid function-calling overhead, templates (Chapter 7) to specify families of functions and types, and namespaces (§3.3) to avoid name clashes.

[4] Don’t declare a variable before you need it, and initialize it immediately. A declaration can occur anywhere a statement can (§1.8), such as in for-statement initializers and in conditions (§1.8).

[5] Don’t use malloc(). The new operator (§5.2.2) does the same job better, and instead of realloc(), try a vector (§6.3, §12.2). Don’t just replace malloc() and free() with “naked” new and delete (§5.2.2).

[6] Avoid void*, unions, and casts, except deep within the implementation of some function or class. Their use limits the support you can get from the type system and can harm performance. In most cases, a cast is an indication of a design error.

[7] If you must use an explicit type conversion, use an appropriate named cast (e.g., static_cast; §5.2.3) for a more precise statement of what you are trying to do.

[8] Minimize the use of arrays and C-style strings. CPP standard-library strings (§10.2), arrays (§15.3.1), and vectors (§12.2) can often be used to write simpler and more maintainable code compared to the traditional C style. In general, try not to build yourself what has already been provided by the standard library.

[9] Avoid pointer arithmetic except in very specialized code (such as a memory manager).

[10] Pass contiguous sequences (e.g., arrays) as spans (§15.2.2). It’s a good way to avoid range errors (“buffer overruns”) without added tests.

[11] For simple array traversal, use range-for (§1.7). It’s easier to write, as fast as, and safer than a traditional C loop.

[12] Use nullptr (§1.7.1) rather than 0 or NULL.

[13] Do not assume that something laboriously written in C style (avoiding CPP features such as classes, templates, and exceptions) is more efficient than a shorter alternative (e.g., using standard-library facilities). Often (but of course not always), the opposite is true.

19.3.2.2 void* In C, a void* may be used as the right-hand operand of an assignment to or initialization of a variable of any pointer type; in CPP it may not. For example:

Click here to view code image

void f(int n) {

       int* p = malloc(n*sizeof(int));  /* not CPP; in CPP, allocate using “new”*/
       // ...

} This is probably the single most difficult incompatibility to deal with. Note that the implicit conversion of a void* to a different pointer type is not in general harmless:

Click here to view code image

char ch; void* pv = &ch; int* pi = pv; // not CPP

pi = 666; // overwrite ch and other bytes near ch

In both languages, cast the result of malloc() to the right type. If you use only CPP, avoid malloc().

19.3.2.3 Linkage C and CPP can be (and often are) implemented to use different linkage conventions. The most basic reason for that is CPP’s greater emphasis on type checking. A practical reason is that CPP supports overloading, so there can be two global functions called open(). This has to be reflected in the way the linker works.

To give a CPP function C linkage (so that it can be called from a C program fragment) or to allow a C function to be called from a CPP program fragment, declare it extern “C”. For example:

Click here to view code image

extern “C” double sqrt(double); Now sqrt(double) can be called from a C or a CPP code fragment. The definition of sqrt(double) can also be compiled as a C function or as a CPP function.

Only one function of a given name in a scope can have C linkage (because C doesn’t allow function overloading). A linkage specification does not affect type checking, so the CPP rules for function calls and argument checking still apply to a function declared extern “C”.

” (TrCppBS 2022)

C++Bibliography

CPP Bibliography

19.4 Bibliography

Boost – The Boost Libraries - free peer-reviewed portable CPP source libraries. https://boost.org.

C,1990 – X3 Secretariat - Standard – The C Language. X3J11/90-013. ISO Standard ISO/IEC 9899-1990. Computer and Business Equipment Manufacturers Association. Washington, DC.

C,1999 – ISO/IEC 9899. Standard – The C Language. X3J11/90-013-1999.

C,2011 – ISO/IEC 9899. Standard – The C Language. X3J11/90-013-2011.

CPP,1998 – ISO/IEC JTC1/SC22/WG21 (editor - Andrew Koenig): International Standard – The CPP Language. ISO/IEC 14882 1998.

CPP,2004 – ISO/IEC JTC1/SC22/WG21 (editor: Lois Goldthwaite): Technical Report on CPP Performance. ISO/IEC TR 18015 2004(E) ISO/IEC 29124 2010.

CPP,2011 – ISO/IEC JTC1/SC22/WG21 (editor: Pete Becker): International Standard – The CPP Language. ISO/IEC 14882 2011.

CPP,2014 – ISO/IEC JTC1/SC22/WG21 (editor: Stefanus Du Toit): International Standard – The CPP Language. ISO/IEC 14882 2014.

CPP,2017 – ISO/IEC JTC1/SC22/WG21 (editor: Richard Smith): International Standard – The CPP Language. ISO/IEC 14882 2017.

CPP,2020 – ISO/IEC JTC1/SC22/WG21 (editor: Richard Smith): International Standard – The CPP Language. ISO/IEC 14882 2020.

Cppcoro – CppCoro – A coroutine library for CPP. https://github.com/lewissbaker/cppcoro.

Cppreference – CPP Online source for CPP language and CPP standard library facilities. https://cppreference.com.

Cox,2007 – Russ Cox, CPPP Regular Expression Matching Can Be Simple And Fast. January 2007. https://swtch.com/~rsc/regexp/regexp1.html.

Dahl,1970 – O-J. Dahl, B. Myrhaug, and K. Nygaard: SIMULA Common Base Language. Norwegian Computing Center S-22. Oslo, Norway. 1970.

Dechev,2010 – D. Dechev, P. Pirkelbauer, and B. Stroustrup: CPP Understanding and Effectively Preventing the ABA Problem in Descriptor-based Lock-free Designs. 13th IEEE Computer Society ISORC 2010 Symposium. May 2010.

DosReis,2006 – Gabriel Dos Reis and Bjarne Stroustrup: CPP Specifying CPP Concepts. POPL06. January 2006.

Ellis,1989 – Margaret A. Ellis and Bjarne Stroustrup: The Annotated CPP Reference Manual. pAddison-Wesley. Reading, Massachusetts. 1990. ISBN 0-201-51459-1.

Garcia,2015 – J. Daniel Garcia and B. Stroustrup: CPP Improving performance and maintainability through refactoring in CPP11. Isocpp.org. August 2015. http://https://stroustrup.com/improving_garcia_stroustrup_2015.pdf.

Friedl,1997 – Jeffrey E. F. Friedl: O'Reilly>Mastering Regular Expressions. O’Reilly Media. Sebastopol, California. 1997. ISBN 978-1565922570.

Gregor,2006 – Douglas Gregor et al.: CPP Concepts - Linguistic Support for Generic Programming in CPP. OOPSLA’06.

Ichbiah,1979 – Jean D. Ichbiah et al.: Rationale for the Design of the ADA Programming Language. SIGPLAN Notices. Vol. 14, No. 6. June 1979.

Kazakova,2015 – Anastasia Kazakova: Infographic: C/CPP facts. https://blog.jetbrains.com/clion/2015/07/infographics-cpp-facts-before-clion - JetBrains CLion, July 2015.

Kernighan,1978 – Brian W. Kernighan and Dennis M. Ritchie - The C Programming Language. Prentice Hall. Englewood Cliffs, New Jersey. 1978.

Kernighan,1988 – Brian W. Kernighan and Dennis M. Ritchie - The C Programming Language, Second Edition. Prentice-Hall. Englewood Cliffs, New Jersey. 1988. ISBN 0-13-110362-8.

Knuth,1968 – Donald E. Knuth - The Art of Computer Programming. Addison-Wesley. Reading, Massachusetts. 1968.

Koenig,1990 – A. R. Koenig and B. Stroustrup: Exception Handling for CPP (revised). Proc USENIX CPP Conference. April 1990.

Maddock,2009 – John Maddock: Boost.Regex. https://boost.org. 2009. 2017.

Orwell,1949 – George Orwell: 1984. Secker and Warburg. London. 1949.

Paulson,1996 – Larry C. Paulson: ML for the Working Programmer. Cambridge University Press. Cambridge. 1996. ISBN 978-0521565431.

Richards,1980 – Martin Richards and Colin Whitby-Strevens: BCPL – The Language and Its Compiler. Cambridge University Press. Cambridge. 1980. ISBN 0-521-21965-5.

Stepanov,1994 – Alexander Stepanov and Meng Lee: The Standard Template Library. HP Labs Technical Report HPL-94-34 (R. 1). 1994.

Stepanov,2009 – Alexander Stepanov and Paul McJones: Elements of Programming. Addison-Wesley. Boston, Massachusetts. 2009. ISBN 978-0-321-63537-2.

Stroustrup,1979 – Personal lab notes.

Stroustrup,1982 – B. Stroustrup: Classes - An Abstract Data Type Facility for the C Language. Sigplan Notices. January 1982. The first public description of “C with Classes.”

Stroustrup,1984 – B. Stroustrup: Operator Overloading in CPP. Proc. IFIP WG2.4 Conference on System Implementation Languages: Experience & Assessment. September 1984.

Stroustrup,1985 – B. Stroustrup: An Extensible I/O Facility for CPP. Proc. Summer 1985 USENIX Conference.

Stroustrup,1986 – B. Stroustrup: The CPP Programming Language. Addison-Wesley. Reading, Massachusetts. 1986. ISBN 0-201-12078-X.

Stroustrup,1987 – B. Stroustrup: Multiple Inheritance for CPP. Proc. EUUG Spring Conference. May 1987.

Stroustrup,1987b – B. Stroustrup and J. Shopiro: A Set of C Classes for Co-Routine Style Programming. Proc. USENIX CPP Conference. Santa Fe, New Mexico. November 1987.

Stroustrup,1988 – B. Stroustrup: Parameterized Types for CPP. Proc. USENIX CPP Conference, Denver, Colorado. 1988.

Stroustrup,1991 – B. Stroustrup: The CPP Programming Language (Second Edition). Addison-Wesley. Reading, Massachusetts. 1991. ISBN 0-201-53992-6.

Stroustrup,1993 – B. Stroustrup: A History of CPP: 1979–1991. Proc. ACM History of Programming Languages Conference (HOPL-2). ACM Sigplan Notices. Vol 28, No 3. 1993.

Stroustrup,1994 – B. Stroustrup: The Design and Evolution of CPP. Addison-Wesley. Reading, Massachusetts. 1994. ISBN 0-201-54330-3.

Stroustrup,1997 – B. Stroustrup: The CPP Programming Language, Third Edition. Addison-Wesley. Reading, Massachusetts. 1997. ISBN 0-201-88954-4. Hardcover (“Special”) Edition. 2000. ISBN 0-201-70073-5.

Stroustrup,2002 – B. Stroustrup: C and CPP: Siblings, C and CPP: A Case for Compatibility, and C and CPP: Case Studies in Compatibility. The C/CPP Users Journal. July-September 2002. https://stroustrup.com/papers.html.

Stroustrup,2007 – B. Stroustrup: Evolving a language in and for the real world: CPP 1991-2006. ACM HOPL-III. June 2007.

Stroustrup,2009 – B. Stroustrup: Programming – Principles and Practice Using CPP. Addison-Wesley. Boston, Massachusetts. 2009. ISBN 0-321-54372-6.

Stroustrup,2010 – B. Stroustrup: “New” Value Terminology. https://stroustrup.com/terminology.pdf. April 2010.

Stroustrup,2012a – B. Stroustrup and A. Sutton: A Concept Design for the STL. WG21 Technical Report N3351==12-0041. January 2012.

Stroustrup,2012b – B. Stroustrup: Software Development for Infrastructure. Computer. January 2012. doi:10.1109/MC.2011.353.

Stroustrup,2013 – B. Stroustrup: The CPP Programming Language (Fourth Edition). Addison-Wesley. Boston, Massachusetts. 2013. ISBN 0-321-56384-0.

Stroustrup,2014 – B. Stroustrup: CPP Applications. https://stroustrup.com/applications.html.

Stroustrup,2015 – B. Stroustrup and H. Sutter: CPP Core Guidelines. https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md.

Stroustrup,2015b – B. Stroustrup, H. Sutter, and G. Dos Reis: A brief introduction to CPP’s model for type- and resource-safety. Isocpp.org. October 2015. Revised December 2015. http://https://stroustrup.com/resource-model.pdf.