Misplaced Pages

#615384

97-522: The report was first circulated in draft form in 2005 as Draft Technical Report on C++ Library Extensions , then published in 2007 as an ISO/IEC standard as ISO/IEC TR 19768:2007 . Compilers did not need to include the TR1 components in order to conform to the C++ standard, because TR1 proposals were not part of the standard itself, only a set of possible additions that were still to be ratified. However, most of TR1

194-533: A basic block , to whole procedures, or even the whole program. There is a trade-off between the granularity of the optimizations and the cost of compilation. For example, peephole optimizations are fast to perform during compilation but only affect a small local fragment of the code, and can be performed independently of the context in which the code fragment appears. In contrast, interprocedural optimization requires more compilation time and memory space, but enable optimizations that are only possible by considering

291-412: A concrete syntax tree (CST, parse tree) and then transforming it into an abstract syntax tree (AST, syntax tree). In some cases additional phases are used, notably line reconstruction and preprocessing, but these are rare. The main phases of the front end include the following: The middle end, also known as optimizer, performs optimizations on the intermediate representation in order to improve

388-422: A PDP-7 in B. Unics eventually became spelled Unix. Bell Labs started the development and expansion of C based on B and BCPL. The BCPL compiler had been transported to Multics by Bell Labs and BCPL was a preferred language at Bell Labs. Initially, a front-end program to Bell Labs' B compiler was used while a C compiler was developed. In 1971, a new PDP-11 provided the resource to define extensions to B and rewrite

485-437: A Production Quality Compiler (PQC) from formal definitions of source language and the target. PQCC tried to extend the term compiler-compiler beyond the traditional meaning as a parser generator (e.g., Yacc ) without much success. PQCC might more properly be referred to as a compiler generator. PQCC research into code generation process sought to build a truly automatic compiler-writing system. The effort discovered and designed

582-452: A certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness . In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and K&R sections to prevent

679-405: A compiler up into small programs is a technique used by researchers interested in producing provably correct compilers. Proving the correctness of a set of small programs often requires less effort than proving the correctness of a larger, single, equivalent program. Regardless of the exact number of phases in the compiler design, the phases can be assigned to one of three stages. The stages include

776-432: A component of an IDE (VADS, Eclipse, Ada Pro). The interrelationship and interdependence of technologies grew. The advent of web services promoted growth of web languages and scripting languages. Scripts trace back to the early days of Command Line Interfaces (CLI) where the user could enter commands to be executed by the system. User Shell concepts developed with languages to write shell programs. Early Windows designs offered

873-628: A front end, a middle end, and a back end. This front/middle/back-end approach makes it possible to combine front ends for different languages with back ends for different CPUs while sharing the optimizations of the middle end. Practical examples of this approach are the GNU Compiler Collection , Clang ( LLVM -based C/C++ compiler), and the Amsterdam Compiler Kit , which have multiple front-ends, shared optimizations and multiple back-ends. The front end analyzes

970-527: A grammar for the language, though in more complex cases these require manual modification. The lexical grammar and phrase grammar are usually context-free grammars , which simplifies analysis significantly, with context-sensitivity handled at the semantic analysis phase. The semantic analysis phase is generally more complex and written by hand, but can be partially or fully automated using attribute grammars . These phases themselves can be further broken down: lexing as scanning and evaluating, and parsing as building

1067-483: A number of Technical Specifications. Some of the proposals listed above are already included in the C++ standard or in draft versions of the Technical Specifications. Compilers In computing , a compiler is a computer program that translates computer code written in one programming language (the source language) into another language (the target language). The name "compiler"

SECTION 10

#1732783999616

1164-432: A result, compilers were split up into smaller programs which each made a pass over the source (or some representation of it) performing some of the required analysis and translations. The ability to compile in a single pass has classically been seen as a benefit because it simplifies the job of writing a compiler and one-pass compilers generally perform compilations faster than multi-pass compilers . Thus, partly driven by

1261-590: A semicolon; as a side effect of the evaluation, functions may be called and variables assigned new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. Structured programming is supported by if ... [ else ] conditional execution and by do ... while , while , and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted. break and continue can be used within

1358-431: A simple batch programming capability. The conventional transformation of these language used an interpreter. While not widely used, Bash and Batch compilers have been written. More recently sophisticated interpreted languages became part of the developers tool kit. Modern scripting languages include PHP, Python, Ruby and Lua. (Lua is widely used in game development.) All of these have interpreter and compiler support. "When

1455-423: A warning message if a local function was called with the wrong number of arguments, or if different calls to an external function used different numbers or types of arguments. Separate tools such as Unix's lint utility were developed that (among other things) could check for consistency of function use across multiple source files. In the years following the publication of K&R C, several features were added to

1552-612: A wide variety of mainframe computers , minicomputers , and microcomputers , including the IBM PC , as its popularity began to increase significantly. In 1983 the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to

1649-492: Is Open64 , which is used by many organizations for research and commercial purposes. Due to the extra time and space needed for compiler analysis and optimizations, some compilers skip them by default. Users have to use compilation options to explicitly tell the compiler which optimizations should be enabled. The back end is responsible for the CPU architecture specific optimizations and for code generation . The main phases of

1746-467: Is also allowed. This is a generalized version of the standard std::bind1st and std::bind2nd bind functions. The feature is based on Boost Bind library. Function return types ( result_of ) – determines the type of a call expression. Member functions ( mem_fn ) – enhancement to the standard std::mem_fun and std::mem_fun_ref . Allows pointers to member functions to be treated as function objects. Based on Boost Mem Fn library. There

1843-613: Is also commercial support, for example, AdaCore, was founded in 1994 to provide commercial software solutions for Ada. GNAT Pro includes the GNU GCC based GNAT with a tool suite to provide an integrated development environment . High-level languages continued to drive compiler research and development. Focus areas included optimization and automatic code generation. Trends in programming languages and development environments influenced compiler technology. More compilers became included in language distributions (PERL, Java Development Kit) and as

1940-498: Is an imperative , procedural language in the ALGOL tradition. It has a static type system . In C, all executable code is contained within subroutines (also called "functions", though not in the sense of functional programming ). Function parameters are passed by value, although arrays are passed as pointers , i.e. the address of the first item in the array. Pass-by-reference is simulated in C by explicitly passing pointers to

2037-456: Is an informal name for the current major C language standard revision. It was informally known as "C2X" through most of its development. C23 was published in October 2024 as ISO/IEC 9899:2024. The standard macro __STDC_VERSION__ is defined as 202311L to indicate that C23 support is available. C2Y is an informal name for the next major C language standard revision, after C23 (C2X), that

SECTION 20

#1732783999616

2134-456: Is commonly used on computer architectures that range from the largest supercomputers to the smallest microcontrollers and embedded systems . A successor to the programming language B , C was originally developed at Bell Labs by Ritchie between 1972 and 1973 to construct utilities running on Unix . It was applied to re-implementing the kernel of the Unix operating system. During the 1980s, C gradually gained popularity. It has become one of

2231-504: Is defined as 201112L to indicate that C11 support is available. C17 is an informal name for ISO/IEC 9899:2018, a standard for the C programming language published in June 2018. It introduces no new language features, only technical corrections, and clarifications to defects in C11. The standard macro __STDC_VERSION__ is defined as 201710L to indicate that C17 support is available. C23

2328-446: Is favored due to its modularity and separation of concerns . Most commonly, the frontend is broken into three phases: lexical analysis (also known as lexing or scanning), syntax analysis (also known as scanning or parsing), and semantic analysis . Lexing and parsing comprise the syntactic analysis (word syntax and phrase syntax, respectively), and in simple cases, these modules (the lexer and parser) can be automatically generated from

2425-524: Is for the most part backward compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available. GCC , Solaris Studio , and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++ , however, implements

2522-469: Is hoped to be released later in the 2020s decade, hence the '2' in "C2Y". An early working draft of C2Y was released in February 2024 as N3220 by the working group ISO/IEC JTC1/SC22 /WG14. Historically, embedded C programming requires non-standard extensions to the C language to support exotic features such as fixed-point arithmetic , multiple distinct memory banks , and basic I/O operations. In 2008,

2619-478: Is now <type_traits> header file that contains many useful trait meta-templates, such as is_pod , has_virtual_destructor , remove_extent , etc. It facilitates metaprogramming by enabling queries on and transformation between different types . The proposal is based on Boost Type Traits library. Some features of TR1, such as the mathematical special functions and certain C99 additions, are not included in

2716-622: Is now also referred to as C78 . The second edition of the book covers the later ANSI C standard, described below. K&R introduced several language features: Even after the publication of the 1989 ANSI standard, for many years K&R C was still considered the " lowest common denominator " to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C code can be legal Standard C as well. In early versions of C, only functions that return types other than int must be declared if used before

2813-417: Is primarily used for programs that translate source code from a high-level programming language to a low-level programming language (e.g. assembly language , object code , or machine code ) to create an executable program. There are many different types of compilers which produce output in different useful forms. A cross-compiler produces code for a different CPU or operating system than

2910-420: Is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language. ANSI, like other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained by the working group ISO/IEC JTC1/SC22 /WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication. One of

3007-426: Is used (for a constant reference cref is used). Wrapper references are useful above all for template functions, when argument deduction would not deduce a reference (e.g. when forwarding arguments): Smart pointers – adds several classes that simplify object lifetime management in complex cases. Three main classes are added: The proposal is based on Boost Smart Pointer library. These four modules are added to

C++ Technical Report 1 - Misplaced Pages Continue

3104-438: The <functional> header file: Polymorphic function wrapper ( function ) – can store any callable function (function pointers, member function pointers, and function objects) that uses a specified function call signature. The type does not depend on the kind of the callable used. Based on Boost.Function Function object binders ( bind ) – can bind any parameter parameters to function objects. Function composition

3201-597: The C99 version of the C standard (not all parts of C99 are included in TR1). In 2005, a request for proposals for a TR2 was made with a special interest in Unicode, XML/HTML, Networking and usability for novice programmers. TR2 call for proposals . Some of the proposals included: After the call was issued for proposals for TR2, ISO procedures were changed, so there will not be a TR2. Instead, enhancements to C++ will be published in

3298-597: The IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Language C". This version of the language is often referred to as ANSI C , Standard C, or sometimes C89. In 1990 the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) as ISO/IEC 9899:1990, which

3395-590: The International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). C is an imperative procedural language, supporting structured programming , lexical variable scope , and recursion , with a static type system . It was designed to be compiled to provide low-level access to memory and language constructs that map efficiently to machine instructions , all with minimal runtime support . Despite its low-level capabilities,

3492-599: The (since 1995, object-oriented) programming language Ada . The Ada STONEMAN document formalized the program support environment (APSE) along with the kernel (KAPSE) and minimal (MAPSE). An Ada interpreter NYU/ED supported development and standardization efforts with the American National Standards Institute (ANSI) and the International Standards Organization (ISO). Initial Ada compiler development by

3589-483: The C Standards Committee published a technical report extending the C language to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as fixed-point arithmetic, named address spaces, and basic I/O hardware addressing. C has a formal grammar specified by the C standard. Line endings are generally not significant in C; however, line boundaries do have significance during

3686-548: The C89 standard and those parts of C99 that are required for compatibility with C++11 . In addition, the C99 standard requires support for identifiers using Unicode in the form of escaped characters (e.g. \u0040 or \U0001f431 ) and suggests support for raw Unicode names. Work began in 2007 on another revision of the C standard, informally called "C1X" until its official publication of ISO/IEC 9899:2011 on December 8, 2011. The C standards committee adopted guidelines to limit

3783-587: The Early PL/I (EPL) compiler by Doug McIlory and Bob Morris from Bell Labs. EPL supported the project until a boot-strapping compiler for the full PL/I could be developed. Bell Labs left the Multics project in 1969, and developed a system programming language B based on BCPL concepts, written by Dennis Ritchie and Ken Thompson . Ritchie created a boot-strapping compiler for B and wrote Unics (Uniplexed Information and Computing Service) operating system for

3880-528: The Sun 3/60 Solaris targeted to Motorola 68020 in an Army CECOM evaluation. There were soon many Ada compilers available that passed the Ada Validation tests. The Free Software Foundation GNU project developed the GNU Compiler Collection (GCC) which provides a core capability to support multiple languages and targets. The Ada version GNAT is one of the most widely used Ada compilers. GNAT is free but there

3977-670: The U.S. Military Services included the compilers in a complete integrated design environment along the lines of the STONEMAN document. Army and Navy worked on the Ada Language System (ALS) project targeted to DEC/VAX architecture while the Air Force started on the Ada Integrated Environment (AIE) targeted to IBM 370 series. While the projects did not provide the desired results, they did contribute to

C++ Technical Report 1 - Misplaced Pages Continue

4074-471: The University of Cambridge was originally developed as a compiler writing tool. Several compilers have been implemented, Richards' book provides insights to the language and its compiler. BCPL was not only an influential systems programming language that is still used in research but also provided a basis for the design of B and C languages. BLISS (Basic Language for Implementation of System Software)

4171-565: The Visual C++ implementation of TR1. The Mathematical special functions library was not standardized in C++11. These functions will likely be of principal interest to programmers in the engineering and scientific disciplines. The following table shows all 23 special functions described in TR1. Cylindrical Bessel functions of the second kind Spherical Bessel functions of the second kind Each function has two additional variants. Appending

4268-438: The adoption of new features that had not been tested by existing implementations. The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It also makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__

4365-428: The aims of the C standardization process was to produce a superset of K&R C, incorporating many of the subsequently introduced unofficial features. The standards committee also included several additional features such as function prototypes (borrowed from C++), void pointers, support for international character sets and locales , and preprocessor enhancements. Although the syntax for parameter declarations

4462-587: The back end include the following: C (programming language)#C99 This is an accepted version of this page C ( pronounced / ˈ s iː / – like the letter c ) is a general-purpose programming language . It was created in the 1970s by Dennis Ritchie and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted CPUs. It has found lasting use in operating systems code (especially in kernels ), device drivers , and protocol stacks , but its use in application software has been decreasing. C

4559-416: The basis for several implementations of C on new platforms. In 1978 Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language . Known as K&R from the initials of its authors, the book served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as " K&R C ". As this was released in 1978, it

4656-435: The basis of digital modern computing development during World War II. Primitive binary languages evolved because digital devices only understand ones and zeros and the circuit patterns in the underlying machine architecture. In the late 1940s, assembly languages were created to offer a more workable abstraction of the computer architectures. Limited memory capacity of early computers led to substantial technical challenges when

4753-433: The behavior of multiple functions simultaneously. Interprocedural analysis and optimizations are common in modern commercial compilers from HP , IBM , SGI , Intel , Microsoft , and Sun Microsystems . The free software GCC was criticized for a long time for lacking powerful interprocedural optimizations, but it is changing in this respect. Another open source compiler with full analysis and optimization infrastructure

4850-540: The compiler. By 1973 the design of C language was essentially complete and the Unix kernel for a PDP-11 was rewritten in C. Steve Johnson started development of Portable C Compiler (PCC) to support retargeting of C compilers to new machines. Object-oriented programming (OOP) offered some interesting possibilities for application development and maintenance. OOP concepts go further back but were part of LISP and Simula language science. Bell Labs became interested in OOP with

4947-407: The development of C++ . C++ was first used in 1980 for systems programming. The initial design leveraged C language systems programming capabilities with Simula concepts. Object-oriented facilities were added in 1983. The Cfront program implemented a C++ front-end for C84 language compiler. In subsequent years several C++ compilers were developed as C++ popularity grew. In many application domains,

SECTION 50

#1732783999616

5044-551: The development of compiler technology: Early operating systems and software were written in assembly language. In the 1960s and early 1970s, the use of high-level languages for system programming was still controversial due to resource limitations. However, several research and industry efforts began the shift toward high-level systems programming languages, for example, BCPL , BLISS , B , and C . BCPL (Basic Combined Programming Language) designed in 1966 by Martin Richards at

5141-424: The development of high-level languages followed naturally from the capabilities offered by digital computers. High-level languages are formal languages that are strictly defined by their syntax and semantics which form the high-level language architecture. Elements of these formal languages include: The sentences in a language may be defined by a set of rules called a grammar. Backus–Naur form (BNF) describes

5238-424: The early days, the approach taken to compiler design was directly affected by the complexity of the computer language to be processed, the experience of the person(s) designing it, and the resources available. Resource limitations led to the need to pass through the source code more than once. A compiler for a relatively simple language written by one person might be a single, monolithic piece of software. However, as

5335-650: The features of the more-powerful PDP-11. A significant addition was a character data type. He called this New B (NB). Thompson started to use NB to write the Unix kernel, and his requirements shaped the direction of the language development. Through to 1972, richer types were added to the NB language: NB had arrays of int and char . Pointers, the ability to generate pointers to other types, arrays of all types, and types to be returned from functions were all also added. Arrays within expressions became pointers. A new compiler

5432-491: The field of compiling began in the late 50s, its focus was limited to the translation of high-level language programs into machine code ... The compiler field is increasingly intertwined with other disciplines including computer architecture, programming languages, formal methods, software engineering, and computer security." The "Compiler Research: The Next 50 Years" article noted the importance of object-oriented languages and Java. Security and parallel computing were cited among

5529-464: The first (algorithmic) programming language for computers called Plankalkül ("Plan Calculus"). Zuse also envisioned a Planfertigungsgerät ("Plan assembly device") to automatically translate the mathematical formulation of a program into machine-readable punched film stock . While no actual implementation occurred until the 1970s, it presented concepts later seen in APL designed by Ken Iverson in

5626-423: The first compilers were designed. Therefore, the compilation process needed to be divided into several small programs. The front end programs produce the analysis products used by the back end programs to generate target code. As computer technology provided more resources, compiler designs could align better with the compilation process. It is usually more productive for a programmer to use a high-level language, so

5723-559: The first pass needs to gather information about declarations appearing after statements that they affect, with the actual translation happening during a subsequent pass. The disadvantage of compiling in a single pass is that it is not possible to perform many of the sophisticated optimizations needed to generate high quality code. It can be difficult to count exactly how many passes an optimizing compiler makes. For instance, different phases of optimization may analyse one expression many times but only analyse another expression once. Splitting

5820-423: The following components: Reference wrapper – enables passing references , rather than copies, into algorithms or function objects. The feature was based on Boost.Ref. A wrapper reference is obtained from an instance of the template class reference_wrapper . Wrapper references are similar to normal references (‘&’) of the C++ language. To obtain a wrapper reference from any object the template class ref

5917-933: The form of expressions without a change of language; and compiler-compilers , compilers that produce compilers (or parts of them), often in a generic and reusable way so as to be able to produce many differing compilers. A compiler is likely to perform some or all of the following operations, often called phases: preprocessing , lexical analysis , parsing , semantic analysis ( syntax-directed translation ), conversion of input programs to an intermediate representation , code optimization and machine specific code generation . Compilers generally implement these phases as modular components, promoting efficient design and correctness of transformations of source input to target output. Program faults caused by incorrect compiler behavior can be very difficult to track down and work around; therefore, compiler implementers invest significant effort to ensure compiler correctness . Compilers are not

SECTION 60

#1732783999616

6014-477: The function definition; functions used without prior declaration were presumed to return type int . For example: The int type specifiers which are commented out could be omitted in K&;R C, but are required in later standards. Since K&R function declarations did not include any information about function arguments, function parameter type checks were not performed, although some compilers would issue

6111-454: The future research targets. A compiler implements a formal transformation from a high-level source program to a low-level target program. Compiler design can define an end-to-end solution or tackle a defined subset that interfaces with other compilation tools e.g. preprocessors, assemblers, linkers. Design requirements include rigorously defined interfaces both internally between compiler components and externally between supporting toolsets. In

6208-421: The idea of using a higher-level language quickly caught on. Because of the expanding functionality supported by newer programming languages and the increasing complexity of computer architectures, compilers became more complex. DARPA (Defense Advanced Research Projects Agency) sponsored a compiler project with Wulf's CMU research team in 1970. The Production Quality Compiler-Compiler PQCC design would produce

6305-452: The language was designed to encourage cross-platform programming. A standards -compliant C program written with portability in mind can be compiled for a wide variety of computer platforms and operating systems with few changes to its source code. Since 2000, C has consistently ranked among the top four languages in the TIOBE index , a measure of the popularity of programming languages. C

6402-438: The language, supported by compilers from AT&T (in particular PCC ) and some other vendors. These included: The large number of extensions and lack of agreement on a standard library , together with the language popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization. During the late 1970s and 1980s, versions of C were implemented for

6499-434: The late 1950s. APL is a language for mathematical computations. Between 1949 and 1951, Heinz Rutishauser proposed Superplan , a high-level language and automatic translator. His ideas were later refined by Friedrich L. Bauer and Klaus Samelson . High-level language design during the formative years of digital computing provided useful programming tools for a variety of applications: Compiler technology evolved from

6596-413: The loop. Break is used to leave the innermost enclosing loop statement and continue is used to skip to its reinitialisation. There is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression. Different from many other languages, control-flow will fall through to

6693-425: The most widely used programming languages, with C compilers available for practically all modern computer architectures and operating systems. The book The C Programming Language , co-authored by the original language designer, served for many years as the de facto standard for the language. C has been standardized since 1989 by the American National Standards Institute (ANSI) and, subsequently, jointly by

6790-408: The need for a strictly defined transformation of the high-level source program into a low-level target program for the digital computer. The compiler could be viewed as a front end to deal with the analysis of the source code and a back end to synthesize the analysis into the target code. Optimization between the front end and back end could produce more efficient target code. Some early milestones in

6887-411: The next case unless terminated by a break . Expressions can use a variety of built-in operators and may contain function calls. The order in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next " sequence point "; sequence points include

6984-475: The one on which the cross-compiler itself runs. A bootstrap compiler is often a temporary compiler, used for compiling a more permanent or better optimised compiler for a language. Related software include decompilers , programs that translate from low-level languages to higher level ones; programs that translate between high-level languages, usually called source-to-source compilers or transpilers ; language rewriters , usually programs that translate

7081-570: The only language processor used to transform source programs. An interpreter is computer software that transforms and then executes the indicated operations. The translation process influences the design of computer languages, which leads to a preference of compilation or interpretation. In theory, a programming language can have both a compiler and an interpreter. In practice, programming languages tend to be associated with just one (a compiler or an interpreter). Theoretical computing concepts developed by scientists, mathematicians, and engineers formed

7178-419: The operating system to a PDP-11 . The original PDP-11 version of Unix was also developed in assembly language. Thompson wanted a programming language for developing utilities for the new platform. He first tried writing a Fortran compiler, but he soon gave up the idea and instead created a cut-down version of the recently developed systems programming language called BCPL . The official description of BCPL

7275-667: The overall effort on Ada development. Other Ada compiler efforts got underway in Britain at the University of York and in Germany at the University of Karlsruhe. In the U. S., Verdix (later acquired by Rational) delivered the Verdix Ada Development System (VADS) to the Army. VADS provided a set of development tools including a compiler. Unix/VADS could be hosted on a variety of Unix platforms such as DEC Ultrix and

7372-511: The performance and the quality of the produced machine code. The middle end contains those optimizations that are independent of the CPU architecture being targeted. The main phases of the middle end include the following: Compiler analysis is the prerequisite for any compiler optimization, and they tightly work together. For example, dependence analysis is crucial for loop transformation . The scope of compiler analysis and optimizations vary greatly; their scope may range from operating within

7469-646: The phase structure of the PQC. The BLISS-11 compiler provided the initial structure. The phases included analyses (front end), intermediate translation to virtual machine (middle end), and translation to the target (back end). TCOL was developed for the PQCC research to handle language specific constructs in the intermediate representation. Variations of TCOL supported various languages. The PQCC project investigated techniques of automated compiler construction. The design concepts proved useful in optimizing compilers and compilers for

7566-652: The preprocessing phase. Comments may appear either between the delimiters /* and */ , or (since C99) following // until the end of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as comment delimiters if they appear inside string or character literals. C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements . Declarations either define new types using keywords such as struct , union , and enum , or assign types to and perhaps reserve storage for new variables, usually by writing

7663-408: The recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that can be radically different. The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7 by Dennis Ritchie and Ken Thompson , incorporating several ideas from colleagues. Eventually, they decided to port

7760-429: The resource limitations of early systems, many early languages were specifically designed so that they could be compiled in a single pass (e.g., Pascal ). In some cases, the design of a language feature may require a compiler to perform more than one pass over the source. For instance, consider a declaration appearing on line 20 of the source which affects the translation of a statement appearing on line 10. In this case,

7857-490: The source code to build an internal representation of the program, called the intermediate representation (IR). It also manages the symbol table , a data structure mapping each symbol in the source code to associated information such as location, type and scope. While the frontend can be a single monolithic function or program, as in a scannerless parser , it was traditionally implemented and analyzed as several phases, which may execute sequentially or concurrently. This method

7954-469: The source language grows in complexity the design may be split into a number of interdependent phases. Separate phases provide design improvements that focus development on the functions in the compilation process. Classifying compilers by number of passes has its background in the hardware resource limitations of computers. Compiling involves performing much work and early computers did not have enough memory to contain one program that did all of this work. As

8051-497: The suffix ‘ f ’ or ‘ l ’ to a function name gives a function that operates on float or long double values respectively. For example: C++ is designed to be compatible with the C programming language , but is not a strict superset of C due to diverging standards. TR1 attempts to reconcile some of these differences through additions to various headers in the C++ library, such as <complex>, <locale>, <cmath>, etc. These changes help to bring C++ more in line with

8148-440: The syntax of "sentences" of a language. It was developed by John Backus and used for the syntax of Algol 60 . The ideas derive from the context-free grammar concepts by linguist Noam Chomsky . "BNF and its extensions have become standard tools for describing the syntax of programming notations. In many cases, parts of compilers are generated automatically from a BNF description." Between 1942 and 1945, Konrad Zuse designed

8245-415: The thing being referenced. C program source text is free-form code. Semicolons terminate statements , while curly braces are used to group statements into blocks . The C language also exhibits the following characteristics: While C does not include certain features found in other languages (such as object orientation and garbage collection ), these can be implemented or emulated, often through

8342-468: The type followed by the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ( { and } , sometimes called "curly brackets") to limit the scope of declarations and to act as a single statement for control structures. As an imperative language, C uses statements to specify actions. The most common statement is an expression statement , consisting of an expression to be evaluated, followed by

8439-476: The urging of Alan Snyder and also in recognition of the usefulness of the file-inclusion mechanisms available in BCPL and PL/I . Its original version provided only included files and simple string replacements: #include and #define of parameterless macros. Soon after that, it was extended, mostly by Mike Lesk and then by John Reiser, to incorporate macros with arguments and conditional compilation . Unix

8536-715: The use of external libraries (e.g., the GLib Object System or the Boehm garbage collector ). Many later languages have borrowed directly or indirectly from C, including C++ , C# , Unix's C shell , D , Go , Java , JavaScript (including transpilers ), Julia , Limbo , LPC , Objective-C , Perl , PHP , Python , Ruby , Rust , Swift , Verilog and SystemVerilog (hardware description languages). These languages have drawn many of their control structures and other basic features from C. Most of them also express highly similar syntax to C, and they tend to combine

8633-541: The use on a K&R C-based compiler of features available only in Standard C. After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive support for international character sets. The C standard

8730-466: Was augmented to include the style used in C++, the K&R interface continued to be permitted, for compatibility with existing source code. C89 is supported by current C compilers, and most modern C code is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on

8827-470: Was available from Boost , and several compiler/library distributors implemented all or some of the components. TR1 is not the complete list of additions to the library that appeared in C++11 . For example, C++11 includes a thread support library that is not available in TR1. The new components were defined in the std::tr1 namespace to distinguish them from the then-current standard library. TR1 includes

8924-432: Was developed for a Digital Equipment Corporation (DEC) PDP-10 computer by W. A. Wulf's Carnegie Mellon University (CMU) research team. The CMU team went on to develop BLISS-11 compiler one year later in 1970. Multics (Multiplexed Information and Computing Service), a time-sharing operating system project, involved MIT , Bell Labs , General Electric (later Honeywell ) and was led by Fernando Corbató from MIT. Multics

9021-706: Was further revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to as " C99 ". It has since been amended three times by Technical Corrigenda. C99 introduced several new features, including inline functions , several new data types (including long long int and a complex type to represent complex numbers ), variable-length arrays and flexible array members , improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity ), and support for one-line comments beginning with // , as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers. C99

9118-511: Was not available at the time, and Thompson modified the syntax to be less 'wordy' and similar to a simplified ALGOL known as SMALGOL. He called the result B , describing it as "BCPL semantics with a lot of SMALGOL syntax". Like BCPL, B had a bootstrapping compiler to facilitate porting to new machines. Ultimately, few utilities were written in B because it was too slow and could not take advantage of PDP-11 features such as byte addressability. In 1971 Ritchie started to improve B, to use

9215-628: Was one of the first operating system kernels implemented in a language other than assembly . Earlier instances include the Multics system (which was written in PL/I ) and Master Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL ) in 1961. In around 1977, Ritchie and Stephen C. Johnson made further changes to the language to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served as

9312-420: Was written in the PL/I language developed by IBM and IBM User Group. IBM's goal was to satisfy business, scientific, and systems programming requirements. There were other languages that could have been considered but PL/I offered the most complete solution even though it had not been implemented. For the first few years of the Multics project, a subset of the language could be compiled to assembly language with

9409-530: Was written, and the language was renamed C. The C compiler and some utilities made with it were included in Version 2 Unix , which is also known as Research Unix . At Version 4 Unix , released in November 1973, the Unix kernel was extensively re-implemented in C. By this time, the C language had acquired some powerful features such as struct types. The preprocessor was introduced around 1973 at

#615384