C# Metrogrid Bound to a Read Only Field
Prototype | Multi-paradigm: imperative (procedural), structured |
---|---|
Designed past | Dennis Ritchie |
Developer | Dennis Ritchie & Bong Labs (creators); ANSI X3J11 (ANSI C); ISO/IEC JTC1/SC22/WG14 (ISO C) |
Commencement appeared | 1972 (1972) [2] |
Stable release | C17 / June 2018 (2018-06) |
Preview release | C2x (N2731) / October 18, 2021 (2021-ten-18) [3] |
Typing field of study | Static, weak, manifest, nominal |
OS | Cantankerous-platform |
Filename extensions | .c, .h |
Website | www www |
Major implementations | |
pcc, GCC, Clang, Intel C, C++Architect, Microsoft Visual C++, Watcom C | |
Dialects | |
Whirlwind, Unified Parallel C, Split-C, Cilk, C* | |
Influenced by | |
B (BCPL, CPL), ALGOL 68,[4] assembly, PL/I, FORTRAN | |
Influenced | |
Numerous: AMPL, AWK, csh, C++, C--, C#, Objective-C, D, Go, Coffee, JavaScript, JS++, Julia, Limbo, LPC, Perl, PHP, Pike, Processing, Python, Band,[5]Rust, Seed7, Vala, Verilog (HDL),[6] Nim, Zig | |
|
C (, equally in the letter c) is a general-purpose, procedural computer programming linguistic communication supporting structured programming, lexical variable telescopic, and recursion, with a static blazon system. By design, C provides constructs that map efficiently to typical machine instructions. It has establish lasting use in applications previously coded in assembly linguistic communication. Such applications include operating systems and various application software for figurer architectures that range from supercomputers to PLCs and embedded systems.
A successor to the programming language B, C was originally developed at Bell Labs by Dennis Ritchie between 1972 and 1973 to construct utilities running on Unix. It was applied to re-implementing the kernel of the Unix operating system.[seven] During the 1980s, C gradually gained popularity. It has become one of the most widely used programming languages,[8] [ix] with C compilers from various vendors available for the bulk of existing computer architectures and operating systems. C has been standardized by ANSI since 1989 (ANSI C) and by the International Organization for Standardization (ISO).
C is an imperative procedural language. Information technology was designed to be compiled to provide low-level access to retentiveness and linguistic communication constructs that map efficiently to car instructions, all with minimal runtime support. Despite its low-level capabilities, the language was designed to encourage cantankerous-platform programming. A standards-compliant C program written with portability in mind can exist compiled for a broad variety of computer platforms and operating systems with few changes to its source code.[10]
Since 2000, C has consistently ranked amongst the top two languages in the TIOBE index, a measure of the popularity of programming languages.[11]
Overview [edit]
Similar near procedural languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion. Its static type arrangement prevents unintended operations. In C, all executable lawmaking is contained within subroutines (as well called "functions", though not strictly in the sense of functional programming). Part parameters are always passed past value (except arrays). Pass-by-reference is simulated in C past explicitly passing pointer values. C plan source text is costless-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements.
The C linguistic communication also exhibits the following characteristics:
- The language has a small, fixed number of keywords, including a total set of control flow primitives:
if/else
,for
,practise/while
,while
, andswitch
. User-defined names are not distinguished from keywords by any kind of sigil. - It has a large number of arithmetic, bitwise, and logic operators:
+
,+=
,++
,&
,||
, etc. - More than ane assignment may be performed in a single statement.
- Functions:
- Function return values can be ignored, when not needed.
- Office and data pointers permit ad hoc run-fourth dimension polymorphism.
- Functions may not be defined inside the lexical scope of other functions.
- Data typing is static, but weakly enforced; all data has a blazon, simply implicit conversions are possible.
- Declaration syntax mimics usage context. C has no "define" keyword; instead, a statement outset with the name of a blazon is taken as a announcement. In that location is no "part" keyword; instead, a function is indicated by the presence of a parenthesized argument list.
- User-divers (typedef) and chemical compound types are possible.
- Heterogeneous amass data types (
struct
) permit related data elements to exist accessed and assigned as a unit. - Wedlock is a structure with overlapping members; only the last member stored is valid.
- Array indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects: they cannot be assigned or compared using unmarried congenital-in operators. There is no "assortment" keyword in use or definition; instead, square brackets indicate arrays syntactically, for instance
month[eleven]
. - Enumerated types are possible with the
enum
keyword. They are freely interconvertible with integers. - Strings are not a distinct information type, but are conventionally implemented as null-terminated character arrays.
- Heterogeneous amass data types (
- Low-level access to computer memory is possible by converting machine addresses to typed pointers.
- Procedures (subroutines not returning values) are a special instance of role, with an untyped return type
void
. - A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
- In that location is a basic form of modularity: files tin can be compiled separately and linked together, with control over which functions and information objects are visible to other files via
static
andextern
attributes. - Circuitous functionality such equally I/O, cord manipulation, and mathematical functions are consistently delegated to library routines.
While C does not include certain features found in other languages (such every bit object orientation and garbage drove), these tin can be implemented or emulated, frequently through the use of external libraries (e.one thousand., the GLib Object Arrangement or the Boehm garbage collector).
Relations to other languages [edit]
Many later languages have borrowed direct or indirectly from C, including C++, C#, Unix's C shell, D, Go, Coffee, JavaScript (including transpilers), Julia, Limbo, LPC, Objective-C, Perl, PHP, Python, Ruby, Rust, Swift, Verilog and SystemVerilog (hardware clarification languages).[6] These languages accept drawn many of their control structures and other basic features from C. Nigh of them (Python being a dramatic exception) as well express highly similar syntax to C, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, information models, and semantics that can be radically unlike.
History [edit]
Early developments [edit]
Year | C Standard[ten] |
---|---|
1972 | Birth |
1978 | K&R C |
1989/1990 | ANSI C and ISO C |
1999 | C99 |
2011 | C11 |
2017 | C17 |
TBD | C2x |
The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-vii by Dennis Ritchie and Ken Thompson, incorporating several ideas from colleagues. Eventually, they decided to port the operating arrangement to a PDP-11. The original PDP-11 version of Unix was also developed in assembly language.[7]
Thompson desired a programming language to brand utilities for the new platform. At first, he tried to make a Fortran compiler, but soon gave up the idea. Instead, he created a cut-down version of the recently adult BCPL systems programming language. The official description of BCPL was not available at the fourth dimension,[12] and Thompson modified the syntax to be less wordy, producing the like but somewhat simpler B.[7] Still, few utilities were ultimately written in B considering it was as well tedious, and B could not take advantage of PDP-eleven features such every bit byte addressability.
In 1972, Ritchie started to amend B, most notably adding data typing for variables, which resulted in creating a new language C.[13] The C compiler and some utilities made with information technology were included in Version 2 Unix.[14]
At Version 4 Unix, released in Nov 1973, the Unix kernel was extensively re-implemented in C.[vii] By this time, the C language had caused some powerful features such as struct
types.
The preprocessor was introduced around 1973 at 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 elementary cord replacements: #include
and #define
of parameterless macros. Presently after that, it was extended, more often than not past Mike Lesk and then past John Reiser, to comprise macros with arguments and conditional compilation.[7]
Unix was one of the start operating system kernels implemented in a language other than assembly. Earlier instances include the Multics organization (which was written in PL/I) and Primary Control Program (MCP) for the Burroughs B5000 (which was written in ALGOL) in 1961. In effectually 1977, Ritchie and Stephen C. Johnson made further changes to the linguistic communication to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served every bit the basis for several implementations of C on new platforms.[xiii]
K&R C [edit]
In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language.[1] This book, known to C programmers as Chiliad&R, served for many years every bit an breezy specification of the language. The version of C that it describes is usually referred to as "One thousand&R C". As this was released in 1978, it is also referred to every bit C78.[xv] The second edition of the book[sixteen] covers the after ANSI C standard, described below.
K&R introduced several linguistic communication features:
- Standard I/O library
-
long int
data type -
unsigned int
data type - Compound assignment operators of the class
=op
(such equally=-
) were changed to the classop=
(that is,-=
) to remove the semantic ambiguity created by constructs such asi=-10
, which had been interpreted asi =- 10
(decrementi
by 10) instead of the possibly intendedi = -x
(allowi
be −x).
Fifty-fifty after the publication of the 1989 ANSI standard, for many years Grand&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 employ, and because advisedly written Grand&R C code tin 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 the office definition; functions used without prior declaration were presumed to return blazon int
.
For example:
long some_function (); /* int */ other_function (); /* int */ calling_function () { long test1 ; register /* int */ test2 ; test1 = some_function (); if ( test1 > ane ) test2 = 0 ; else test2 = other_function (); return test2 ; }
The int
type specifiers which are commented out could be omitted in Grand&R C, simply are required in later standards.
Since 1000&R function declarations did not include any information about office arguments, function parameter type checks were not performed, although some compilers would effect a warning bulletin if a local function was called with the incorrect number of arguments, or if multiple calls to an external function used dissimilar numbers or types of arguments. Separate tools such as Unix'due south lint utility were adult that (amidst 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 the language, supported by compilers from AT&T (in particular PCC[17]) and another vendors. These included:
-
void
functions (i.east., functions with no render value) - functions returning
struct
ormatrimony
types (rather than pointers) - assignment for
struct
data types - enumerated types
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.
ANSI C and ISO C [edit]
During the late 1970s and 1980s, versions of C were implemented for 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 Constitute (ANSI) formed a committee, X3J11, to plant a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the not-portable portion of the Unix C library was handed off to the IEEE working grouping 1003 to become the ground for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Language C". This version of the linguistic communication is often referred to every bit 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 is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the aforementioned programming linguistic communication.
ANSI, like other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained past 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 the aims of the C standardization process was to produce a superset of Grand&R C, incorporating many of the later introduced unofficial features. The standards committee also included several additional features such equally role prototypes (borrowed from C++), void
pointers, back up for international character sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the way used in C++, the K&R interface continued to be permitted, for compatibility with existing source code.
C89 is supported past current C compilers, and most modern C lawmaking is based on it. Whatever program written merely 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 simply on a certain platform or with a particular compiler, due, for example, to the apply of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such every bit the verbal size of data types and byte endianness.
In cases where lawmaking must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__
macro can be used to separate the code into Standard and Chiliad&R sections to forestall the apply on a K&R C-based compiler of features bachelor only in Standard C.
After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995, Normative Subpoena 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 all-encompassing support for international character sets.[18]
C99 [edit]
The C standard was farther revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is normally referred to as "C99". Information technology has since been amended three times past Technical Corrigenda.[19]
C99 introduced several new features, including inline functions, several new data types (including long long int
and a circuitous
type to stand for complex numbers), variable-length arrays and flexible assortment members, improved support for IEEE 754 floating point, back up for variadic macros (macros of variable arity), and back up for one-line comments beginning with //
, equally in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.
C99 is for the most function backward uniform with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int
implicitly causeless. A standard macro __STDC_VERSION__
is divers with value 199901L
to signal that C99 back up is available. GCC, Solaris Studio, and other C compilers now back up many or all of the new features of C99. The C compiler in Microsoft Visual C++, however, implements the C89 standard and those parts of C99 that are required for compatibility with C++eleven.[20] [ needs update ]
In add-on, support for Unicode identifiers (variable / function names) in the form of escaped characters (eastward.g. \U0001f431
) is at present required. Support for raw Unicode names is optional.
C11 [edit]
In 2007, work began on another revision of the C standard, informally called "C1X" until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested past existing implementations.
The C11 standard adds numerous new features to C and the library, including type generic macros, bearding structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It likewise makes some portions of the existing C99 library optional, and improves compatibility with C++. The standard macro __STDC_VERSION__
is defined as 201112L
to betoken that C11 support is bachelor.
C17 [edit]
Published in June 2018, C17 is the current standard for the C programming language. Information technology introduces no new language features, merely technical corrections, and clarifications to defects in C11. The standard macro __STDC_VERSION__
is defined as 201710L
.
C2x [edit]
C2x is an informal name for the next (afterwards C17) major C language standard revision. Information technology is expected to be voted on in 2023 and would therefore be chosen C23.[21] [ ameliorate source needed ]
Embedded C [edit]
Historically, embedded C programming requires nonstandard extensions to the C linguistic communication in lodge to back up exotic features such every bit fixed-point arithmetic, multiple distinct memory banks, and basic I/O operations.
In 2008, the C Standards Committee published a technical study extending the C language[22] to accost these bug by providing a common standard for all implementations to adhere to. It includes a number of features not bachelor in normal C, such every bit fixed-betoken arithmetic, named address spaces, and basic I/O hardware addressing.
Syntax [edit]
C has a formal grammer specified by the C standard.[23] Line endings are generally not significant in C; however, line boundaries practice have significance during the preprocessing stage. Comments may appear either between the delimiters /*
and */
, or (since C99) following //
until the cease 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 graphic symbol literals.[24]
C source files contain declarations and function definitions. Part definitions, in plough, comprise declarations and statements. Declarations either define new types using keywords such every bit struct
, union
, and enum
, or assign types to and perhaps reserve storage for new variables, unremarkably by writing the blazon followed by the variable proper name. Keywords such every bit 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 human action as a unmarried argument for control structures.
As an imperative language, C uses statements to specify actions. The nigh common argument is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side effect of the evaluation, functions may be called and variables may be 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 past 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 tin can be omitted. break
and continue
tin can exist used to leave the innermost enclosing loop statement or skip to its reinitialization. At that place is also a non-structured goto
statement which branches directly to the designated characterization within the part. switch
selects a example
to be executed based on the value of an integer expression.
Expressions tin can use a diversity of congenital-in operators and may comprise role calls. The social club in which arguments to functions and operands to nearly operators are evaluated is unspecified. The evaluations may fifty-fifty exist interleaved. All the same, all side effects (including storage to variables) will occur before the next "sequence indicate"; sequence points include the stop of each expression statement, and the entry to and return from each function telephone call. Sequence points also occur during evaluation of expressions containing certain operators (&&
, ||
, ?:
and the comma operator). This permits a high degree of object code optimization by the compiler, simply requires C programmers to take more care to obtain reliable results than is needed for other programming languages.
Kernighan and Ritchie say in the Introduction of The C Programming Linguistic communication: "C, similar any other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be better."[25] The C standard did non attempt to correct many of these blemishes, considering of the impact of such changes on already existing software.
Character set up [edit]
The basic C source character gear up includes the post-obit characters:
- Lowercase and uppercase letters of ISO Basic Latin Alphabet:
a
–z
A
–Z
- Decimal digits:
0
–9
- Graphic characters:
! " # % & ' ( ) * + , - . / : ; < = > ? [ \ ] ^ _ { | } ~
- Whitespace characters: space, horizontal tab, vertical tab, form feed, newline
Newline indicates the terminate of a text line; information technology demand not stand for to an actual unmarried grapheme, although for convenience C treats it equally i.
Additional multi-byte encoded characters may be used in string literals, just they are not entirely portable. The latest C standard (C11) allows multi-national Unicode characters to be embedded portably within C source text by using \uXXXX
or \UXXXXXXXX
encoding (where the Ten
denotes a hexadecimal character), although this feature is not yet widely implemented.
The basic C execution character ready contains the same characters, along with representations for warning, backspace, and carriage return. Run-fourth dimension back up for extended character sets has increased with each revision of the C standard.
Reserved words [edit]
C89 has 32 reserved words, also known as keywords, which are the words that cannot be used for any purposes other than those for which they are predefined:
-
automobile
-
interruption
-
case
-
char
-
const
-
continue
-
default
-
practice
-
double
-
else
-
enum
-
extern
-
bladder
-
for
-
goto
-
if
-
int
-
long
-
register
-
render
-
short
-
signed
-
sizeof
-
static
-
struct
-
switch
-
typedef
-
union
-
unsigned
-
void
-
volatile
-
while
C99 reserved five more words:
-
_Bool
-
_Complex
-
_Imaginary
-
inline
-
restrict
C11 reserved 7 more than words:[26]
-
_Alignas
-
_Alignof
-
_Atomic
-
_Generic
-
_Noreturn
-
_Static_assert
-
_Thread_local
Most of the recently reserved words begin with an underscore followed past a capital letter, considering identifiers of that course were previously reserved by the C standard for utilise only by implementations. Since existing plan source code should not have been using these identifiers, it would not be afflicted when C implementations started supporting these extensions to the programming language. Some standard headers do define more user-friendly synonyms for underscored identifiers. The language previously included a reserved word called entry
, only this was seldom implemented, and has at present been removed equally a reserved word.[27]
Operators [edit]
C supports a rich set up of operators, which are symbols used within an expression to specify the manipulations to exist performed while evaluating that expression. C has operators for:
- arithmetics:
+
,-
,*
,/
,%
- consignment:
=
- augmented assignment:
+=
,-=
,*=
,/=
,%=
,&=
,|=
,^=
,<<=
,>>=
- bitwise logic:
~
,&
,|
,^
- bitwise shifts:
<<
,>>
- boolean logic:
!
,&&
,||
- conditional evaluation:
? :
- equality testing:
==
,!=
- calling functions:
( )
- increment and decrement:
++
,--
- fellow member option:
.
,->
- object size:
sizeof
- lodge relations:
<
,<=
,>
,>=
- reference and dereference:
&
,*
,[ ]
- sequencing:
,
- subexpression grouping:
( )
- type conversion:
(typename)
C uses the operator =
(used in mathematics to express equality) to betoken assignment, following the precedent of Fortran and PL/I, but dissimilar ALGOL and its derivatives. C uses the operator ==
to test for equality. The similarity between these two operators (consignment and equality) may result in the accidental utilise of one in identify of the other, and in many cases, the mistake does non produce an error message (although some compilers produce warnings). For case, the conditional expression if (a == b + 1)
might mistakenly be written as if (a = b + 1)
, which volition be evaluated as true if a
is non zero later the assignment.[28]
The C operator precedence is not always intuitive. For example, the operator ==
binds more tightly than (is executed prior to) the operators &
(bitwise AND) and |
(bitwise OR) in expressions such as x & 1 == 0
, which must be written as (x & 1) == 0
if that is the coder'south intent.[29]
"Hullo, globe" example [edit]
The "hello, globe" example, which appeared in the get-go edition of K&R, has become the model for an introductory plan in near programming textbooks. The plan prints "hi, world" to the standard output, which is usually a terminal or screen display.
The original version was:[30]
main () { printf ( "hello, globe \n " ); }
A standard-befitting "hello, globe" program is:[a]
#include <stdio.h> int main ( void ) { printf ( "hello, world \due north " ); }
The first line of the plan contains a preprocessing directive, indicated past #include
. This causes the compiler to replace that line with the entire text of the stdio.h
standard header, which contains declarations for standard input and output functions such equally printf
and scanf
. The angle brackets surrounding stdio.h
indicate that stdio.h
is located using a search strategy that prefers headers provided with the compiler to other headers having the same name, as opposed to double quotes which typically include local or project-specific header files.
The next line indicates that a role named main
is existence defined. The chief
function serves a special purpose in C programs; the run-time environment calls the main
function to brainstorm programme execution. The type specifier int
indicates that the value that is returned to the invoker (in this case the run-time surroundings) as a consequence of evaluating the primary
office, is an integer. The keyword void
equally a parameter list indicates that this function takes no arguments.[b]
The opening curly brace indicates the beginning of the definition of the master
function.
The side by side line calls (diverts execution to) a function named printf
, which in this case is supplied from a system library. In this telephone call, the printf
function is passed (provided with) a single argument, the address of the first character in the cord literal "hullo, world\n"
. The string literal is an unnamed array with elements of type char
, gear up up automatically by the compiler with a final 0-valued grapheme to mark the stop of the array (printf
needs to know this). The \northward
is an escape sequence that C translates to a newline character, which on output signifies the end of the current line. The return value of the printf
part is of blazon int
, just it is silently discarded since it is non used. (A more careful program might examination the return value to determine whether or non the printf
function succeeded.) The semicolon ;
terminates the statement.
The closing curly brace indicates the cease of the code for the master
function. According to the C99 specification and newer, the primary
function, different whatsoever other function, will implicitly render a value of 0
upon reaching the }
that terminates the office. (Formerly an explicit return 0;
statement was required.) This is interpreted by the run-fourth dimension organisation as an exit code indicating successful execution.[31]
Information types [edit]
The type system in C is static and weakly typed, which makes information technology similar to the type organisation of ALGOL descendants such equally Pascal.[32] In that location are born types for integers of various sizes, both signed and unsigned, floating-point numbers, and enumerated types (enum
). Integer type char
is oftentimes used for single-byte characters. C99 added a boolean datatype. There are also derived types including arrays, pointers, records (struct
), and unions (marriage
).
C is often used in low-level systems programming where escapes from the type organisation may be necessary. The compiler attempts to ensure type correctness of nigh expressions, but the programmer tin override the checks in various ways, either by using a blazon cast to explicitly convert a value from one blazon to another, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way.
Some find C'southward declaration syntax unintuitive, particularly for function pointers. (Ritchie's thought was to declare identifiers in contexts resembling their use: "declaration reflects utilise".)[33]
C's usual arithmetic conversions allow for efficient code to exist generated, but can sometimes produce unexpected results. For instance, a comparison of signed and unsigned integers of equal width requires a conversion of the signed value to unsigned. This can generate unexpected results if the signed value is negative.
Pointers [edit]
C supports the use of pointers, a type of reference that records the accost or location of an object or role in retention. Pointers can exist dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-inside-word field), simply since a pointer's type includes the blazon of the thing pointed to, expressions including pointers can be type-checked at compile time. Pointer arithmetic is automatically scaled by the size of the pointed-to data type. Pointers are used for many purposes in C. Text strings are usually manipulated using pointers into arrays of characters. Dynamic retention allotment is performed using pointers. Many information types, such every bit trees, are ordinarily implemented as dynamically allocated struct
objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to college-order functions (such equally qsort or bsearch) or as callbacks to be invoked by result handlers.[31]
A nada pointer value explicitly points to no valid location. Dereferencing a nada pointer value is undefined, ofttimes resulting in a segmentation error. Null arrow values are useful for indicating special cases such as no "side by side" pointer in the final node of a linked list, or equally an error indication from functions returning pointers. In advisable contexts in source code, such as for assigning to a pointer variable, a null pointer constant tin can exist written as 0
, with or without explicit casting to a pointer type, or equally the Naught
macro defined past several standard headers. In conditional contexts, nothing pointer values evaluate to fake, while all other arrow values evaluate to true.
Void pointers (void *
) point to objects of unspecified type, and can therefore exist used as "generic" data pointers. Since the size and type of the pointed-to object is non known, void pointers cannot be dereferenced, nor is pointer arithmetics on them allowed, although they tin easily exist (and in many contexts implicitly are) converted to and from any other object pointer type.[31]
Careless use of pointers is potentially dangerous. Because they are typically unchecked, a arrow variable can be made to point to whatsoever arbitrary location, which can cause undesirable effects. Although properly used pointers betoken to safe places, they can exist made to bespeak to unsafe places by using invalid pointer arithmetic; the objects they point to may go on to be used after deallocation (dangling pointers); they may be used without having been initialized (wild pointers); or they may exist directly assigned an unsafe value using a cast, wedlock, or through another corrupt arrow. In general, C is permissive in allowing manipulation of and conversion betwixt pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more than restrictive reference types.
Arrays [edit]
Array types in C are traditionally of a stock-still, static size specified at compile time. The more recent C99 standard also allows a form of variable-length arrays. Nevertheless, it is also possible to allocate a block of memory (of arbitrary size) at run-fourth dimension, using the standard library'southward malloc
part, and treat it as an array.
Since arrays are always accessed (in effect) via pointers, array accesses are typically non checked against the underlying assortment size, although some compilers may provide bounds checking as an pick.[34] [35] Assortment bounds violations are therefore possible and tin pb to various repercussions, including illegal memory accesses, corruption of data, buffer overruns, and run-fourth dimension exceptions.
C does non take a special provision for declaring multi-dimensional arrays, merely rather relies on recursion within the type system to declare arrays of arrays, which effectively accomplishes the same thing. The alphabetize values of the resulting "multi-dimensional assortment" tin can be thought of equally increasing in row-major order. Multi-dimensional arrays are unremarkably used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C array is well suited to this detail task. Still, in early versions of C the bounds of the array must be known fixed values or else explicitly passed to whatever subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this was to allocate the array with an additional "row vector" of pointers to the columns.) C99 introduced "variable-length arrays" which address this consequence.
The following example using mod C (C99 or subsequently) shows allotment of a ii-dimensional array on the heap and the use of multi-dimensional array indexing for accesses (which tin can use bounds-checking on many C compilers):
int func ( int N , int M ) { float ( * p )[ Due north ][ K ] = malloc ( sizeof * p ); if ( ! p ) render -1 ; for ( int i = 0 ; i < Due north ; i ++ ) for ( int j = 0 ; j < M ; j ++ ) ( * p )[ i ][ j ] = i + j ; print_array ( N , M , p ); gratis ( p ); return 1 ; }
Array–pointer interchangeability [edit]
The subscript annotation x[i]
(where x
designates a pointer) is syntactic sugar for *(x+i)
.[36] Taking advantage of the compiler's knowledge of the pointer type, the accost that x + i
points to is non the base address (pointed to by x
) incremented past i
bytes, but rather is divers to exist the base accost incremented by i
multiplied past the size of an element that x
points to. Thus, ten[i]
designates the i+i
th element of the array.
Furthermore, in most expression contexts (a notable exception is as operand of sizeof
), an expression of array type is automatically converted to a arrow to the assortment'southward offset chemical element. This implies that an array is never copied as a whole when named as an argument to a function, but rather but the address of its outset element is passed. Therefore, although function calls in C apply pass-by-value semantics, arrays are in upshot passed by reference.
The total size of an array x
can be determined by applying sizeof
to an expression of array type. The size of an chemical element tin can exist determined by applying the operator sizeof
to any dereferenced element of an assortment A
, equally in n = sizeof A[0]
. This, the number of elements in a declared array A
tin be adamant every bit sizeof A / sizeof A[0]
. Notation, that if simply a pointer to the first chemical element is available equally information technology is often the case in C code because of the automatic conversion described above, the information nearly the total type of the array and its length are lost.
Retentivity management [edit]
1 of the well-nigh important functions of a programming linguistic communication is to provide facilities for managing memory and the objects that are stored in memory. C provides three distinct ways to classify retentiveness for objects:[31]
- Static memory allocation: infinite for the object is provided in the binary at compile-time; these objects take an extent (or lifetime) as long as the binary which contains them is loaded into memory.
- Automated retention resource allotment: temporary objects can be stored on the stack, and this space is automatically freed and reusable after the block in which they are declared is exited.
- Dynamic memory allotment: blocks of memory of capricious size can exist requested at run-time using library functions such as
malloc
from a region of retentivity called the heap; these blocks persist until subsequently freed for reuse past calling the library functionrealloc
orfree
These three approaches are appropriate in dissimilar situations and accept various trade-offs. For instance, static retentivity allocation has little allocation overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially have a not bad deal of overhead for both resource allotment and deallocation. The persistent nature of static objects is useful for maintaining state data across part calls, automatic allotment is piece of cake to use but stack infinite is typically much more limited and transient than either static memory or heap space, and dynamic retention allotment allows convenient allocation of objects whose size is known but at run-time. Nigh C programs make extensive use of all three.
Where possible, automated or static allocation is usually simplest because the storage is managed by the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. Nonetheless, many information structures can change in size at runtime, and since static allocations (and automatic allocations before C99) must have a stock-still size at compile-time, there are many situations in which dynamic allocation is necessary.[31] Prior to the C99 standard, variable-sized arrays were a mutual example of this. (See the commodity on malloc
for an example of dynamically allocated arrays.) Unlike automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a zip pointer value) when the required storage cannot be allocated. (Static allotment that is likewise large is usually detected by the linker or loader, earlier the program can even begin execution.)
Unless otherwise specified, static objects contain null or null arrow values upon programme startup. Automatically and dynamically allocated objects are initialized only if an initial value is explicitly specified; otherwise they initially have indeterminate values (typically, whatever scrap blueprint happens to be present in the storage, which might non even represent a valid value for that type). If the plan attempts to admission an uninitialized value, the results are undefined. Many modernistic compilers try to detect and warn about this problem, merely both simulated positives and false negatives can occur.
Heap memory allotment has to be synchronized with its actual usage in whatever plan to be reused every bit much as possible. For example, if the only pointer to a heap memory resource allotment goes out of scope or has its value overwritten before it is deallocated explicitly, and so that retention cannot exist recovered for later on reuse and is essentially lost to the program, a phenomenon known every bit a memory leak. Conversely, it is possible for memory to be freed, only is referenced subsequently, leading to unpredictable results. Typically, the failure symptoms announced in a portion of the program unrelated to the code that causes the fault, making it difficult to diagnose the failure. Such bug are ameliorated in languages with automatic garbage collection.
Libraries [edit]
The C programming language uses libraries as its primary method of extension. In C, a library is a set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions independent inside the library that may be used past a program, and declarations of special data types and macro symbols used with these functions. In guild for a program to utilise a library, it must include the library's header file, and the library must exist linked with the plan, which in many cases requires compiler flags (e.chiliad., -lm
, shorthand for "link the math library").[31]
The virtually common C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation (implementations which target limited environments such as embedded systems may provide only a subset of the standard library). This library supports stream input and output, memory allocation, mathematics, character strings, and time values. Several split standard headers (for example, stdio.h
) specify the interfaces for these and other standard library facilities.
Another common set of C library functions are those used by applications specifically targeted for Unix and Unix-like systems, especially functions which provide an interface to the kernel. These functions are detailed in various standards such as POSIX and the Single UNIX Specification.
Since many programs have been written in C, in that location are a wide diversity of other libraries bachelor. Libraries are ofttimes written in C because C compilers generate efficient object code; programmers then create interfaces to the library and then that the routines tin can be used from higher-level languages like Java, Perl, and Python.[31]
File handling and streams [edit]
File input and output (I/O) is not role of the C language itself but instead is handled by libraries (such equally the C standard library) and their associated header files (e.g. stdio.h
). File handling is more often than not implemented through high-level I/O which works through streams. A stream is from this perspective a information flow that is independent of devices, while a file is a concrete device. The loftier-level I/O is done through the association of a stream to a file. In the C standard library, a buffer (a memory area or queue) is temporarily used to shop information before it's sent to the terminal destination. This reduces the time spent waiting for slower devices, for example a hard bulldoze or solid state bulldoze. Low-level I/O functions are not part of the standard C library[ clarification needed ] merely are generally office of "bare metal" programming (programming that's independent of whatever operating arrangement such as virtually embedded programming). With few exceptions, implementations include low-level I/O.
Language tools [edit]
A number of tools have been developed to help C programmers detect and fix statements with undefined beliefs or possibly erroneous expressions, with greater rigor than that provided by the compiler. The tool lint was the outset such, leading to many others.
Automatic source lawmaking checking and auditing are beneficial in any language, and for C many such tools be, such every bit Lint. A common practice is to apply Lint to detect questionable code when a programme is first written. Once a plan passes Lint, it is then compiled using the C compiler. Also, many compilers tin optionally warn about syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary set of guidelines to avoid such questionable code, developed for embedded systems.[37]
There are also compilers, libraries, and operating arrangement level mechanisms for performing actions that are not a standard part of C, such as bounds checking for arrays, detection of buffer overflow, serialization, dynamic retentivity tracking, and automated garbage drove.
Tools such equally Purify or Valgrind and linking with libraries containing special versions of the memory allotment functions tin can assistance uncover runtime errors in retentiveness usage.
Uses [edit]
C is widely used for systems programming in implementing operating systems and embedded system applications,[38] because C code, when written for portability, can be used for most purposes, yet when needed, system-specific code tin can be used to access specific hardware addresses and to perform type punning to match externally imposed interface requirements, with a low run-time demand on system resources.
C tin can be used for website programming using the Mutual Gateway Interface (CGI) equally a "gateway" for information between the Web awarding, the server, and the browser.[39] C is often called over interpreted languages because of its speed, stability, and near-universal availability.[40]
A consequence of C's wide availability and efficiency is that compilers, libraries and interpreters of other programming languages are frequently implemented in C. For example, the reference implementations of Python, Perl, Reddish, and PHP are written in C.
C enables programmers to create efficient implementations of algorithms and data structures, because the layer of abstraction from hardware is thin, and its overhead is low, an important criterion for computationally intensive programs. For instance, the GNU Multiple Precision Arithmetics Library, the GNU Scientific Library, Mathematica, and MATLAB are completely or partially written in C.
C is sometimes used as an intermediate language by implementations of other languages. This approach may exist used for portability or convenience; past using C as an intermediate language, additional automobile-specific code generators are non necessary. C has some features, such as line-number preprocessor directives and optional superfluous commas at the cease of initializer lists, that support compilation of generated code. However, some of C'southward shortcomings have prompted the development of other C-based languages specifically designed for employ as intermediate languages, such equally C--.
C has as well been widely used to implement terminate-user applications. However, such applications can also be written in newer, higher-level languages.
[edit]
C has both direct and indirectly influenced many later languages such equally C#, D, Become, Java, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix's C vanquish.[42] The most pervasive influence has been syntactical; all of the languages mentioned combine the argument and (more than or less recognizably) expression syntax of C with blazon systems, data models, and/or large-scale program structures that differ from those of C, sometimes radically.
Several C or nearly-C interpreters exist, including Ch and CINT, which can also be used for scripting.
When object-oriented programming languages became popular, C++ and Objective-C were two unlike extensions of C that provided object-oriented capabilities. Both languages were originally implemented as source-to-source compilers; source code was translated into C, so compiled with a C compiler.[43]
The C++ programming linguistic communication (originally named "C with Classes") was devised by Bjarne Stroustrup as an approach to providing object-oriented functionality with a C-similar syntax.[44] C++ adds greater typing force, scoping, and other tools useful in object-oriented programming, and permits generic programming via templates. Most a superset of C, C++ now supports almost of C, with a few exceptions.
Objective-C was originally a very "thin" layer on meridian of C, and remains a strict superset of C that permits object-oriented programming using a hybrid dynamic/static typing paradigm. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations, and part calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk.
In improver to C++ and Objective-C, Ch, Cilk, and Unified Parallel C are virtually supersets of C.
See also [edit]
- Compatibility of C and C++
- Comparison of Pascal and C
- Comparison of programming languages
- International Obfuscated C Code Competition
- Listing of C-based programming languages
- List of C compilers
Notes [edit]
- ^ The original instance lawmaking will compile on most modern compilers that are non in strict standard compliance mode, but it does not fully conform to the requirements of either C89 or C99. In fact, C99 requires that a diagnostic bulletin be produced.
- ^ The
chief
part really has two arguments,int argc
andchar *argv[]
, respectively, which tin be used to handle control line arguments. The ISO C standard (section 5.1.2.2.1) requires both forms ofmain
to be supported, which is special handling not afforded to any other function.
References [edit]
- ^ a b Kernighan, Brian West.; Ritchie, Dennis Yard. (February 1978). The C Programming Language (1st ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110163-0.
- ^ Ritchie (1993): "Thompson had made a brief attempt to produce a organization coded in an early version of C—before structures—in 1972, but gave up the effort."
- ^ Fruderica (December 13, 2020). "History of C". The cppreference.com. Archived from the original on October 24, 2020. Retrieved October 24, 2020.
- ^ Ritchie (1993): "The scheme of blazon limerick adopted by C owes considerable debt to Algol 68, although information technology did not, perhaps, emerge in a form that Algol's adherents would approve of."
- ^ Ring Team (Oct 23, 2021). "The Ring programming linguistic communication and other languages". band-lang.net.
- ^ a b "Verilog HDL (and C)" (PDF). The Research School of Computer Science at the Australian National University. June 3, 2010. Archived from the original (PDF) on November 6, 2013. Retrieved Baronial nineteen, 2013.
1980s: ; Verilog showtime introduced ; Verilog inspired past the C programming language
- ^ a b c d e Ritchie (1993)
- ^ "Programming Language Popularity". 2009. Archived from the original on January xvi, 2009. Retrieved January xvi, 2009.
- ^ "TIOBE Programming Customs Index". 2009. Archived from the original on May 4, 2009. Retrieved May half-dozen, 2009.
- ^ a b "History of C". en.cppreference.com. Archived from the original on May 29, 2018. Retrieved May 28, 2018.
- ^ "TIOBE Index for October 2021". Retrieved October seven, 2021.
- ^ Ritchie, Dennis. "BCPL to B to C". Archived from the original on Dec 12, 2019. Retrieved September ten, 2019.
- ^ a b Johnson, S. C.; Ritchie, D. M. (1978). "Portability of C Programs and the UNIX Arrangement". Bell System Tech. J. 57 (6): 2021–2048. CiteSeerX10.1.1.138.35. doi:ten.1002/j.1538-7305.1978.tb02141.x. S2CID 17510065. (Note: The PDF is an OCR scan of the original, and contains a rendering of "IBM 370" as "IBM 310".)
- ^ McIlroy, M. D. (1987). A Research Unix reader: annotated excerpts from the Programmer'south Transmission, 1971–1986 (PDF) (Technical report). CSTR. Bell Labs. p. ten. 139. Archived (PDF) from the original on November 11, 2017. Retrieved Feb ane, 2015.
- ^ "C manual pages". FreeBSD Miscellaneous Information Transmission (FreeBSD thirteen.0 ed.). May 30, 2011. Archived from the original on January 21, 2021. Retrieved Jan 15, 2021. [1] Archived January 21, 2021, at the Wayback Machine
- ^ Kernighan, Brian W.; Ritchie, Dennis M. (March 1988). The C Programming Language (2nd ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-13-110362-7.
- ^ Stroustrup, Bjarne (2002). Sibling rivalry: C and C++ (PDF) (Report). AT&T Labs. Archived (PDF) from the original on Baronial 24, 2014. Retrieved April 14, 2014.
- ^ C Integrity. International Organization for Standardization. March 30, 1995. Archived from the original on July 25, 2018. Retrieved July 24, 2018.
- ^ "JTC1/SC22/WG14 – C". Home page. ISO/IEC. Archived from the original on Feb 12, 2018. Retrieved June 2, 2011.
- ^ Andrew Binstock (October 12, 2011). "Interview with Herb Sutter". Dr. Dobbs. Archived from the original on August 2, 2013. Retrieved September 7, 2013.
- ^ "Revised C23 Schedule WG 14 N 2759" (PDF). www.open-std.org. Archived (PDF) from the original on June 24, 2021. Retrieved Oct 10, 2021.
- ^ "TR 18037: Embedded C" (PDF). ISO / IEC. Archived (PDF) from the original on February 25, 2021. Retrieved July 26, 2011.
- ^ Harbison, Samuel P.; Steele, Guy L. (2002). C: A Reference Manual (fifth ed.). Englewood Cliffs, NJ: Prentice Hall. ISBN978-0-xiii-089592-9. Contains a BNF grammar for C.
- ^ Kernighan & Ritchie (1996), p. 192.
- ^ Kernighan & Ritchie (1978), p. iii.
- ^ "ISO/IEC 9899:201x (ISO C11) Committee Draft" (PDF). Archived (PDF) from the original on December 22, 2017. Retrieved September sixteen, 2011.
- ^ Kernighan & Ritchie (1996), pp. 192, 259.
- ^ "ten Common Programming Mistakes in C++". Cs.ucr.edu. Archived from the original on Oct 21, 2008. Retrieved June 26, 2009.
- ^ Schultz, Thomas (2004). C and the 8051 (3rd ed.). Otsego, MI: PageFree Publishing Inc. p. xx. ISBN978-1-58961-237-two. Archived from the original on July 29, 2020. Retrieved February 10, 2012.
- ^ Kernighan & Ritchie (1978), p. 6.
- ^ a b c d east f g Klemens, Ben (2013). 21st Century C. O'Reilly Media. ISBN978-1-4493-2714-9.
- ^ Feuer, Alan R.; Gehani, Narain H. (March 1982). "Comparing of the Programming Languages C and Pascal". ACM Computing Surveys. fourteen (1): 73–92. doi:ten.1145/356869.356872. S2CID 3136859.
- ^ Kernighan & Ritchie (1996), p. 122.
- ^ For example, gcc provides _FORTIFY_SOURCE. "Security Features: Compile Time Buffer Checks (FORTIFY_SOURCE)". fedoraproject.org. Archived from the original on January vii, 2007. Retrieved August five, 2012.
- ^ เอี่ยมสิริวงศ์, โอภาศ (2016). Programming with C. Bangkok, Thailand: SE-Instruction PUBLIC COMPANY Express. pp. 225–230. ISBN978-616-08-2740-four.
- ^ Raymond, Eric S. (Oct 11, 1996). The New Hacker's Dictionary (third ed.). MIT Press. p. 432. ISBN978-0-262-68092-ix. Archived from the original on Nov 12, 2012. Retrieved August five, 2012.
- ^ "Man Page for lint (freebsd Section 1)". unix.com. May 24, 2001. Retrieved July fifteen, 2014.
- ^ Dale, Nell B.; Weems, Chip (2014). Programming and problem solving with C++ (6th ed.). Burlington, MA: Jones & Bartlett Learning. ISBN978-1449694289. OCLC 894992484.
- ^ Dr. Dobb'south Sourcebook. United states of americaA.: Miller Freeman, Inc. Nov–December 1995.
- ^ "Using C for CGI Programming". linuxjournal.com. March 1, 2005. Archived from the original on February thirteen, 2010. Retrieved January 4, 2010.
- ^ McMillan, Robert (Baronial 1, 2013). "Is Java Losing Its Mojo?". Wired. Archived from the original on February 15, 2017. Retrieved March 5, 2017.
- ^ O'Regan, Gerard (September 24, 2015). Pillars of calculating : a compendium of select, pivotal applied science firms. ISBN978-3319214641. OCLC 922324121.
- ^ Rauchwerger, Lawrence (2004). Languages and compilers for parallel computing : 16th international workshop, LCPC 2003, College Station, TX, U.s.a., October 2-iv, 2003 : revised papers. Springer. ISBN978-3540246442. OCLC 57965544.
- ^ Stroustrup, Bjarne (1993). "A History of C++: 1979−1991" (PDF). Archived (PDF) from the original on February 2, 2019. Retrieved June ix, 2011.
Sources [edit]
- Ritchie, Dennis K. (March 1993). "The Evolution of the C Linguistic communication". ACM SIGPLAN Notices. ACM. 28 (3): 201–208. doi:10.1145/155360.155580.
Ritchie, Dennis M. (1993). "The Development of the C Language". The Second ACM SIGPLAN Briefing on History of Programming Languages (HOPL-II). ACM. pp. 201–208. doi:ten.1145/154766.155580. ISBN0-89791-570-4 . Retrieved Nov 4, 2014. - Kernighan, Brian Westward.; Ritchie, Dennis Thou. (1996). The C Programming Linguistic communication (2nd ed.). Prentice Hall. ISBN7-302-02412-10.
Further reading [edit]
- Kernighan, Brian; Ritchie, Dennis (1988). The C Programming Language (two ed.). Prentice Hall. ISBN978-0131103627. (annal)
- Plauger, P.J. (1992). The Standard C Library (ane ed.). Prentice Hall. ISBN978-0131315099. (source)
- Banahan, M.; Brady, D.; Doran, Chiliad. (1991). The C Book: Featuring the ANSI C Standard (2 ed.). Addison-Wesley. ISBN978-0201544336. (free)
- Harbison, Samuel; Steele Jr, Guy (2002). C: A Reference Manual (5 ed.). Pearson. ISBN978-0130895929. (archive)
- King, K.N. (2008). C Programming: A Modernistic Approach (2 ed.). W. Due west. Norton. ISBN978-0393979503. (archive)
- Griffiths, David; Griffiths, Dawn (2012). Caput Outset C (1 ed.). O'Reilly. ISBN978-1449399917.
- Perry, Greg; Miller, Dean (2013). C Programming: Accented Beginner'southward Guide (iii ed.). Que. ISBN978-0789751980.
- Deitel, Paul; Deitel, Harvey (2015). C: How to Plan (eight ed.). Pearson. ISBN978-0133976892.
- Gustedt, Jens (2019). Modern C (2 ed.). Manning. ISBN978-1617295812. (complimentary)
External links [edit]
- ISO C Working Group official website
- ISO/IEC 9899, publicly available official C documents, including the C99 Rationale
- "C99 with Technical corrigenda TC1, TC2, and TC3 included" (PDF). (three.61 MB)
- comp.lang.c Frequently Asked Questions
- A History of C, by Dennis Ritchie
Source: https://en.wikipedia.org/wiki/C_(programming_language)
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