184 lines
7.0 KiB
Groff
184 lines
7.0 KiB
Groff
.\" Copyright (C) 2007, 2010 Gabor Kovesdan. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd May 30, 2011
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.Dt C 7
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.Os
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.Sh NAME
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.Nm c, c78, c89, c90, c99
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.Nd The C programming language
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.Sh DESCRIPTION
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C is a general purpose programming language, which has a strong connection
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with the UNIX operating system and its derivatives, since the vast
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majority of those systems were written in the C language.
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The C language contains some basic ideas from the BCPL language through
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the B language written by Ken Thompson in 1970 for the DEC PDP-7 machines.
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The development of the UNIX operating system was started on a PDP-7
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machine in assembly language, but it made very difficult to port the existing
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code to other systems.
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.Pp
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In 1972 Dennis M. Ritchie worked out the C programming language for
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further development of the UNIX operating system.
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The idea was to implement only the C compiler for different
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platforms, and implement most part of the operating system
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in the new programming language to simplify the portability between
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different architectures.
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It follows that C is very eligible for (but not limited to) writing
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operating systems and low-level applications.
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.Pp
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The C language did not have a specification or standardized version for
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a long time.
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It went through a lot of changes and improvements for ages.
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In 1978, Brian W. Kernighan and Dennis M. Ritchie published the
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first book about C under the title "The C Programming Language".
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We can think of this book as the first specification of the language.
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This version is often referred as K&R C after the names of the authors.
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Sometimes it is referred as C78, as well, after the publishing year of
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the first edition of the book.
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.Pp
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It is important to notice, that the instruction set of the language is
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limited to the most fundamental elements for simplicity.
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Handling of the standard I/O and such common functions are implemented in
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the libraries shipped with the compiler.
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As these functions are also widely used, it was demanded to include into
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the description what requisites the library should conform to, not just
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strictly the language itself.
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Accordingly, the aforementioned standards cover the library elements, as well.
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The elements of this standard library is still not enough for more
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complicated tasks.
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In this case the provided system calls of the given operating system can be
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used.
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To not loose the portability by using these system calls, the POSIX
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(Portable Operating System Interface) standard evolved.
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It describes what functions should be available to keep portability.
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Note, that POSIX is not a C standard, but an operating system standard
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and thus is beyond the scope of this manual.
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The standards discussed below are all C standards and only cover
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the C programming language and the accompanying library.
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.Pp
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After the publication of the book mentioned before,
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the American National Standards Institute (ANSI) started to work on
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standardizing the language, and they announced ANSI X3.159-1989
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in 1989.
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It is usually referred as ANSI C or C89.
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The main difference in this standard were the function prototypes,
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which is a new way of declaring functions.
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With the old-style function declarations, the compiler was unable to
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check the sanity of the actual parameters at a function call.
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The old syntax was highly error-prone because incompatible parameters
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were hard to detect in the program code and the problem only showed up
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at run-time.
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.Pp
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In 1990, the International Organization for Standardization (ISO) adopted
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the ANSI standard as ISO/IEC 9899:1990 in 1990.
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This is also referred as ISO C or C90.
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It only contains negligible minor modifications against ANSI C,
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so the two standards often considered to be fully equivalent.
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This was a very important milestone in the history of the C language, but the
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development of the language did not stop.
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.Pp
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The ISO C standard was later extended with an amendment as
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ISO/IEC 9899 AM1 in 1995.
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This contained, for example, the wide-character support in wchar.h and
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wctype.h.
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Two corrigenda were also published: Technical Corrigendum 1 as
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ISO/IEC 9899 TCOR1 in 1995 and Technical Corrigendum 2 as ISO/IEC 9899 TCOR1
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in 1996.
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The continuous development and growth made it necessary to work out a new
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standard, which contains the new features and fixes the known defects and
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deficiencies of the language.
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As a result, ISO/IEC 9899:1999 was born in 1999.
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Similarly to the other standards, this is referred after the
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publication year as C99.
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The improvements include the following:
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.Bl -bullet -offset indent
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.It
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Inline functions
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.It
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Support for variable length arrays
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.It
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New high-precision integer type named long long int, and other integer types
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defined in stdint.h
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.It
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New boolean data type implemented in stdbool.h
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.It
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One line comments taken from the C++ language
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.It
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Some new preprocessor features
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.It
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New variables can be declared anywhere, not just in the beginning of the
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program or program blocks
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.It
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No implicit int type
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.El
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.Pp
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Since then new standards have not been published, but the C language is still
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evolving.
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New and useful features have been showed up in the most famous
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C compiler: GNU C.
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Most of the UNIX-like operating systems use GNU C as a system compiler,
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but those addition in GNU C should not be considered as
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standard features.
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.Sh SEE ALSO
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.Xr cc 1 ,
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.Xr c89 1 ,
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.Xr c99 1
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.Sh STANDARDS
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.Rs
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.%A ANSI
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.%T X3.159-1989
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1990, Programming languages -- C
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899 AM1
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899 TCOR1, Programming languages -- C, Technical Corrigendum 1
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899 TCOR2, Programming languages -- C, Technical Corrigendum 2
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1999, Programming languages -- C
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.Re
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.Sh HISTORY
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This manual page first appeared in
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.Fx 9.0 .
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.Sh AUTHORS
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This manual page was originally written by
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.An Gabor Kovesdan Aq gabor@FreeBSD.org .
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