C(7) BSD Miscellaneous Information Manual C(7)NAME
c, c78, c89, c90, c99 — The C programming language
DESCRIPTION
C is a general purpose programming language, which has a strong connec‐
tion with the UNIX operating system and its derivatives, since the vast
majority of those systems were written in the C language. The C language
contains some basic ideas from the BCPL language through the B language
written by Ken Thompson in 1970 for the DEC PDP-7 machines. The develop‐
ment of the UNIX operating system was started on a PDP-7 machine in
assembly language, but this choice made it very difficult to port the
existing code to other systems.
In 1972 Dennis M. Ritchie worked out the C programming language for fur‐
ther development of the UNIX operating system. The idea was to implement
only the C compiler for different platforms, and implement most parts of
the operating system in the new programming language to simplify the
portability between different architectures. It follows that C is very
well adapted for (but not limited to) writing operating systems and low-
level applications.
The C language did not have a specification or standardized version for a
long time. It went through a lot of changes and improvements for ages.
In 1978, Brian W. Kernighan and Dennis M. Ritchie published the first
book about C under the title “The C Programming Language”. We can think
of this book as the first specification of the language. This version is
often referred to as “K&R C” after the names of the authors. Sometimes
it is referred to as C78, as well, after the publishing year of the first
edition of the book.
It is important to notice that the instruction set of the language is
limited to the most fundamental elements for simplicity. Handling of the
standard I/O and similar common functions are implemented in the
libraries shipped with the compiler. As these functions are also widely
used, it was demanded to include into the description what requisites the
library should conform to, not just strictly the language itself.
Accordingly, the aforementioned standards cover the library elements, as
well. The elements of this standard library are still not enough for
more complicated tasks. In this case the provided system calls of the
given operating system can be used. To not lose the portability by using
these system calls, the POSIX (Portable Operating System Interface (for
Unix)) standard evolved. It describes what functions should be available
to keep portability. Note, that POSIX is not a C standard, but an oper‐
ating system standard and thus is beyond the scope of this manual. The
standards discussed below are all C standards and only cover the C pro‐
gramming language and the accompanying library.
After the publication of the book mentioned before, the American National
Standards Institute (ANSI) started to work on standardizing the language,
and in 1989 they announced ANSI X3.159-1989. It is usually referred to
as ANSI C or C89. The main difference in this standard were the function
prototypes, which was a new way of declaring functions. With the old-
style function declarations, the compiler was unable to check the sanity
of the actual parameters of a function call. The old syntax was highly
error-prone because incompatible parameters were hard to detect in the
program code and the problem only showed up at run-time.
In 1990, the International Organization for Standardization (ISO) adopted
the ANSI standard as ISO/IEC 9899:1990. This is also referred to as ISO
C or C90. It only contains negligible minor modifications against ANSI
C, so the two standards are often considered to be fully equivalent.
This was a very important milestone in the history of the C language, but
the development of the language did not stop.
The ISO C standard was later extended with an amendment as ISO/IEC 9899
AM1 in 1995. This contained, for example, the wide-character support in
wchar.h and wctype.h. Two corrigenda were also published: Technical Cor‐
rigendum 1 as ISO/IEC 9899 TCOR1 in 1995 and Technical Corrigendum 2 as
ISO/IEC 9899 TCOR2 in 1996. The continuous development and growth made
it necessary to work out a new standard, which contains the new features
and fixes the known defects and deficiencies of the language. As a
result, ISO/IEC 9899:1999 was born in 1999. Similarly to the other stan‐
dards, this is referred to after the publication year as C99. The
improvements include the following:
· Inline functions.
· Support for variable length arrays.
· New high-precision integer type named long long int, and other
integer types described in stdint(3) and inttypes(3).
· New boolean data type; see stdbool(3).
· One line comments taken from the C++ language.
· Some new preprocessor features.
· A predefined identifier __func__ and a restrict type qualifier.
· New variables can be declared anywhere, not just in the begin‐
ning of the program or program blocks.
· No implicit int type.
Since then no new standards have been published, but the C language is
still evolving. New and useful features have been showing up in the most
famous C compiler: GNU C (gcc(1)). Most of the UNIX-like operating sys‐
tems use GNU C as a system compiler, but the various extensions of GNU C,
such as attribute(3) or typeof(3), should not be considered standard fea‐
tures.
SEE ALSOc89(1), c99(1), cc(1), cdefs(3)
Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language,
Prentice Hall, Second Edition, 40th printing, 1988.
STANDARDS
ANSI, X3.159-1989.
ISO/IEC, 9899:1990, Programming languages -- C.
ISO/IEC, 9899 AM1.
ISO/IEC, 9899 TCOR1, Programming languages -- C, Technical Corrigendum 1.
ISO/IEC, 9899 TCOR2, Programming languages -- C, Technical Corrigendum 2.
ISO/IEC, 9899:1999, Programming languages -- C.
ISO/IEC, 9899:1999 TCOR1, Programming languages -- C, Technical
Corrigendum 1.
ISO/IEC, 9899:1999 TCOR2, Programming languages -- C, Technical
Corrigendum 2.
ISO/IEC, 9899:1999 TCOR3, Programming languages -- C, Technical
Corrigendum 3.
HISTORY
This manual page first appeared in FreeBSD 9.0 and NetBSD 6.0.
AUTHORS
This manual page was written by Gabor Kovesdan ⟨gabor@FreeBSD.org⟩.
BSD March 30, 2011 BSD
