NAME
c, c78, c89, c90, c99 —
The C
programming language
DESCRIPTION
C is a general purpose programming language, which has a strong connection 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 development 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 further
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 operating
system standard and thus is beyond the scope of this manual. The standards
discussed below are all C standards and only cover the C programming 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 Corrigendum 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 standards, 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
beginning 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 systems 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 features.
SEE ALSO
c89(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>.