cdecl
CDECL(1) Linux Programmer’s Manual CDECL(1)
NAME
cdecl, c++decl - Compose C and C++ type declarations
SYNOPSIS
cdecl [-a | -+ | -p | -r] [-ciqdDV]
[[ files ...] | explain ... | declare ... | cast ... | set ... |
help | ? ]
c++decl [-a | -+ | -p | -r] [-ciqdDV]
[[ files ...] | explain ... | declare ... | cast ... | set ... |
help | ? ]
explain ...
declare ...
cast ...
DESCRIPTION
Cdecl (and c++decl) is a program for encoding and decoding C (or C++)
type declarations. The C language is based on the (draft proposed)
X3J11 ANSI Standard; optionally, the C language may be based on the
pre-ANSI definition defined by Kernighan & Ritchie’s The C Programming
Language book, or the C language defined by the Ritchie PDP-11 C com-
piler. The C++ language is based on Bjarne Stroustrup’s The C++ Pro-
gramming Language, plus the version 2.0 additions to the language.
OPTIONS
-a Use the ANSI C dialect of the C language.
-p Use the pre-ANSI dialect defined by Kernighan & Ritchie’s book.
-r Use the dialect defined by the Ritchie PDP-11 C compiler.
-+ Use the C++ language, rather than C.
-i Run in interactive mode (the default when reading from a termi-
nal). This also turns on prompting, line editing, and line
history.
-q Quiet the prompt. Turns off the prompt in interactive mode.
-c Create compilable C or C++ code as output. Cdecl will add a
semicolon to the end of a declaration and a pair of curly
braces to the end of a function definition.
-d Turn on debugging information (if compiled in).
-D Turn on YACC debugging information (if compiled in).
-V Display version information and exit.
INVOKING
Cdecl may be invoked under a number of different names (by either
renaming the executable, or creating a symlink or hard link to it).
If it is invoked as cdecl then ANSI C is the default language. If it
is invoked as c++decl then C++ is the default. If it is invoked as
either explain, cast, or declare then it will interpret the rest of
the command line options as parameters to that command, execute the
command, and exit. It will also do this if the first non-switch argu-
ment on the command line is one of those three commands. Input may
also come from a file.
Cdecl reads the named files for statements in the language described
below. A transformation is made from that language to C (C++) or
pseudo-English. The results of this transformation are written on
standard output. If no files are named, or a filename of ‘‘-’’ is
encountered, standard input will be read. If standard input is coming
from a terminal, (or the -i option is used), a prompt will be written
to the terminal before each line. The prompt can be turned off by the
-q option (or the set noprompt command). If cdecl is invoked as
explain, declare or cast, or the first argument is one of the commands
discussed below, the argument list will be interpreted according to
the grammar shown below instead of as file names.
When it is run interactively, cdecl uses the GNU readline library to
provide keyword completion and command line history, very much like
bash(1) (q.v.). Pressing TAB will complete the partial keyword before
the cursor, unless there is more than one possible completion, in
which case a second TAB will show the list of possible completions and
redisplay the command line. The left and right arrow keys and
backspace can be used for editing in a natural way, and the up and
down arrow keys retrieve previous command lines from the history.
Most other familiar keys, such as Ctrl-U to delete all text from the
cursor back to the beginning of the line, work as expected. There is
an ambiguity between the int and into keywords, but cdecl will guess
which one you meant, and it always guesses correctly.
You can use cdecl as you create a C program with an editor like vi(1)
or emacs(1). You simply type in the pseudo-English version of the
declaration and apply cdecl as a filter to the line. (In vi(1), type
‘‘!!cdecl<cr>’’.)
If the create program option -c is used, the output will include semi-
colons after variable declarations and curly brace pairs after func-
tion declarations.
The -V option will print out the version numbers of the files used to
create the process. If the source is compiled with debugging informa-
tion turned on, the -d option will enable it to be output. If the
source is compiled with YACC debugging information turned on, the -D
option will enable it to be output.
COMMAND LANGUAGE
There are six statements in the language. The declare statement com-
poses a C type declaration from a verbose description. The cast
statement composes a C type cast as might appear in an expression.
The explain statement decodes a C type declaration or cast, producing
a verbose description. The help (or ?) statement provides a help
message. The quit (or exit) statement (or the end of file) exits the
program. The set statement allows the command line options to be set
interactively. Each statement is separated by a semi-colon or a new-
line.
SYNONYMS
Some synonyms are permitted during a declaration:
character is a synonym for char
constant is a synonym for const
enumeration is a synonym for enum
func is a synonym for function
integer is a synonym for int
ptr is a synonym for pointer
ref is a synonym for reference
ret is a synonym for returning
structure is a synonym for struct
vector is a synonym for array
The TAB completion feature only knows about the keywords in the right
column of the structure, not the ones in the left column. TAB comple-
tion is a lot less useful when the leading characters of different
keywords are the same (the keywords confict with one another), and
putting both columns in would cause quite a few conflicts.
GRAMMAR
The following grammar describes the language. In the grammar, words
in "<>" are non-terminals, bare lower-case words are terminals that
stand for themselves. Bare upper-case words are other lexical tokens:
NOTHING means the empty string; NAME means a C identifier; NUMBER
means a string of decimal digits; and NL means the new-line or semi-
colon characters.
<program> ::= NOTHING
| <program> <stmt> NL
<stmt> ::= NOTHING
| declare NAME as <adecl>
| declare <adecl>
| cast NAME into <adecl>
| cast <adecl>
| explain <optstorage> <ptrmodlist> <type> <cdecl>
| explain <storage> <ptrmodlist> <cdecl>
| explain ( <ptrmodlist> <type> <cast> ) optional-NAME
| set <options>
| help | ?
| quit
| exit
<adecl> ::= array of <adecl>
| array NUMBER of <adecl>
| function returning <adecl>
| function ( <adecl-list> ) returning <adecl>
| <ptrmodlist> pointer to <adecl>
| <ptrmodlist> pointer to member of class NAME <adecl>
| <ptrmodlist> reference to <adecl>
| <ptrmodlist> <type>
<cdecl> ::= <cdecl1>
| * <ptrmodlist> <cdecl>
| NAME :: * <cdecl>
| & <ptrmodlist> <cdecl>
<cdecl1> ::= <cdecl1> ( )
| <cdecl1> ( <castlist> )
| <cdecl1> [ ]
| <cdecl1> [ NUMBER ]
| ( <cdecl> )
| NAME
<cast> ::= NOTHING
| ( )
| ( <cast> ) ( )
| ( <cast> ) ( <castlist> )
| ( <cast> )
| NAME :: * <cast>
| * <cast>
| & <cast>
| <cast> [ ]
| <cast> [ NUMBER ]
<type> ::= <typename> | <modlist>
| <modlist> <typename>
| struct NAME | union NAME | enum NAME | class NAME
<castlist> ::= <castlist> , <castlist>
| <ptrmodlist> <type> <cast>
| <name>
<adecllist> ::= <adecllist> , <adecllist>
| NOTHING
| <name>
| <adecl>
| <name> as <adecl>
<typename> ::= int | char | double | float | void
<modlist> ::= <modifier> | <modlist> <modifier>
<modifier> ::= short | long | unsigned | signed | <ptrmod>
<ptrmodlist> ::= <ptrmod> <ptrmodlist> | NOTHING
<ptrmod> ::= const | volatile | noalias
<storage> ::= auto | extern | register | auto
<optstorage> ::= NOTHING | <storage>
<options> ::= NOTHING | <options>
| create | nocreate
| prompt | noprompt
| ritchie | preansi | ansi | cplusplus
| debug | nodebug | yydebug | noyydebug
SET OPTIONS
The set command takes several options. You can type set or set
options to see the currently selected options and a summary of the
options which are available. The first four correspond to the -a, -p,
-r, and -+ command line options, respectively.
ansi Use the ANSI C dialect of the C language.
preansi
Use the pre-ANSI dialect defined by Kernighan & Ritchie’s book.
ritchie
Use the dialect defined by the Ritchie PDP-11 C compiler.
cplusplus
Use the C++ language, rather than C.
[no]prompt
Turn on or off the prompt in interactive mode.
[no]create
Turn on or off the appending of semicolon or curly braces to
the declarations output by cdecl. This corresponds to the -c
command line option.
[no]debug
Turn on or off debugging information.
[no]yydebug
Turn on or off YACC debugging information.
Note: debugging information and YACC debugging information are only
available if they have been compiled into cdecl. The last two options
correspond to the -d and -D command line options, respectively.
Debugging information is normally used in program development, and is
not generally compiled into distributed executables.
EXAMPLES
To declare an array of pointers to functions that are like malloc(3),
do
declare fptab as array of pointer to function returning pointer
to char
The result of this command is
char *(*fptab[])()
When you see this declaration in someone else’s code, you can make
sense out of it by doing
explain char *(*fptab[])()
The proper declaration for signal(2), ignoring function prototypes, is
easily described in cdecl’s language:
declare signal as function returning pointer to function
returning void
which produces
void (*signal())()
The function declaration that results has two sets of empty parenthe-
ses. The author of such a function might wonder where to put the
parameters:
declare signal as function (arg1,arg2) returning pointer to
function returning void
provides the following solution (when run with the -c option):
void (*signal(arg1,arg2))() { }
If we want to add in the function prototypes, the function prototype
for a function such as _exit(2) would be declared with:
declare _exit as function (retvalue as int) returning void
giving
void _exit(int retvalue) { }
As a more complex example using function prototypes, signal(2) could
be fully defined as:
declare signal as function(x as int, y as pointer to func-
tion(int) returning void) returning pointer to function(int)
returning void
giving (with -c)
void (*signal(int x, void (*y)(int )))(int ) { }
Cdecl can help figure out the where to put the "const" and "volatile"
modifiers in declarations, thus
declare foo as pointer to const int
gives
const int *foo
while
declare foo as const pointer to int
gives
int * const foo
C++decl can help with declaring references, thus
declare x as reference to pointer to character
gives
char *&x
C++decl can help with pointers to member of classes, thus declaring a
pointer to an integer member of a class X with
declare foo as pointer to member of class X int
gives
int X::*foo
and
declare foo as pointer to member of class X function (arg1,
arg2) returning pointer to class Y
gives
class Y *(X::*foo)(arg1, arg2)
DIAGNOSTICS
The declare, cast and explain statements try to point out construc-
tions that are not supported in C. In some cases, a guess is made as
to what was really intended. In these cases, the C result is a toy
declaration whose semantics will work only in Algol-68. The list of
unsupported C constructs is dependent on which version of the C lan-
guage is being used (see the ANSI, pre-ANSI, and Ritchie options).
The set of supported C++ constructs is a superset of the ANSI set,
with the exception of the noalias keyword.
REFERENCES
ANSI Standard X3.159-1989 (ANSI C)
ISO/IEC 9899:1990 (the ISO standard)
The comp.lang.c FAQ
http://www.eskimo.com/~scs/C-faq.top.html
Section 8.4 of the C Reference Manual within The C Programming Lan-
guage by B. Kernighan & D. Ritchie.
Section 8 of the C++ Reference Manual within The C++ Programming Lan-
guage by B. Stroustrup.
CAVEATS
The pseudo-English syntax is excessively verbose.
There is a wealth of semantic checking that isn’t being done.
Cdecl was written before the ANSI C standard was completed, and no
attempt has been made to bring it up-to-date. Nevertheless, it is
very close to the standard, with the obvious exception of noalias.
Cdecl’s scope is intentionally small. It doesn’t help you figure out
initializations. It expects storage classes to be at the beginning of
a declaration, followed by the the const, volatile and noalias modi-
fiers, followed by the type of the variable. Cdecl doesn’t know any-
thing about variable length argument lists. (This includes the
‘‘,...’’ syntax.)
Cdecl thinks all the declarations you utter are going to be used as
external definitions. Some declaration contexts in C allow more flex-
ibility than this. An example of this is:
declare argv as array of array of char
where cdecl responds with
Warning: Unsupported in C -- ’Inner array of unspecified size’
(maybe you mean "array of pointer")
char argv[][]
Tentative support for the noalias keyword was put in because it was in
the draft ANSI specifications.
AUTHORS
Originally written by Graham Ross, improved and expanded by David
Wolverton, Tony Hansen, and Merlyn LeRoy.
GNU readline support and Linux port by David R. Conrad, <con-
rad@detroit.freenet.org>
SEE ALSO
bash(1), emacs(1), malloc(3), vi(1).
Version 2.5 15 January 1996 CDECL(1)
