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 his-
              tory.

       -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  com-
       mand  line  options as parameters to that command, execute the command,
       and exit.  It will also do this if the first non-switch argument 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 redis-
       play 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 dec-
       laration  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 function
       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 state-
       ment 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  mes-
       sage.  The quit (or exit) statement (or the end of file) exits the pro-
       gram.  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 key-
       words 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:  NOTH-
       ING  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 char-
       acters.

            <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  com-
              mand 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.  Debug-
       ging 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 return-
              ing 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 constructions
       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  language  is  being
       used  (see  the  ANSI, pre-ANSI, and Ritchie options).  The set of sup-
       ported 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 Language
       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 flexi-
       bility 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)

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