--- name: "c++decl" section: "1" platform: "linux" package: "cdecl" version: "2.5-15+b1" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/cdecl" --- # c++decl(1) Compose C and C++ type declarations Part of [cdecl(1)](/cdecl/1.md). ## 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 compiler. The C++ language is based on Bjarne Stroustrup's *The C++ Programming 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 terminal). 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 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)](/bash/1.md) (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)](/vi/1.md) or [*emacs*(1)](/emacs/1.md). You simply type in the pseudo-English version of the declaration and apply *cdecl* as a filter to the line. (In [*vi*(1)](/vi/1.md), type \`\`**!!cdecl**\''.) 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 information 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 composes 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 newline. ## 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 completion 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. ``` ::= NOTHING | NL ::= NOTHING | declare NAME as | declare | cast NAME into | cast | explain | explain | explain ( ) optional-NAME | set | help | ? | quit | exit ::= array of | array NUMBER of | function returning | function ( ) returning | pointer to | pointer to member of class NAME | reference to | ::= | * | NAME :: * | & ::= ( ) | ( ) | [ ] | [ NUMBER ] | ( ) | NAME ::= NOTHING | ( ) | ( ) ( ) | ( ) ( ) | ( ) | NAME :: * | * | & | [ ] | [ NUMBER ] ::= | | | struct NAME | union NAME | enum NAME | class NAME ::= , | | ::= , | NOTHING | | | as ::= int | char | double | float | void ::= | ::= short | long | unsigned | signed | ::= | NOTHING ::= const | volatile | noalias ::= auto | extern | register | static ::= NOTHING | ::= NOTHING | | 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)](/malloc/3.md), 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)](/signal/2.md), 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 parentheses. 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)](/_exit/2.md) 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)](/signal/2.md) could be fully defined as: declare signal as function(x as int, y as pointer to function(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 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 Language* by B. Kernighan & D. Ritchie. Section 8 of the C++ Reference Manual within *The C++ Programming Language* 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 modifiers, followed by the type of the variable. *Cdecl* doesn't know anything 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 flexibility 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, \ ## SEE ALSO [*bash*(1)](/bash/1.md), [*emacs*(1)](/emacs/1.md), [*malloc*(3)](/malloc/3.md), [*vi*(1)](/vi/1.md).