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C2MAN(1) FreeBSD General Commands Manual C2MAN(1)

c2man - generate manual pages from C source code

c2man [ option ... ] [ file ... ]

c2man reads C source code files in which comments have been strategically placed, and outputs manual page(s) documenting each function defined or declared (via a prototype), and optionally each variable with global scope. Function definitions and declarations may be in the old style or ISO/ANSI style. If no file argument is given, c2man takes its input from the standard input.

If a .h file is written as a formal interface description when preparing an interface spec, c2man can generate all the manual pages required for the spec at one fell swoop, and then keep them up to date automatically as the interface changes.

Since c2man will accept either function definitions or prototypes, it can be used on either .c or .h files. If the input is a header file, any files specified by -i options are assumed to be prerequisites, and get parsed before the input file. (Any file whose extension begins with ``h'', matched case-insensitively, is considered a header file.)

This is potentially a huge win for most programmers that just love documenting their functions, and updating the documentation every time it changes. Here's an example, named example.h:

enum Place
    HOME,      /* Home, Sweet Home */
    WORK,      /* where I spend lots of time */
    MOVIES,    /* Saturday nights mainly */
    CITY,      /* New York, New York */
    COUNTRY    /* Bob's Country Bunker */
 * do some useful work for a change.
 * This function will actually get some productive
 * work done, if you are really lucky.
 * returns the number of milliseconds in a second.
int dowork(int count,        /* how much work to do */
           enum Place where, /* where to do the work */
           long fiveoclock   /* when to knock off */);


% c2man example.h

is run, this produces a file named dowork.3 which can be processed by man(1) or used as:

% nroff -man dowork.3

to produce:

dowork - do some useful work for a change.

#include <example.h>

int dowork
int count,
enum Place where,
long fiveoclock

int count
How much work to do.
enum Place where
Where to do the work.

Possible values for an enum Place are as follows:

Home, Sweet Home.
Where I spend lots of time.
Saturday nights mainly.
New York, New York.
Bob's Country Bunker.
long fiveoclock
When to knock off.

This function will actually get some productive work done, if you are really lucky.

The number of milliseconds in a second.

By default, a separate output file is generated for each global identifier (i.e. function or variable) documented by c2man.

Much of c2man's information is extracted from the comment placed immediately before the declaration/definition of the identifier being documented; this comment is taken to describe the identifier and must be present, or the identifier will be ignored entirely. In the case of a variable declaration/definition, this comment may instead be placed after it starting on the same line.

Global variables are not documented, unless the -v option is used.

Identifiers declared static are ignored by default unless the file is a header file (which is most useful with inline functions) or the -s option is used.

Declarations with the extern keyword are ignored unless they appear in a header file; note that this does not include function definitions.

Each manual page starts with a NAME section, listing the name(s) of the identifier(s) documented, along with a terse description. By default, this description is the first line or sentence of the comment describing the identifier. With the -g option, it is found after the first dash (-) in the first comment of the file, and the -G option specifies it explicitly.

The SYNOPSIS section begins with an #include line if the source file is a header. After this is an external declaration for the identifier(s) being documented.

Information in the PARAMETERS section is gleaned from the comments immediately before or after each parameter declaration. A comment after a parameter can follow the comma that separates that parameter from the next, if the comment starts on the same line and is the only remaining thing on that line. Leading underscores in a parameter name are stripped when printed in the manual page.

If the manual page is for a group of functions (i.e. -g or -G options), identical parameters (in both name and type) common to more than one function are described only once if only one has a comment (as in the ctype example below).

If a parameter is an enumerated type, all the possible values it can take are output, along with their descriptions. These descriptions are gleaned from the comments surrounding the enum identifiers where the type was defined. Comments describing enum identifiers are placed in a similar manner to those that describe function parameters. enum identifiers that begin with an underscore are ignored, which is useful for padding or _NUMBER_OF_... values which aren't normally used by someone calling the function. If none of the identifiers in an enumerated type has a comment, c2man will bunch them together to save space.

The DESCRIPTION section contains everything after the first line or sentence of the comment describing the identifier, up until the word ``returns'' at the start of a line, matched case-insensitively and optionally followed by a colon (:). In the case of a variable of enumerated type, it will also list all the values it can hold.

The RETURNS section contains anything after that. Any of these lines that begin with a single word followed by a colon or a tab generate tagged paragraphs so that lists of possible return values and error codes look neat. If the function is void, don't put anything like "Returns: nothing" in the comment, since it's a waste of space. If the identifier is a function returning an enumerated type, its possible values will be listed here.

The RETURNS section is also added if there is a comment after the function return type.

5 For example: /* Sample function */
char *			/* NULL if failed string otherwise */

The RETURNS section will contain the full contents of the comment (stripping the optional leading asterisk). It is not possible to use both methods to specify a description for the return value. In that case the comment after the return type supersedes whatever was specified for the return value in the comment above the function.

Finally, a SEE ALSO section is generated, referencing all the other manual pages generated, if any.

The RETURNS, PARAMETERS and SEE ALSO sections are omitted entirely if they aren't needed.

Both C and C++ style comments are recognized, with separate consecutive single-line comments coalesced into a single block. When looking at comments, c2man ignores everything before the first alpha-numeric character. After that, it ignores leading white-space, leading asterisks and leading slashes on all subsequent lines, and ignores all trailing lines thus rendered blank. If that leaves nothing, the comment is ignored entirely. This makes it very flexible in supporting popular comment boxing.

Comments can be placed with considerable flexibility so that most commenting styles are supported.

13 The following variations of the enum definition in the dowork.h example are all equivalent: /* commas after the comments. */
enum Place
    HOME       /* Home, Sweet Home */,
    WORK       /* where I spend lots of time */,
    MOVIES     /* Saturday nights mainly */,
    CITY       /* New York, New York */,
    COUNTRY    /* Bob's Country Bunker */

16 /* the comment needn't go on the same line,
 * if the comma goes after the comment.
enum Place
    	/* Home, Sweet Home */,
    	/* where I spend lots of time */,
    	/* Saturday nights mainly */,
    	/* New York, New York */,
    	/* Bob's Country Bunker */

14 /* the comment can go before it too. */
enum Place
    /* Home, Sweet Home */
    /* where I spend lots of time */
    /* Saturday nights mainly */
    /* New York, New York */
    /* Bob's Country Bunker */

But the following example is NOT equivalent because the commas are between the identifier and the its associated comment, and the comment is on a different line. Each comment actually applies to the wrong identifier, so this will result in very misleading output.
16 Don't do this: enum Place
    	/* Home, Sweet Home */
    	/* where I spend lots of time */
    	/* Saturday nights mainly */
    	/* New York, New York */
    	/* Bob's Country Bunker */

Since enum identifiers sometimes fall into logical groups, a comment before such an identifier will be taken to apply to the next few in the list, provided that the comments describing each individual identifier are placed after them. Also, there must be a blank line separating the comment describing the next logical group and the comment at the end of the previous line, or the two will be coalesced and incorrectly treated as a single comment for the previous enumerator.

17 In other words, you can go: /* include logical grouping comments. */
enum Place
    /* These take up most of the week */
    HOME,      /* Home, Sweet Home */
    WORK,      /* where I spend lots of time */
    /* More for special occasions */
    MOVIES,     /* Saturday nights mainly */
    CITY,      /* New York, New York */
    /* The real favourite */
    COUNTRY    /* Bob's Country Bunker */

That may all sound a bit complex, but the upshot is that c2man will usually know which identifier a comment is associated with, unless you do something truly bizarre.

Basic punctuation and capitalisation corrections are made in each section for neatness, and the typesetting program used to process the output will generally reformat line breaks according to the width of the output device. Blank lines in a comment will be preserved, and lines starting with a dash (-), an asterisk (*), or a numbered point ((n), n) or n.), will cause a line break, allowing simple bulleted or numbered lists.

Lines beginning with a tab after the comment leader will be output verbatim without reformatting, to allow source code to be embedded in the comments.

Typesetter specific commands may be included for more complex processing, although this isn't recommended since it ties you to a particular typesetter.

Simple, closely related objects can be grouped together onto a single page with the -g or -G options. By default, this results in a single output file with multiple links so that it can be accessed by the name of the input file, or of any identifier documented. For example, if ctype.h contains:

/* ctype.h - character classification functions */
/* character is alphanumeric
 * returns 0 if the character doesn't fit the
 * classification; non-zero (but not necessarily 1)
 * if it does.
inline int isalnum(int c	/* the character to classify */);
/* character is a letter */
inline int isalpha(int c);
/* character is a control character */
inline int iscntrl(int c);
/* character is a digit */
inline int isdigit(int c);
/* character is a graphic */
inline int isgraph(int c);
/* character is a lower case letter */
inline int islower(int c);
/* character is printable */
inline int isprint(int c);
/* character is punctuation */
inline int ispunct(int c);
/* character is a a form of whitespace */
inline int isspace(int c);
/* character is an upper case letter */
inline int isupper(int c);
/* character is a hexadecimal digit */
inline int isxdigit(int c);

then using:

% c2man -g ctype.h


isalnum, isalpha, iscntrl, isdigit, isgraph, islower, isprint, ispunct, isspace, isupper, isxdigit - character classification functions

#include <ctype.h>

inline int isalnum(int c);

inline int isalpha(int c);

inline int iscntrl(int c);

inline int isdigit(int c);

inline int isgraph(int c);

inline int islower(int c);

inline int isprint(int c);

inline int ispunct(int c);

inline int isspace(int c);

inline int isupper(int c);

inline int isxdigit(int c);

int c
The character to classify.

Character is alphanumeric.

Character is a letter.

Character is a control character.

Character is a digit.

Character is a graphic.

Character is a lower case letter.

Character is printable.

Character is punctuation.

Character is a a form of whitespace.

Character is an upper case letter.

Character is a hexadecimal digit.

0 if the character doesn't fit the classification; non-zero (but not necessarily 1) if it does.

Additional sections not otherwise recognized by c2man can be included in the manual page by including them in the comment describing the identifier. A section heading is preceded in the comment by an empty line (after removal of leading asterisks), and is the only word on it's line, or is a word followed by a colon (:), or is a line ending with a colon, so section names with spaces are allowed, like "Return value:".

Section heading names are capitalized, and the names DESCRIPTION, RETURNS and NAME are recognized specially so you can name them explicitly if you like. FUNCTION, PROCEDURE and ROUTINE are also recognised, and treated identically to NAME.

9 For example: /*
 * Have a quick puff.
 * Warning: Smoking causes lung cancer
void go_for_a_smoke();

Generates a manual page with a WARNING section.

Write generated files into directory dir rather than the current directory. If dir is specified as -, generated pages are written to the standard output, separated by form-feeds.
Also output declarations for variables defined in the file.
Output manual pages for all static identifiers.
Group all the info generated together into a single page (ala ctype(3)), reading the single-line terse description for the NAME section from the line of the first comment in the file. If this first line contains a dash (-) surrounded by whitespace, the terse description is taken starting after the dash. If multiple files are specified, the first such suitable comment encountered is used. A link to the output file is made for each identifier documented, according to the -l option.
Like -g, but using the specified terse description rather than reading it from the file.
Don't attempt to fix up capitalization and punctuation.
If a function lacks a preceding comment, look for one immediately following the curly-brace at the top of the function body. The comment must appear before anything else.
Apply -b strictly. Only look for the description of a function at the top of its body.
-l h|s|f|n|r
Select how the output for a grouped manual page is linked to files named after all identifiers documented on the page. Hard link (h) is the default, as it uses the least space. Soft link (s), where supported, allows a find(1) command with ``-type f'' to easily skip the duplicated pages. Separate file (f) containing a file include directive is the traditional UNIX method. No link (n) is useful for generating printed documentation without duplicated pages; only a single file, named according to the -n option, is generated. Remove (r) is like No link, but also removes any previously generated links/files named after the identifiers documented. Useful for cleaning up after accidents with the other link options.

In all cases, any existing links will be removed before being rewritten.

Name the documentation output file after the input file. When generating grouped manual pages, this will be the file to which others are linked. For non-grouped manual pages, if documentation for more than one identifier is generated, information about the last identifier will overwrite information about all the previous ones.



Insert a #include line referencing the specified file in the SYNOPSIS section, using the ``<file>'' form by default. Any number of -i options may be specified to build up a list of prerequisites. If using the second form, you may need to quote the quotation marks, lest they get removed by the shell.
Exclude sectionname from the generated man pages. This option may be repeated to exclude a number of sections.
Prepend header-path to the name of the header file when an #include line is automatically generated in the SYNOPSIS section.
Lazy option: Only list parameters in the PARAMETERS section if they are documented by a comment in the source. By default, parameters with no comment are described as ``Not Documented.'', to encourage the programmer to comment them.
Set the output typesetting language as well as language specific options. options is a comma delimited list of options. Nroff (n) is the default, LaTeX (l) , Texinfo (t) , HTML (h) , AutoDoc (a). , or Raw text (r). Texinfo specific options are s, t, n, and C.

In Texinfo mode, each section is normally coded as a ``heading'' rather than a ``section''. This prevents the section name from appearing in the table of contents. If the option t is given, the name of the man page is used for the title of the NAME section, and is encoded as a ``section'', placing it in the table of contents. Subsequent sections are encoded as ``headings''. Texinfo supports multiple levels of headings; the desired level may be specified via the sn option, where n starts at 0 for the ``chapter level'' and works down. A top level node is created for the man page, except when in embedded mode (the c2man -e option). If the n option is specified, a node is created in embedded mode, but without Up, Previous, or Next pointers; these must be filled in (Texinfo mode in emacs does a good job of it). The C option capitalizes the section titles. Usually they are printed as specified (which is usually upper case).

Prepares the output so it can be embedded in texts of the output typesetting language.
Set the name of the manual in which the page will go.
Set the default manual section, used as the extension on the output files. section defaults to ``3'' for nroff, ``texi'' for Texinfo , ``html'' for HTML and ``tex'' for LaTeX output, as specified via the -T option. This setting can be overridden by the -O?.ext options for finer control.
Provides for finer control of the output files, allowing a different output subdirectory and extension to be specified for these different classes of objects: functions (f), variables (v), static functions (F) and static variables (V).

If subdir is specified, the selected class of output will be written in that subdirectory under the directory given by the -o option if specified, otherwise under the current directory.

If .ext is specified, it will be used as the extension on the output files of the selected class, instead of the default based on the -S option (if specified), or the typesetting output format specified by the -T option.

For example, the following command will generate nroff(1) style output under the /usr/local/man hierarchy, documenting functions in section 3 (/usr/local/man/man3/*.3), global variables in section 3v (/usr/local/man/man3/*.3v), static functions in section 9 (/usr/local/man/man9/*.9) and static variables in section 9v (/usr/local/man/man9/*.9v):

% c2man -o/usr/local/man -v -s -Ofman3.3 -Ovman3.3v -OFman9.9 -OVman9.9v input.c

The -O options will have no effect if -o- is used to write to standard output, and -Ov, -OF and -OV will have no effect unless their classes of output are enabled via the appropriate -v and -s options.

Set the format used to output the prototype for functions with more than 1 parameter in each manual page; functions with zero or 1 parameters are always output as one line. The format is specified by a template in the form
" int f ( a, b )"

but you may replace each space in this string with any number of whitespace characters. For example, the option
-F"int f(\n\ta,\n\tb\n\t)"

5 will produce: int main(
        int argc,
        char *argv[]

5 The default output format is: int main
        int argc,
        char *argv[]
Run a different C preprocessor than normal (use -V to determine the configured default). You must include any options required to prevent it from stripping comments, which is normally the default preprocessor behaviour. For example, to use gcc's cpp instead:

% c2man -P "gcc -E -C"

This option is passed through to the preprocessor and is used to define symbols for use with conditionals such as #ifdef.
This option is passed through to the preprocessor and is used to remove any definitions of this symbol.
This option is passed through to the preprocessor and is used to specify a directory to search for files that are referenced with #include.
Print version information and cpp parameters.

A few example input files, showing different commenting styles.

man(1), apropos(1), catman(8), cproto(1), cc(1), cpp(1)

c2man's error messages are not very helpful, so make sure your code compiles before trying c2man. If the code compiles OK but c2man rejects it, it may be because a comment is in a position c2man does not accept, or you are using a compiler extension not strictly conforming to standard C. c2man defines the preprocessor symbol __C2MAN__ with its major version number to allow you to work around such problems by surrounding them with #ifndef __C2MAN__.

An error at the very end of a function may indicate that the comments at the beginning are badly placed.

c2man was originally written by:

Graham Stoney Canon Information Systems Research Australia (please send bug reports here)

Many thanks are due to the many other Internet contributors since then, and to Chin Huang, the author of cproto from which it was originally derived.

The -F option only interprets the following character escape sequences:
2 \n	newline
\t	tab

A comment before a preprocessor directive will be considered to apply to the identifier that immediately follows, if it has no comment of its own. This is because the preprocessor directive gets removed by cpp before c2man looks at it.

Comments aren't legal in some of the more obscure places that they are in C.

Heavy use of #define in a program may yield somewhat obscure manual pages.

c2man's output backends may not be entirely consistent, but then users of different formatters tend to have different tastes.

February 25, 2000

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