CTAGS(1)

NAME
ctags - Generate C and C++ language tag files for use with vi(1)

SYNOPSIS

ctags
    [ -aBeFnNuwWx ] [ -f tagfile ] [ -h list ]
    [ -i types ] [ -I ignorelist ] [ -L listfile ]
    [ -p path ] [ -o tagfile ] [ --append ]
    [ --excmd=m|n|p ] [ --format=level ] [ --help ]
    [ --if0 ] [ --sort ] [ --totals ] [ --version ]
    [ file(s) ]

etags
    [ -ax ] [ -f tagfile ] [ -h list ] [ -i types ]
    [ -I ignorelist ] [ -L listfile ] [ -p path ]
    [ -o tagfile ] [ --append ] [ --help ] [ --if0 ]
    [ --totals ] [ --version ] [ file(s) ]

DESCRIPTION
The ctags and etags programs (hereinafter collectively referred to as ctags, except where distinguished) generate an index (or "tag") file of C and C++ language objects found in file(s) that allows these items to be quickly and easily located by a text editor or other utility. A "tag" signifies a C language object for which an index entry is available (or, alternatively, the index entry created for that object).

Alternatively, ctags can generate a cross reference file which lists, in human readable form, information about the various objects found in a set of C or C++ language files.

Tag index files are supported by the vi(1) editor and its derivatives (such as vim, elvis, stevie, and xvi), and by the emacs editor (see the HOW TO USE WITH sections, below), all of which allow the user to locate the object associated with a name appearing in a source file and jump to the file and line which defines the name. The following types of tags are supported by ctags:

    class names
    macro definitions (names created by #define)
    enum names
    enumerators (values inside an enumeration)
    function (method) definitions
    function (method) prototypes/declarations
    class, structure, and union data members
    struct names
    typedefs
    union names
    variables

Ctags only generates tags for objects which have global scoping (file-wide visibility). This means that, with the exception of macro definitions, only objects defined outside of brace enclosed function blocks are candidates for a tag.

OPTIONS

Despite the wealth of available options, defaults are set so that ctags is most commonly executed without any options (e.g. "ctags *.[ch]"), which will create a tag file in the current directory for the specified files. The options described below are provided merely to allow custom tailoring to meet special needs.

Note that spaces separating the single-letter options from their parameters are optional.

Note also that the boolean parameters to the long form options (those beginning with "--" and that take a "=yes|no" parameter) may be omitted, in which case "=yes" is implied. (e.g. --sort is equivalent to --sort=yes).

-a  Append the tags to an existing tag file. Equivalent to --append.

-B  Use backward searching patterns (e.g. ?regexp?).

-e  Output tag file for use with Emacs. If this program is executed by the name etags, this option is set by default. Selecting this option causes the following options to be ignored: -BFnNsuwW, --excmd, --format, --sort.

-f tagfile
    Use the name specified by tagfile for the tag file (default is "tags", or "TAGS" when using the -e option). If tagfile is specified as "-", then the tag file is written to standard output instead. Ctags will stubbornly refuse to take orders if tagfile exists and its first line contains something other than a valid tags line. This will save your neck if you mistakenly type "ctags -f *.c", which would otherwise overwrite your first C file with the tags generated by the rest!

-F  Use forward searching patterns (e.g. /regexp/) (default).

-h list
    Specifies a list of file extensions used for headers, separated by either periods or commas. The default list is ".h.H.hh.hpp.hxx.h++".

-i types
    Specifies the list of tag types to include in the output file. Types is a group of letters designating the types of tags affected. Each letter or group of letters may be preceded by either a '+' sign (default, if omitted) to add it to those already included, a '-' sign to exclude it from the list (e.g. to exclude a default tag type), or an '=' sign to include its corresponding tag type at the exclusion of those not listed. Tags for the following language contructs are supported (default settings are shown in brackets):
    c   class names
    d   macro definitions
    e   enumerators (values inside an enumeration)
    f   function (or method) definitions
    g   enumeration names
    m   class, structure, and union data members
    p   external function prototypes
    s   structure names
    t   typedefs
    u   union names
    v   variable definitions
    In addition, the following modifiers are accepted:
    C   Include a second tag entry for each class method and member (when selected) in the form "class::member". This allows locating class-qualified tags (e.g. ":tag class::member" in vi(1)).
    F   Include tags for the basename of each source file. This permits jumping to a file by its name (e.g. ":tag file.c" in vi(1)).
    S   Include static tags (those not visible outside of a single source file). Function and variable definitions are considered static only when their definitions are preceded with the "static" keyword. All other types of tags are considered static when they appear in a non-header file (see the -h option).
    The default value for types is "=cdefgtuvS" (i.e all tag types except for structure/class members and function prototypes; include static tags).

-I ignorelist
    Reads a list of names which are to be ignored while generating tags for the source files. The list may be supplied directly on the command line or found in a separate file. Normally, the parameter ignorelist is a list of names to be ignored, each separated with a comma, a semicolon, or white space (in which case the list should be quoted to keep the entire list as one command line argument). The parameter ignorelist will be interpreted as a filename if its first character is given as either a '.' or a pathname separator ('/' or '\'). In order to specify a file found in the current directory, use "./filename".

    This feature is useful when preprocessor macros are used in such a way that they cause syntactic confusion due to their presence. Some examples will illustrate this point.

    /* creates a global version string in module */ MODULE_VERSION("$Revision: 5.3 $")

    In this example, the macro invocation looks to much like a function definition because it is not followed by a semicolon (indeed, it could even be followed by a global variable definition that would look exactly like a K&R style function parameter declaration). In fact, this seeming function definition would likely cause the rest of the file to be skipped over while trying to complete the definition. Ignoring "MODULE_ID" would avoid such a problem.

    int foo ARGDECL2(void *, ptr, long int, nbytes)

    In this example, the macro "ARGDECL2" would be mistakenly interpreted to be the name of the function instead of the correct name of "foo". Ignoring the name "ARGDECL2" results in the correct behavior.

-L listfile
    Read from listfile a list of file names for which tags should be generated. If listfile is specified as "-", then file names are read from standard input.

-n  Equivalent to --excmd=number.

-N  Equivalent to --excmd=pattern.

-o tagfile
    Alternative for -f.

-p path
    Use path as the default directory for all supplied source files (whether supplied on the command line or in a file specified with the -L option), unless the source file is already specified as an absolute path. Note that this will not work together with wildcards in the filenames, since they are expanded by the shell.

-u  Equivalent to --sort=no.

-w  Exclude warnings about duplicate tags (default).

-W  Generate warnings about duplicate tags.

-x  Print a tabular, human-readable cross reference (xref) file to standard output instead of generating a tag file. The information contained in the output includes: the tag name; the kind of tag; the line number, file name, and source line (with extra white space condensed) of the file which defines the tag. No tag file is written and the following options will be ignored: -aBfFno, and -i+P. Example applications for this feature are generating a listing of all functions (including statics) located in a source file (e.g. ctags -xi=fS file), or generating a list of all externally visible global variables located in a source file (e.g. ctags -xi=v file).

--append=yes|no
    Indicates whether tags generated from the specified files should be appended to those already present in the tag file or should replace them. If the parameter is omitted, =yes is implied. This option is off by default.

--excmd=type
    Determines the type of EX command used to locate tags in the source file. The valid values for type are (either the entire word or the first letter is accepted):

    number
        Places into the tag file line numbers in the source file where tags are located rather than patterns to be searched for. This has three advantages:
        1.  Significantly reduces the size of the resulting tag file.
        2.  Eliminates failures to find tags because the line defining the tag has changed, causing the pattern match to fail (note that some editors, such as vim, are able to recover in many such instances).
        3.  Eliminates finding identical matching, but incorrect, source lines (see BUGS, below).
        However, this option has one significant drawback: changes to the source files can cause the line numbers recorded in the tag file to no longer correspond to the lines in the source file, causing jumps to some tags to miss the target definition by one or more lines. Basically, this option is best used when the source code to which it is applied is not subject to change. Selecting this option type causes the following options to be ignored: -BF.

    pattern
        Uses EX search patterns for all tags, rather than the line numbers usually used for macro definitions. This has the advantage of not referencing obsolete line numbers when lines have been added or removed since the tag file was generated.

    mixed
        Uses line numbers for macro definition tags and EX patterns for everything else. This is the default format generated by the original ctags and is, therefore, retained as the default for this option.

--format=level
    Change the format of the output tag file. Currently the only valid values for level are 1 or 2. Level 1 specifies the original tag file format and level 2 specifies a new extended format containing extension flags (but in a manner which retains backward compatibility with original vi(1) implementations). The default level is 2.

--help
    Prints to standard output a detailed usage description.

--if0=yes|no
    Indicates a preference as to whether code within an "#if 0" branch of a preprocessor conditional should be examined for non-macro tags (macro tags are always included). Because the intent of this construct is to disable code, the default value of this options is no. Note that this indicates a preference only and does not guarantee skipping code within an "#if 0" branch, since the fall-back algorithm used to generate tags when preprocessor conditionals are too complex follows all branches of a conditional. If the parameter is omitted, =yes is implied. This option is off by default.

--sort=yes|no
    Indicates whether the tag file should be sorted on the tag name (default is yes). Note that disabling sorting also disables the warning messages normally enabled by -W, because sorted tags are used to detect duplicate tags. Also note that the original vi(1) requires sorted tags. If the parameter is omitted, =yes is implied. This option is on by default for ctags, and ignored for etags.

--totals=yes|no
    Prints statistics about the source files read and the tag file written during the current invocation of ctags. If the parameter is omitted, =yes is implied. This option is off by default.

--version
    Prints a version identifier for ctags to standard output.

OPERATIONAL DETAILS
For every one of the qualified objects which are discovered in the source files supplied to ctags, a separate line is added to the tag file, each looking like this in the most general case:

    tag_name file_name ex_cmd;" xflags

The fields and separators of these lines are specified as follows:

    1.  tag name (a C language identifier)
    2.  a single tab character
    3.  the name of the file in which the object associated with the tag is located
    4.  a single tab character
    5.  an EX command to locate the tag within the file; generally a search pattern (either /pattern/ or ?pattern?) or line number (see --excmd). Tag file format 2 (see --format) extends this EX command under certain circumstances to include a set of extension flags embedded in an EX comment immediately appended to the EX command, which should make it backwards compatible with original vi(1).

A few special tags are written into the tag file for internal purposes. These tags are composed in such a way that they always sort to the top of the file. Therefore, the first two characters of these tags are used a magic number to detect a tag file for purposes of determining whether a valid tag file is being overwritten rather than a source file.

When this program is invoked by the name etags, or with the -e option, the output file is in a different format that is used by emacs(1).

Note that the name of each source file will be recorded in the tag file exactly as it appears on the command line. Therefore, if the path you specified on the command line was relative to some directory, then it will be recorded in that same manner in the tag file.

This version of ctags imposes no formatting requirements. Other versions of ctags tended to rely upon certain formatting assumptions in order to help it resolve coding dilemmas caused by preprocessor conditionals.

In general, ctags tries to be smart about conditional preprocessor directives. If a preprocessor conditional is encountered within a statement which defines a tag, ctags follows only the first branch of that conditional (except in the special case of "#if 0", in which case it follows only the last branch). The reason for this is that failing to pursue only one branch can result in ambiguous syntax, as in the following example:

    #ifdef TWO_ALTERNATIVES
    struct {
    #else
    union {
    #endif
        short a;
        long b;
    }

Both branches cannot be followed, or braces become unbalanced and ctags would be unable to make sense of the syntax.

If the application of this heuristic fails to properly parse a file, generally due to complicated and inconsistent pairing within the conditionals, ctags will retry the file using a different heuristic which does not selectively follow conditional preprocessor branches, but instead falls back to relying upon a closing brace ("}") in column 1 as indicating the end of a block once any brace imbalance results from following a #if conditional branch.

Ctags will also try to specially handle arguments lists enclosed in double sets of parentheses in order to accept the following conditional construct:

    extern void foo __ARGS((int one, char two));

Any name immediately preceding the "((" will be automatically ignored and the previous name will be used.

After creating or appending to the tag file, it is sorted by the tag name, removing identical tag lines.

Note that the path recorded for filenames in the tag file and utilized by the editor to search for tags are identical to the paths specified for file(s) on the command line. This means the if you want the paths for files to be relative to some directory, you must invoke ctags with the same pathnames for file(s) (this can be overridden with -p).

ENVIRONMENT VARIABLES

CTAGS
    This variable, if found, will be assumed to contain a set of custom default options which are read when ctags starts, but before any command line options are read. Options in this variable should be in the same form as those on the command line. Command line options will override options specified in this variable. Only options may be specified with this variable; no source file names are read from its value.

ETAGS
    Similar to the CTAGS variable above, this variable, if found, will be read when etags starts. If this variable is not found, etags will try to use CTAGS instead.

HOW TO USE WITH VI
Vi will, by default, expect a tag file by the name "tags" in the current directory. Once the tag file is built, the following commands exercise the tag indexing feature:

vi -t tag
    Start vi and position the cursor at the file and line where "tag" is defined.

Control-]
    Find the tag under the cursor.

:ta tag
    Find a tag.

Control-T
    Return to previous location before jump to tag (not widely implemented).

HOW TO USE WITH GNU EMACS
Emacs will, by default, expect a tag file by the name "TAGS" in the current directory. Once the tag file is built, the following commands exercise the tag indexing feature:

Meta-x visit-tags-table
    Visit a TAGS file.

Meta-.
    Find a definition for a tag. The default tag is the identifier under the cursor. There is name completion in the minibuffer; typing "foo TAB" completes the identifier starting with `foo' (`foobar', for example) or lists the alternatives.

Meta-,
    Find the next definition for the tag. Exact matches are found first, followed by fuzzier matches.

For more commands, see the Tags topic in the Emacs info tree.

BUGS
Because ctags does not look inside brace enclosed function blocks, local declarations of classes, enum/struct/union tags, enumeration values and variables within a function will not have tags generated for them.

Note that when ctags generates uses patterns for locating tags (see the --excmd option), it is entirely possible that the wrong line may be found by your editor if there exists another, identical, line (whose context prevents it from generating a tag) which is identical to the line containing the tag. The following example demonstrates this condition:

    int variable; /* ... */
    void foo(variable)
    int variable;
    {
        /* ... */
    }

Depending upon which editor you use and where in the code you happen to be, it is possible that the search pattern may locate the local parameter declaration in foo() before it finds the actual global variable definition, since the lines (and therefore their search patterns are identical). This can be avoided by use of the -n option.

Because ctags is neither a preprocessor nor a compiler, some complex or obscure constructs can fool ctags into either missing a tag or improperly generating an inappropriate tag. In particular, the use of preprocessor constructs which alter the textual syntax of C can fool ctags, as demonstrated by the following example:

    #ifdef GLOBAL
    #define EXTERN
    #define INIT(assign) assign
    #else
    #define EXTERN extern
    #define INIT(assign)
    #endif
    EXTERN BUF *firstbuf INIT(= NULL);

This looks too much like a declaration for a function called "INIT", which returns a pointer to a typedef "firstbuf", rather than the actual variable definition that it is, since this distinction can only be resolved by the preprocessor. The moral of the story: don't do this if you want a tag generated for it, or use the -I option to specify "INIT" as a keyword to be ignored.

FILES

tags
    The default tag file created by ctags.

TAGS
    The default tag file created by etags.

SEE ALSO
The official Exuberant Ctags web site at:

    http://home.hiwaay.net/~darren/ctags/

Also ex(1), vi(1), elvis, or, better yet, vim, the official editor of ctags. For more information on vim, see the VIM Pages web site at:

    http://www.vim.org/

AUTHOR
Darren Hiebert <darren@hiebert.com>
http://home.hiwaay.net/~darren

MOTIVATION
"Think ye at all times of rendering some service to every member of the human race."

"All effort and exertion put forth by man from the fullness of his heart is worship, if it is prompted by the highest motives and the will to do service to humanity."

    -- From the Baha'i Writings

CREDITS
This version of ctags was originally derived from and inspired by the ctags program by Steve Kirkendall <kirkenda@cs.pdx.edu> that comes with the Elvis vi clone (though virtually none of the original code remains).

Credit is also due Bram Moolenaar <mool@oce.nl>, the author of vim, who has devoted so much of his time and energy both to developing the editor as a service to others, and to helping the orphans of Uganda.

The section entitled "HOW TO USE WITH GNU EMACS" was shamelessly stolen from the man page for GNU etags.