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 out-
side 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 cus-
tom 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 oth-
erwise overwrite your first C file with the tags gen-
erated 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 exclu-
sion of those not listed. Tags for the following lan-
guage 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 vari-
able 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 cur-
rent directory, use "./filename".
This feature is useful when preprocessor macros are
used in such a way that they cause syntactic confu-
sion due to their presence. Some examples will illus-
trate 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 "MOD-
ULE_ID" would avoid such a problem.
int foo ARGDECL2(void *, ptr, long int, nbytes)
In this example, the macro "ARGDECL2" would be mis-
takenly 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 fol-
lowing 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 advan-
tage of not referencing obsolete line num-
bers 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 compat-
ibility with original vi(1) implementations). The
default level is 2.
--help
Prints to standard output a detailed usage descrip-
tion.
--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 gener-
ate tags when preprocessor conditionals are too com-
plex 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 discov-
ered 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 associ-
ated 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 for-
matting assumptions in order to help it resolve coding
dilemmas caused by preprocessor conditionals.
In general, ctags tries to be smart about conditional pre-
processor 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 unbal-
anced and ctags would be unable to make sense of the syn-
tax.
If the application of this heuristic fails to properly
parse a file, generally due to complicated and inconsis-
tent pairing within the conditionals, ctags will retry the
file using a different heuristic which does not selec-
tively 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 automati-
cally 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 identi-
cal 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 con-
tain 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 vari-
able, 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 con-
taining 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 inappro-
priate tag. In particular, the use of preprocessor con-
structs 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 offi-
cial editor of ctags. For more information on vim, see the
VIM Pages web site at:
http://www.vim.org/
AUTHOR
Darren Hiebert lt;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 full-
ness 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 <kirk-
enda@cs.pdx.edu> that comes with the Elvis vi clone
(though virtually none of the original code remains).
Credit is also due Bram Moolenaar lt;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 oth-
ers, 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.