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ctags - Generate tag files for source code


ctags [options] [file(s)]

etags [options] [file(s)]


The ctags and etags programs (hereinafter collectively referred to as ctags, except where
distinguished) generate an index (or "tag") file for a variety of language objects found
in file(s). This tag file allows these items to be quickly and easily located by a text
editor or other utility. A "tag" signifies a 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 source objects found in a set of language files.

Tag index files are supported by numerous editors, 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. Those known about at the time of this release are:

Vi(1) and its derivatives (e.g. Elvis, Vim, Vile, Lemmy), CRiSP, Emacs, FTE (Folding
Text Editor), JED, jEdit, Mined, NEdit (Nirvana Edit), TSE (The SemWare Editor),
UltraEdit, WorkSpace, X2, Zeus

Ctags is capable of generating different kinds of tags for each of many different
languages. For a complete list of supported languages, the names by which they are
recognized, and the kinds of tags which are generated for each, see the --list-languages
and --list-kinds options.


Unless the --language-force option is specified, the language of each source file is
automatically selected based upon a mapping of file names to languages. The mappings in
effect for each language may be display using the --list-maps option and may be changed
using the --langmap option. On platforms which support it, if the name of a file is not
mapped to a language and the file is executable, the first line of the file is checked to
see if the file is a "#!" script for a recognized language.

By default, all other files names are ignored. This permits running ctags on all files in
either a single directory (e.g. "ctags *"), or on all files in an entire source directory
tree (e.g. "ctags -R"), since only those files whose names are mapped to languages will be

[The reason that .h extensions are mapped to C++ files rather than C files is because it
is common to use .h extensions in C++, and no harm results in treating them as C++ files.]


Despite the wealth of available options, defaults are set so that ctags is most commonly
executed without any options (e.g. "ctags *", or "ctags -R"), which will create a tag file
in the current directory for all recognized source 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). Note further that "=1" and "=on" are considered
synonyms for "=yes", and that "=0" and "=off" are considered synonyms for "=no".

Some options are either ignored or useful only when used while running in etags mode (see
-e option). Such options will be noted.

Most options may appear anywhere on the command line, affecting only those files which
follow the option. A few options, however, must appear before the first file name and will
be noted as such.

Options taking language names will accept those names in either upper or lower case. See
the --list-languages option for a complete list of the built-in language names.

-a Equivalent to --append.

-B Use backward searching patterns (e.g. ?pattern?). [Ignored in etags mode]

-e Enable etags mode, which will create a tag file for use with the Emacs editor.
Alternatively, if ctags is invoked by a name containing the string "etags" (either by
renaming, or creating a link to, the executable), etags mode will be enabled. This
option must appear before the first file name.

-f tagfile
Use the name specified by tagfile for the tag file (default is "tags", or "TAGS" when
running in etags mode). 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! It will also refuse to accept
a multi-character file name which begins with a '-' (dash) character, since this most
likely means that you left out the tag file name and this option tried to grab the
next option as the file name. If you really want to name your output tag file
"-ugly", specify it as "./-ugly". This option must appear before the first file name.
If this option is specified more than once, only the last will apply.

-F Use forward searching patterns (e.g. /pattern/) (default). [Ignored in etags mode]

-h list
Specifies a list of file extensions, separated by periods, which are to be
interpreted as include (or header) files. To indicate files having no extension, use
a period not followed by a non-period character (e.g. ".", "..x", ".x."). This option
only affects how the scoping of a particular kinds of tags is interpreted (i.e.
whether or not they are considered as globally visible or visible only within the
file in which they are defined); it does not map the extension to any particular
language. Any tag which is located in a non-include file and cannot be seen (e.g.
linked to) from another file is considered to have file-limited (e.g. static) scope.
No kind of tag appearing in an include file will be considered to have file-limited
scope. If the first character in the list is a plus sign, then the extensions in the
list will be appended to the current list; otherwise, the list will replace the
current list. See, also, the --file-scope option. The default list is
".h.H.hh.hpp.hxx.h++.inc.def". To restore the default list, specify -h default. Note
that if an extension supplied to this option is not already mapped to a particular
language (see SOURCE FILES, above), you will also need to use either the --langmap or
--language-force option.

-I identifier-list
Specifies a list of identifiers which are to be specially handled while parsing C and
C++ source files. This option is specifically provided to handle special cases
arising through the use of preprocessor macros. When the identifiers listed are
simple identifiers, these identifiers will be ignored during parsing of the source
files. If an identifier is suffixed with a '+' character, ctags will also ignore any
parenthesis-enclosed argument list which may immediately follow the identifier in the
source files. If two identifiers are separated with the '=' character, the first
identifiers is replaced by the second identifiers for parsing purposes. The list of
identifiers may be supplied directly on the command line or read in from a separate
file. If the first character of identifier-list is '@', '.' or a pathname separator
('/' or '\'), or the first two characters specify a drive letter (e.g. "C:"), the
parameter identifier-list will be interpreted as a filename from which to read a list
of identifiers, one per input line. Otherwise, identifier-list is a list of
identifiers (or identifier pairs) to be specially handled, each delimited by a either
a comma or by white space (in which case the list should be quoted to keep the entire
list as one command line argument). Multiple -I options may be supplied. To clear
the list of ignore identifiers, supply a single dash ("-") for identifier-list.

This feature is useful when preprocessor macros are used in such a way that they
cause syntactic confusion due to their presence. Indeed, this is the best way of
working around a number of problems caused by the presence of syntax-busting macros
in source files (see CAVEATS, below). Some examples will illustrate this point.

int foo ARGDECL4(void *, ptr, long int, nbytes)

In the above example, the macro "ARGDECL4" would be mistakenly interpreted to be the
name of the function instead of the correct name of "foo". Specifying -I ARGDECL4
results in the correct behavior.

/* creates an RCS version string in module */
MODULE_VERSION("$Revision: 750 $")

In the above example the macro invocation looks too 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 much like a K&R style function parameter
declaration). In fact, this seeming function definition could possibly even cause the
rest of the file to be skipped over while trying to complete the definition.
Specifying -I MODULE_VERSION+ would avoid such a problem.

CLASS Example {
// your content here

The example above uses "CLASS" as a preprocessor macro which expands to something
different for each platform. For instance CLASS may be defined as "class
__declspec(dllexport)" on Win32 platforms and simply "class" on UNIX. Normally, the
absence of the C++ keyword "class" would cause the source file to be incorrectly
parsed. Correct behavior can be restored by specifying -I CLASS=class.

-L file
Read from file a list of file names for which tags should be generated. If file is
specified as "-", then file names are read from standard input. File names read using
this option are processed following file names appearing on the command line. Options
are also accepted in this input. If this option is specified more than once, only the
last will apply. Note: file is read in line-oriented mode, where a new line is the
only delimiter and non-trailing white space is considered significant, in order that
file names containing spaces may be supplied (however, trailing white space is
stripped from lines); this can affect how options are parsed if included in the

-n Equivalent to --excmd=number.

-N Equivalent to --excmd=pattern.

-o tagfile
Equivalent to -f tagfile.

-R Equivalent to --recurse.

-u Equivalent to --sort=no (i.e. "unsorted").

-V Equivalent to --verbose.

-w This option is silently ignored for backward-compatibility with the ctags of SVR4

-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 all options affecting tag file output will be ignored. Example
applications for this feature are generating a listing of all functions located in a
source file (e.g. ctags -x --c-kinds=f file), or generating a list of all externally
visible global variables located in a source file (e.g. ctags -x --c-kinds=v
--file-scope=no file). This option must appear before the first file name.

Indicates whether tags generated from the specified files should be appended to those
already present in the tag file or should replace them. This option is off by
default. This option must appear before the first file name.

Include a reference to file in the tag file. This option may be specified as many
times as desired. This supports Emacs' capability to use a tag file which "includes"
other tag files. [Available only in etags mode]

Add pattern to a list of excluded files and directories. This option may be specified
as many times as desired. For each file name considered by ctags, each pattern
specified using this option will be compared against both the complete path (e.g.
some/path/base.ext) and the base name (e.g. base.ext) of the file, thus allowing
patterns which match a given file name irrespective of its path, or match only a
specific path. If appropriate support is available from the runtime library of your C
compiler, then pattern may contain the usual shell wildcards (not regular
expressions) common on Unix (be sure to quote the option parameter to protect the
wildcards from being expanded by the shell before being passed to ctags; also be
aware that wildcards can match the slash character, '/'). You can determine if shell
wildcards are available on your platform by examining the output of the --version
option, which will include "+wildcards" in the compiled feature list; otherwise,
pattern is matched against file names using a simple textual comparison.

If pattern begins with the character '@', then the rest of the string is interpreted
as a file name from which to read exclusion patterns, one per line. If pattern is
empty, the list of excluded patterns is cleared. Note that at program startup, the
default exclude list contains "EIFGEN", "SCCS", "RCS", and "CVS", which are names of
directories for which it is generally not desirable to descend while processing the
--recurse option.

Determines the type of EX command used to locate tags in the source file. [Ignored
in etags mode]

The valid values for type (either the entire word or the first letter is accepted)

number Use only line numbers in the tag file for locating tags. This has four
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).
4. Retains separate entries in the tag file for lines which are identical
in content. In pattern mode, duplicate entries are dropped because the
search patterns they generate are identical, making the duplicate
entries useless.

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 Use only 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 In this mode, patterns are generally used with a few exceptions. For C, line
numbers are used for macro definition tags. This was the default format
generated by the original ctags and is, therefore, retained as the default
for this option. For Fortran, line numbers are used for common blocks
because their corresponding source lines are generally identical, making
pattern searches useless for finding all matches.

Specifies whether to include extra tag entries for certain kinds of information. The
parameter flags is a set of one-letter flags, each representing one kind of extra tag
entry to include in the tag file. If flags is preceded by either the '+' or '-'
character, the effect of each flag is added to, or removed from, those currently
enabled; otherwise the flags replace any current settings. The meaning of each flag
is as follows:

f Include an entry for the base file name of every source file (e.g.
"example.c"), which addresses the first line of the file.

q Include an extra class-qualified tag entry for each tag which is a member of a
class (for languages for which this information is extracted; currently C++,
Eiffel, and Java). The actual form of the qualified tag depends upon the
language from which the tag was derived (using a form that is most natural for
how qualified calls are specified in the language). For C++, it is in the form
"class::member"; for Eiffel and Java, it is in the form "class.member". This
may allow easier location of a specific tags when multiple occurrences of a
tag name occur in the tag file. Note, however, that this could potentially
more than double the size of the tag file.

Specifies the available extension fields which are to be included in the entries of
the tag file (see TAG FILE FORMAT, below, for more information). The parameter flags
is a set of one-letter flags, each representing one type of extension field to
include, with the following meanings (disabled by default unless indicated):

a Access (or export) of class members
f File-restricted scoping [enabled]
i Inheritance information
k Kind of tag as a single letter [enabled]
K Kind of tag as full name
l Language of source file containing tag
m Implementation information
n Line number of tag definition
s Scope of tag definition [enabled]
S Signature of routine (e.g. prototype or parameter list)
z Include the "kind:" key in kind field
t Type and name of a variable or typedef as "typeref:" field [enabled]

Each letter or group of letters may be preceded by either '+' to add it to the
default set, or '-' to exclude it. In the absence of any preceding '+' or '-' sign,
only those kinds explicitly listed in flags will be included in the output (i.e.
overriding the default set). This option is ignored if the option --format=1 has been
specified. The default value of this option is fkst.

Indicates whether tags scoped only for a single file (i.e. tags which cannot be seen
outside of the file in which they are defined, such as "static" tags) should be
included in the output. See, also, the -h option. This option is enabled by default.

Causes ctags to behave as a filter, reading source file names from standard input and
printing their tags to standard output on a file-by-file basis. If --sorted is
enabled, tags are sorted only within the source file in which they are defined. File
names are read from standard input in line-oriented input mode (see note for -L
option) and only after file names listed on the command line or from any file
supplied using the -L option. When this option is enabled, the options -f, -o, and
--totals are ignored. This option is quite esoteric and is disabled by default. This
option must appear before the first file name.

Specifies a string to print to standard output following the tags for each file name
parsed when the --filter option is enabled. This may permit an application reading
the output of ctags to determine when the output for each file is finished. Note that
if the file name read is a directory and --recurse is enabled, this string will be
printed only once at the end of all tags found for by descending the directory. This
string will always be separated from the last tag line for the file by its
terminating newline. This option is quite esoteric and is empty by default. This
option must appear before the first file name.

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 fields (but in a manner which retains
backward-compatibility with original vi(1) implementations). The default level is 2.
This option must appear before the first file name. [Ignored in etags mode]

Prints to standard output a detailed usage description, and then exits.

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
option 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. This option is disabled by default.

Specifies a list of language-specific kinds of tags (or kinds) to include in the
output file for a particular language, where <LANG> is case-insensitive and is one of
the built-in language names (see the --list-languages option for a complete list).
The parameter kinds is a group of one-letter flags designating kinds of tags
(particular to the language) to either include or exclude from the output. The
specific sets of flags recognized for each language, their meanings and defaults may
be list using the --list-kinds option. Each letter or group of letters may be
preceded by either '+' to add it to, or '-' to remove it from, the default set. In
the absence of any preceding '+' or '-' sign, only those kinds explicitly listed in
kinds will be included in the output (i.e. overriding the default for the specified

As an example for the C language, in order to add prototypes and external variable
declarations to the default set of tag kinds, but exclude macros, use
--c-kinds=+px-d; to include only tags for functions, use --c-kinds=f.

Defines a new user-defined language, name, to be parsed with regular expressions.
Once defined, name may be used in other options taking language names. The typical
use of this option is to first define the language, then map file names to it using
--langmap, then specify regular expressions using --regex-<LANG> to define how its
tags are found.

Controls how file names are mapped to languages (see the --list-maps option). Each
comma-separated map consists of the language name (either a built-in or user-defined
language), a colon, and a list of file extensions and/or file name patterns. A file
extension is specified by preceding the extension with a period (e.g. ".c"). A file
name pattern is specified by enclosing the pattern in parentheses (e.g.
"([Mm]akefile)"). If appropriate support is available from the runtime library of
your C compiler, then the file name pattern may contain the usual shell wildcards
common on Unix (be sure to quote the option parameter to protect the wildcards from
being expanded by the shell before being passed to ctags). You can determine if shell
wildcards are available on your platform by examining the output of the --version
option, which will include "+wildcards" in the compiled feature list; otherwise, the
file name patterns are matched against file names using a simple textual comparison.
When mapping a file extension, it will first be unmapped from any other languages.

If the first character in a map is a plus sign, then the extensions and file name
patterns in that map will be appended to the current map for that language;
otherwise, the map will replace the current map. For example, to specify that only
files with extensions of .c and .x are to be treated as C language files, use
"--langmap=c:.c.x"; to also add files with extensions of .j as Java language files,
specify "--langmap=c:.c.x,java:+.j". To map makefiles (e.g. files named either
"Makefile", "makefile", or having the extension ".mak") to a language called "make",
specify "--langmap=make:([Mm]akefile).mak". To map files having no extension,
specify a period not followed by a non-period character (e.g. ".", "..x", ".x."). To
clear the mapping for a particular language (thus inhibiting automatic generation of
tags for that language), specify an empty extension list (e.g.
"--langmap=fortran:"). To restore the default language mappings for all a particular
language, supply the keyword "default" for the mapping. To specify restore the
default language mappings for all languages, specify "--langmap=default". Note that
file extensions are tested before file name patterns when inferring the language of a

By default, ctags automatically selects the language of a source file, ignoring those
files whose language cannot be determined (see SOURCE FILES, above). This option
forces the specified language (case-insensitive; either built-in or user-defined) to
be used for every supplied file instead of automatically selecting the language based
upon its extension. In addition, the special value auto indicates that the language
should be automatically selected (which effectively disables this option).

Specifies the languages for which tag generation is enabled, with list containing a
comma-separated list of language names (case-insensitive; either built-in or user-
defined). If the first language of list is not preceded by either a '+' or '-', the
current list will be cleared before adding or removing the languages in list. Until a
'-' is encountered, each language in the list will be added to the current list. As
either the '+' or '-' is encountered in the list, the languages following it are
added or removed from the current list, respectively. Thus, it becomes simple to
replace the current list with a new one, or to add or remove languages from the
current list. The actual list of files for which tags will be generated depends upon
the language extension mapping in effect (see the --langmap option). Note that all
languages, including user-defined languages are enabled unless explicitly disabled
using this option. Language names included in list may be any built-in language or
one previously defined with --langdef. The default is "all", which is also accepted
as a valid argument. See the --list-languages option for a complete list of the
built-in language names.

Prints a summary of the software license to standard output, and then exits.

Specifies whether "#line" directives should be recognized. These are present in the
output of preprocessors and contain the line number, and possibly the file name, of
the original source file(s) from which the preprocessor output file was generated.
When enabled, this option will cause ctags to generate tag entries marked with the
file names and line numbers of their locations original source file(s), instead of
their actual locations in the preprocessor output. The actual file names placed into
the tag file will have the same leading path components as the preprocessor output
file, since it is assumed that the original source files are located relative to the
preprocessor output file (unless, of course, the #line directive specifies an
absolute path). This option is off by default. Note: This option is generally only
useful when used together with the --excmd=number (-n) option. Also, you may have to
use either the --langmap or --language-force option if the extension of the
preprocessor output file is not known to ctags.

Indicates whether symbolic links (if supported) should be followed. When disabled,
symbolic links are ignored. This option is on by default.

Lists the tag kinds recognized for either the specified language or all languages,
and then exits. Each kind of tag recorded in the tag file is represented by a one-
letter flag, which is also used to filter the tags placed into the output through use
of the --<LANG>-kinds option. Note that some languages and/or tag kinds may be
implemented using regular expressions and may not be available if regex support is
not compiled into ctags (see the --regex-<LANG> option). Each kind listed is enabled
unless followed by "[off]".

Lists the file extensions and file name patterns which associate a file name with a
language for either the specified language or all languages, and then exits. See the
--langmap option, and SOURCE FILES, above.

Lists the names of the languages understood by ctags, and then exits. These language
names are case insensitive and may be used in the --language-force, --languages,
--<LANG>-kinds, and --regex-<LANG> options.

Read additional options from file. The file should contain one option per line. As a
special case, if --options=NONE is specified as the first option on the command line,
it will disable the automatic reading of any configuration options from either a file
or the environment (see FILES).

Recurse into directories encountered in the list of supplied files. If the list of
supplied files is empty and no file list is specified with the -L option, then the
current directory (i.e. ".") is assumed. Symbolic links are followed. If you don't
like these behaviors, either explicitly specify the files or pipe the output of
find(1) into ctags -L- instead. Note: This option is not supported on all platforms
at present. It is available if the output of the --help option includes this option.
See, also, the --exclude to limit recursion.

The /regexp/replacement/ pair define a regular expression replacement pattern,
similar in style to sed substitution commands, with which to generate tags from
source files mapped to the named language, <LANG>, (case-insensitive; either a built-
in or user-defined language). The regular expression, regexp, defines an extended
regular expression (roughly that used by egrep(1)), which is used to locate a single
source line containing a tag and may specify tab characters using \t. When a matching
line is found, a tag will be generated for the name defined by replacement, which
generally will contain the special back-references \1 through \9 to refer to matching
sub-expression groups within regexp. The '/' separator characters shown in the
parameter to the option can actually be replaced by any character. Note that
whichever separator character is used will have to be escaped with a backslash ('\')
character wherever it is used in the parameter as something other than a separator.
The regular expression defined by this option is added to the current list of regular
expressions for the specified language unless the parameter is omitted, in which case
the current list is cleared.

Unless modified by flags, regexp is interpreted as a Posix extended regular
expression. The replacement should expand for all matching lines to a non-empty
string of characters, or a warning message will be reported. An optional kind
specifier for tags matching regexp may follow replacement, which will determine what
kind of tag is reported in the "kind" extension field (see TAG FILE FORMAT, below).
The full form of kind-spec is in the form of a single letter, a comma, a name
(without spaces), a comma, a description, followed by a separator, which specify the
short and long forms of the kind value and its textual description (displayed using
--list-kinds). Either the kind name and/or the description may be omitted. If
kind-spec is omitted, it defaults to "r,regex". Finally, flags are one or more
single-letter characters having the following effect upon the interpretation of

b The pattern is interpreted as a Posix basic regular expression.

e The pattern is interpreted as a Posix extended regular expression (default).

i The regular expression is to be applied in a case-insensitive manner.

Note that this option is available only if ctags was compiled with support for
regular expressions, which depends upon your platform. You can determine if support
for regular expressions is compiled in by examining the output of the --version
option, which will include "+regex" in the compiled feature list.

For more information on the regular expressions used by ctags, see either the
regex(5,7) man page, or the GNU info documentation for regex (e.g. "info regex").

Indicates whether the tag file should be sorted on the tag name (default is yes).
Note that the original vi(1) required sorted tags. The foldcase value specifies case
insensitive (or case-folded) sorting. Fast binary searches of tag files sorted with
case-folding will require special support from tools using tag files, such as that
found in the ctags readtags library, or Vim version 6.2 or higher (using "set
ignorecase"). This option must appear before the first file name. [Ignored in etags

Indicates that the file paths recorded in the tag file should be relative to the
directory containing the tag file, rather than relative to the current directory,
unless the files supplied on the command line are specified with absolute paths. This
option must appear before the first file name. The default is yes when running in
etags mode (see the -e option), no otherwise.

Prints statistics about the source files read and the tag file written during the
current invocation of ctags. This option is off by default. This option must appear
before the first file name.

Enable verbose mode. This prints out information on option processing and a brief
message describing what action is being taken for each file considered by ctags.
Normally, ctags does not read command line arguments until after options are read
from the configuration files (see FILES, below) and the CTAGS environment variable.
However, if this option is the first argument on the command line, it will take
effect before any options are read from these sources. The default is no.

Prints a version identifier for ctags to standard output, and then exits. This is
guaranteed to always contain the string "Exuberant Ctags".


As ctags considers each file name in turn, it tries to determine the language of the file
by applying the following three tests in order: if the file extension has been mapped to a
language, if the file name matches a shell pattern mapped to a language, and finally if
the file is executable and its first line specifies an interpreter using the Unix-style
"#!" specification (if supported on the platform). If a language was identified, the file
is opened and then the appropriate language parser is called to operate on the currently
open file. The parser parses through the file and adds an entry to the tag file for each
language object it is written to handle. See TAG FILE FORMAT, below, for details on these

This implementation of ctags imposes no formatting requirements on C code as do legacy
implementations. Older implementations of ctags tended to rely upon certain formatting
assumptions in order to help it resolve coding dilemmas caused by preprocessor

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:

struct {
union {
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.

C++ operator definitions are specially handled. In order for consistency with all types of
operators (overloaded and conversion), the operator name in the tag file will always be
preceded by the string "operator " (i.e. even if the actual operator definition was
written as "operator<<").

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


When not running in etags mode, each entry in the tag file consists of a separate line,
each looking like this in the most general case:


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

1. tag name
2. single tab character
3. name of the file in which the object associated with the tag is located
4. single tab character
5. EX command used 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 fields (described below) embedded in an EX comment immediately
appended to the EX command, which leaves it backward-compatible with original
vi(1) implementations.

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.

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 the current directory, then it will be recorded in that same manner in the tag
file. See, however, the --tag-relative option for how this behavior can be modified.

Extension fields are tab-separated key-value pairs appended to the end of the EX command
as a comment, as described above. These key value pairs appear in the general form
"key:value". Their presence in the lines of the tag file are controlled by the --fields
option. The possible keys and the meaning of their values are as follows:

access Indicates the visibility of this class member, where value is specific to the

file Indicates that the tag has file-limited visibility. This key has no
corresponding value.

kind Indicates the type, or kind, of tag. Its value is either one of the
corresponding one-letter flags described under the various --<LANG>-kinds
options above, or a full name. It is permitted (and is, in fact, the default)
for the key portion of this field to be omitted. The optional behaviors are
controlled with the --fields option.

When present, this indicates a limited implementation (abstract vs. concrete)
of a routine or class, where value is specific to the language ("virtual" or
"pure virtual" for C++; "abstract" for Java).

inherits When present, value. is a comma-separated list of classes from which this
class is derived (i.e. inherits from).

signature When present, value is a language-dependent representation of the signature of
a routine. A routine signature in its complete form specifies the return type
of a routine and its formal argument list. This extension field is presently
supported only for C-based languages and does not include the return type.

In addition, information on the scope of the tag definition may be available, with the key
portion equal to some language-dependent construct name and its value the name declared
for that construct in the program. This scope entry indicates the scope in which the tag
was found. For example, a tag generated for a C structure member would have a scope
looking like "struct:myStruct".


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.

:ta tag Find a tag.

Ctrl-] Find the tag under the cursor.

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


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:

M-x visit-tags-table <RET> FILE <RET>
Select the tag file, "FILE", to use.

M-. [TAG] <RET>
Find the first definition of TAG. The default tag is the identifier under the

M-* Pop back to where you previously invoked "M-.".

C-u M-. Find the next definition for the last tag.

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


NEdit version 5.1 and later can handle the new extended tag file format (see --format). To
make NEdit use the tag file, select "File->Load Tags File". To jump to the definition for
a tag, highlight the word, then press Ctrl-D. NEdit 5.1 can can read multiple tag files
from different directories. Setting the X resource nedit.tagFile to the name of a tag
file instructs NEdit to automatically load that tag file at startup time.


Because ctags is neither a preprocessor nor a compiler, use of preprocessor macros can
fool ctags into either missing tags or improperly generating inappropriate tags. Although
ctags has been designed to handle certain common cases, this is the single biggest cause
of reported problems. In particular, the use of preprocessor constructs which alter the
textual syntax of C can fool ctags. You can work around many such problems by using the -I

Note that since ctags generates 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
source line 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 --excmd=n option.

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