CTAGS (1)

SYNOPSIS

ctags [options] [file(s)]

etags [options] [file(s)]

DESCRIPTION

The ctags and etags programs (hereinafter collectively referred to as ctags, except where distinguished) generate an index (or "tag") file for C, C++, Eiffel, Fortran, and Java 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 release are:

vi(1) and its many derivatives emacs CRiSP FTE (Folding Text Editor) Lemmy NEdit TSE (The SemWare Editor) Zeus

ctags is capable of generating tags for all of the following language constructs:

C/C++:
macros (names defined/undefined by #define/#undef) enumerators (enumerated values) function definitions, prototypes, and declarations class, enum, struct, and union names namespaces typedefs variables (definitions and declarations) class, struct, and union members
Eiffel:
classes features local entities
Fortran:
block data common blocks entry points functions interfaces labels modules namelists programs subroutines derived types
Java:
classes fields interfaces methods packages

SOURCE FILES

The language of each source file is automatically selected based upon its file extension (unless the --lang option is specified). File extensions are mapped to source file languages according to the following default mapping (unless the --langmap option is specified):

C

*.c

C++

*.C *.c++ *.cc *.cpp *.cxx *.h *.H *.hh *.hpp *.hxx *.h++

Eiffel

*.e

Fortran

*.f *.for *.ftn *.f77 *.f90 *.F *.FOR *.FTN *.F77 *.F90

Java

*.java

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

The reason that .h extensions are mapped to C++ files rather than C files is because no information is lost and because it is common to use .h extensions in C++, where information would be lost if .h files were parsed with C rules.

OPTIONS

Despite the wealth of available options, defaults are set so that ctags is most commonly executed without any options (e.g. "ctags *"), which will create a tag file in the current directory for all known 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 only useful, when used together with etags or, equivalently, when ctags is run with the -e option. These options will be noted.

-a

Append the tags to an existing tag file. Equivalent to --append. [Ignored with -e]

-B

Use backward searching patterns (e.g. ?regexp?). [Ignored with -e]

-e

Output a tag file for use with Emacs. If this program is executed by the name etags, this option is enabled by default.

-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). [Ignored with -e]

-h list

Specifies a list of file extensions, separated by periods, which are to be interpreted as include, or header, files. This option affects how the scoping of tag types is interpreted (i.e. whether or not they are considered as globally visible or visible only within the file in which they are defined). Any tag type 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 tag type 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".

-i types

This option is similar to the --c-types option and is retained for compatibility with earlier versions. If types begins with the '=' character, it is equivalent to --c-types=types. Otherwise, it is equivalent to --c-types=+types. In addition, for backward compatibility, the following two additional modifiers are accepted:

F

An alternative for the --file-tags option.

S

An alternative for the --file-scope option.

-I tokenlist

Specifies a list of tokens 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 tokens listed are simple tokens, these tokens will be ignored during parsing of the source files. If a token is suffixed with a '+' character, ctags will also ignore any parenthesis-enclosed argument list which may immediately follow the token in the source files. If two tokens are separated with the '=' character, the first token is replaced by the second token for parsing purposes. The list of tokens may be supplied directly on the command line or read in from a separate file. If the first character of tokenlist is either a '.' or a pathname separator ('/' or '\\'), the parameter tokenlist will be interpreted as a filename from which to read a list of white-space delimited tokens (use "./filename" to specify a file found in the current directory). Otherwise, tokenlist is a list of tokens (or token 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.

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 BUGS, below). Some examples will illustrate this point.

int foo ARGDECL4(void *, ptr, long int, nbytes)
In the above example, the macro "ARGDECL2" would be mistakenly interpreted to be the name of the function instead of the correct name of "foo". Specifying -I ARGDECL2 results in the correct behavior.
/* creates an RCS version string in module */ MODULE_VERSION("$Revision: 8.1 $")
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(ddlexport)" 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.

-n

Equivalent to --excmd=number.

-N

Equivalent to --excmd=pattern.

-o tagfile

Equivalent to -f tagfile.

-p path

Use path as the default directory for each supplied source file (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. The supplied path is merely prepended to the each non-absolute source file name, adding any necessary path separator.

-R

Equivalent to --recurse=yes.

-u

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

-V

Enable verbose mode. This prints out a brief message describing what action is being taken for each file considered by ctags.

-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-types=f file), or generating a list of all externally visible global variables located in a source file (e.g. ctags -x --c-types=v --file-scope=no 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. This option is off by default.

--c-types=types

Specifies a list of C/C++ language tag types to include in the output file. The parameter types is a group of one-letter flags designating types of tags (listed below) to either include or exclude from the output. Each letter or group of letters may be preceded by either '+' (default, if omitted) to add it to the default set, or '-' to exclude it. In the absence of any preceding '+' or '-' sign, only those types explicitly listed in types will be included in the output. For example, to exclude macros but include prototypes, use --c-types=-m+p; to include only tags for functions, use --c-types=f. Tags for the following language constructs are supported (types are enabled by default except as noted):

c

classes

d

macro definitions (and #undef names)

e

enumerators

f

function definitions

g

enumeration names

m

class, struct, or union members

n

namespaces

p

function prototypes and declarations [off]

s

structure names

t

typedefs

u

union names

v

variable definitions

x

extern and forward variable declarations [off]

In addition to the above flags, the following one-letter modifiers are accepted:

A

Record the access of each member into the tag file. This information is recorded using an extension flag labeled "access".

C

Include an extra, class-qualified tag entry for each class member in the form "class::member". This allows locating class-qualified tags (e.g. ":tag class::member" in vi(1)). This is disabled by default because this could potentially more than double the size of the tag file.

--eiffel-types=types

Specifies a list of Eiffel language tag types to be included in the output. See --c-types for the definition of the format of types. Tags for the following Eiffel language constructs are supported (types are enabled by default except as noted):

c

classes

f

features

l

local entities [off]

--etags-include=file

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. [Used only with -e]

--excmd=type

Determines the type of EX command used to locate tags in the source file. [Ignored with -e]

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

number

Use only line numbers in the tag file for locating tags. This has four 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).

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.

--file-scope=yes|no

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.

--file-tags=yes|no

Indicates whether tags should be generated for source file names. This option is disabled by default.

--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. [Ignored with -e]

--fortran-types=types

Specifies a list of Fortran language tag types to be included in the output. See --c-types for the definition of the format of types. Tags for the following Fortran language constructs are supported (types are enabled by default except as noted):

b

block data

c

common blocks

e

entry points

f

functions

i

interfaces

l

labels [off]

m

modules

n

namelists

p

programs

s

subroutines

t

derived types

--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.

--java-types=types

Specifies a list of Java language tag types to be included in the output. See --c-types for the definition of the format of types. Tags for the following Java language constructs are supported (all are enabled by default):

c

classes

f

fields

i

interfaces

m

methods

p

packages

In addition to the above flags, the following one-letter modifiers are accepted:

A

Record the access of each field into the tag file. This information is recorded using an extension flag labeled "access".

C

Include an extra, class-qualified tag entry for each class member in the form "class.member". This allows locating class-qualified tags (e.g. ":tag class.member" in vi(1)). This is disabled by default because this could potentially more than double the size of the tag file.

--kind-long=yes|no

Specifies whether the identifier for the kind of the tag listed in extension flags of the tag file is a verbose name or a single letter. See the description of kind in EXTENSION FLAGS, below. When enabled, this will increase the size of the output by an average of about 5 characters per line or, roughly, 5%.

--lang=c|c++|eiffel|fortran|java

By default, ctags automatically selects the language of a source file according to its file name extension, ignoring those files whose extensions are unrecognized by ctags. This option forces the specified language to be used for every supplied file instead of automatically selecting the language based upon its extension.

--langmap=map(s)

Changes the mapping between file extensions and source languages (see SOURCE FILES, above). Each comma-separated map consists of the source language name, a colon, and a list of extensions separated by periods. If the first character in a map is a plus sign, then the extensions in the map will be appended to the current map; otherwise, the map will replace the current map.For example, to specify that only files with extensions of .c, .ec, and .xs are to be treated as C language files, use "--langmap=c:.c.ec.xs". To also specify that files with extensions of .j are to be treated as Java language files, use "--langmap=c:.c.ec.xs,java:+.j".

--line-directives=yes|no

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 --lang or --langmap option if the extension of the preprocessor output file is not known to ctags.

--links=yes|no

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

--recurse=yes|no

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. On Unix, directories named "SCCS" are skipped, because files in these directories are not source code, even though they have the same names as the source code to which they relate. Directories named "EIFGEN" are skipped, because these contain Eiffel compiler-generated C files. Also on Unix, 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.

--sort=yes|no

Indicates whether the tag file should be sorted on the tag name (default is yes). Note that the original vi(1) requires sorted tags. This option is on by default. [Ignored with -e]

--totals=yes|no

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

--version

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

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 (see EXTENSION FLAGS, below) embedded in an EX comment immediately appended to the EX command, which leaves it backwards 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.

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.

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.

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).

EXTENSION FLAGS

Extension flags are tab-separated key-value pairs appended to the end of the EX command as a comment, as described above in OPERATIONAL DETAILS. These key value pairs appear in the general form "key:value". The possible keys and the meaning of their values are as follows:

class

Indicates that this tag is a member of the class whose name is given by value.

enum

Indicates that this tag is a member of the enumeration whose name is given by value.

file

Indicates that the tag has a file-limited scope (i.e. is static to the file). This key has no corresponding value.

kind

Indicates the type of the tag. Its value is either one of the corresponding one-letter flags described under the various --<lang>-types options above, or a full name, depending upon the value of the --kind-long option. Alternatively, this key may be omitted, with only its value present (i.e. a field without a ':' defaults to the kind key).

interface

Indicates that this tag is a member of the interface whose name is given by value.

namespace

Indicates that this tag is a member of the namespace whose name is given by value.

private

Indicates the visibility of this class member is private. This key has no corresponding value.

protected

Indicates the visibility of this class member is protected. This key has no corresponding value.

public

Indicates the visibility of this class member is public. This key has no corresponding value.

struct

Indicates that this tag is a member of the structure whose name is given by value.

union

Indicates that this tag is a member of the union whose name is given by value.

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 (CAVEATS)

ctags has almost as many options as ls(1).

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 option.

Legacy C source code which uses C++ reserved keywords as variable or parameter names (e.g. "class", etc.) in a header file may fail to have correct tags generated for the objects using them. In order to properly handle such code, use the --lang option.

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 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.

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://darren hiebert com/ctags/index html

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>, <darren@hiwaay.net> http://darren.hiebert.com/

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. ''' $Id: cu.1,v 1.9 1995/08/02 00:16:58 ian Rel $

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