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CTAGS(1) CTAGS(1) NAME ctags - Generate C and C++ language tag files for use with vi(1) SYNOPSIS ctags [-aBeFnNRux] [-f tagfile] [-h list] [-i types] [-I ignorelist] [-L listfile] [-p path] [-o tagfile] [--append] [--excmd=m|n|p] [--format=level] [--help] [--if0] [--lang=c|c++|java] [--langmap=map(s)] [--recurse] [--sort] [--totals] [--version] [file(s)] etags [-aRx] [-f tagfile] [-h list] [-i types] [-I ignorelist] [-L listfile] [-p path] [-o tagfile] [--append] [--help] [--if0] [--lang=c|c++|java] [--langmap=map(s)] [--recurse] [--totals] [--ver- sion] [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++ and Java language objects found in file(s) that allows these items to be quickly and easily located by a text editor or other util- ity. 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 (some are optional): macro definitions (names created by #define) enumerators (values inside an enumeration) function (method) definitions class, enum, struct, and union names interface names (Java) namespace names (C++) typedefs Darren Hiebert Version 2.3 1 CTAGS(1) CTAGS(1) variables (definitions and extern declarations) function prototypes and declarations data members 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. SOURCE FILES Unless the --lang option is specified, the language of each source file is automatically selected based upon its file extension, according to the following default map- ping. C *.c C++ *.C, *.c++, *.cc, *.cpp, *.cxx and any file considered a header file according to the -h option. Java *.java All other files extensions are ignored. This permits run- ning 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. This default mapping of file extensions to source language may be changed by using the --langmap option. Automatic selec- tion of the source language may be disabled by using the --lang option. 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 the specified files. The options described below are provided merely to allow custom tai- loring 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 Darren Hiebert Version 2.3 2 CTAGS(1) CTAGS(1) 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 periods. This option affects how the scoping of tag types is interpreted (i.e. whether or not they are considered as static). All tag types other than functions (methods) and variables are con- sidered static when they appear in a non-header file (since they cannot be seen outside of that file) and non-static when they appear in a header file (since they can be seen in other files wherever that header file is included). See also the S modifier of the -i option. 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 one-letter flags 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 Darren Hiebert Version 2.3 3 CTAGS(1) CTAGS(1) language contructs are supported (default settings are on except as noted): c class names d macro definitions e enumerators f function (or method) definitions g enumeration names i interface names (Java only) m data members [off] i namespace names (C++ only) p function prototypes and declarations [off] s structure names t typedefs u union names v variable definitions x extern variable declarations [off] In addition to the above flags, the following one- letter modifiers are accepted: C For C++ and Java, include an extra, class- qualified tag entry for each class member (function/method and data) in the form "class::member" (C++) or "class.member" (Java). 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. 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)). This is disabled by default. 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, and non-static when they appear in a header file. See also the -h option. This is enabled by default. The default value for types is "=cdefgintuvCS". -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 Darren Hiebert Version 2.3 4 CTAGS(1) CTAGS(1) 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: 6.10 $") 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 each supplied source file (whether supplied on the command line or in a file specified with the -L option), unless the Darren Hiebert Version 2.3 5 CTAGS(1) CTAGS(1) 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. -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: -aBefFno, 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, Darren Hiebert Version 2.3 6 CTAGS(1) CTAGS(1) below). However, this option has one significant drawback: changes to the source files can cause the line numbers recorded in the tag file to no longer correspond to the lines in the source file, causing jumps to some tags to miss the target definition by one or more lines. Basically, this option is best used when the source code to which it is applied is not subject to change. Selecting this option type causes the following options to be ignored: -BF. pattern Uses EX search patterns for all tags, rather than the line numbers usually used for macro definitions. This has the advantage of not referencing obsolete line numbers when lines have been added or removed since the tag file was generated. mixed Uses line numbers for macro definition tags and EX patterns for everything else. This is the default format generated by the original ctags and is, therefore, retained as the default for this option. --format=level Change the format of the output tag file. Currently the only valid values for level are 1 or 2. Level 1 specifies the original tag file format and level 2 specifies a new extended format containing extension flags (but in a manner which retains backward 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 Darren Hiebert Version 2.3 7 CTAGS(1) CTAGS(1) off by default. --lang=c|c++|java By default, ctags automatically selects the language of a source file according to its file name exten- sion, ignoring those files whose extensions are unknown to ctags. This option forces the specified language to be used for every supplied file, instead of keying off of their extensions. --langmap=map(s) Overrides the default mapping between source language and file extension. Each comma-separated map consists of the source language name, a colon, and a list of extensions separated by periods. For example, to specify that 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 lan- guage files, use "--langmap=c:.c.ec.xs,java:.java.j". --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 they relate to. Also on Unix, sym- bolic links are followed; if you don't like this, 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. If the parameter is omit- ted, =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. Darren Hiebert Version 2.3 8 CTAGS(1) CTAGS(1) --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 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 (see EXTENSION FLAGS, below) embedded in an EX comment immediately appended to the EX command, which leaves it backwards compati- ble with original vi(1) implemenations. 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 Darren Hiebert Version 2.3 9 CTAGS(1) CTAGS(1) 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. C++ operator definitions are specially handled. In the case of operators beginning with a non-identifer character (e.g. "operator ="), the name of the tag added to the tag file will be the operator prefixed by "operator", with no intervening white space (e.g. "operator="). In the case of operators beginning with identifer characters (e.g. "oper- ator new"), the name of the tag added to the tag file will be simply the name of the operator, without a prefix (e.g. "new"). After creating or appending to the tag file, it is sorted Darren Hiebert Version 2.3 10 CTAGS(1) CTAGS(1) 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). 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 one of the corresponding one-letter flags described under the -i option, above. Alterna- tively, this key may be omitted, with only the value present (i.e. a field without a 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. Darren Hiebert Version 2.3 11 CTAGS(1) CTAGS(1) 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 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. Darren Hiebert Version 2.3 12 CTAGS(1) CTAGS(1) :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 definitions of objects within a function will not have tags generated for them. 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) Darren Hiebert Version 2.3 13 CTAGS(1) CTAGS(1) 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. 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://darren.hiebert.com/ctags/index.html 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: Darren Hiebert Version 2.3 14 CTAGS(1) CTAGS(1) 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 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 <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. Darren Hiebert Version 2.3 15