CTAGS

NAME

SYNOPSIS

ctags

[ -aBdFnsStTuwWx ] [ -f tagfile ] [ -h list ]
[ -i types ] [ -L listfile ] [ -o tagfile ]
[ --help ] [ file(s) ]

DESCRIPTION

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 language files.

Tag index files are supported by the vi(1) editor and its derivatives (such as vim, elvis, stevie, and xvi) through the use of the ":ta" command, which locates the object associated with a name appearing in a source file and jumps to the file and line which defines the name. The following types of tags are supported by ctags:

macro definitions (i.e. names created by #define)
enumerated values (i.e. the values inside enum{...})
function definitions
function prototypes or declarations (optional)
class, enum, struct and union tags
typedefs
variables

With the exception of macro definitions, only objects defined outside of function, class, structure and union blocks are candidates for a tag. For every one of the selected objects listed above which are discovered in the source files supplied to ctags, a separate line is added to the tags file in the following format:

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.

a search pattern (either /pattern/ or ?pattern?) or line number with which to locate the tag within the file

Note that, unless changed via -n, line number are only used for tags for macro definitions, while patterns are used for all other tags.

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 STORE_SEPARATELY
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 is detected within a #if conditional.

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 (*fptr) __ARGS((int one, char two));

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

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

OPTIONS

Note that spaces separating options from their parameters are optional.

-a

Append the tags to an existing tag file.

-B

Use backward searching patterns (?...?).

-d

Include macro definitions in the output file. This is equivalent to -i+d and is supported only for backwards compatibility with other versions of ctags. Use of -i is preferred.

-f tagfile

Output tags to the specified file (default is "tags"). 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 -o *.c", which would otherwise overwrite your first C file with the tags generated by the rest!

-F

Use forward searching patterns (/.../) (default).

-h list

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

-i types

Specifies the list of tag types to include in the output file. Types is a group of letters designating the types of tags affected. Each letter or group of letters may be preceded by either a '+' sign (default, if omitted) to add it to those already included, a '-' sign to exclude it from the list (e.g. to exclude a default tag type), or an '=' sign to include its corresponding tag type at the exclusion of those not listed. The following tag types are supported:

d

macro definitions

e

enumerated values (values inside enum{...})

f

function and method definitions

g

enum/struct/union tags (or new C++ types)

p

external function prototypes

t

typedefs

v

variable declarations

In addition, the following two modifiers are accepted:

P

Prefix static tags (if included) in the tag file with the filename in which they appear, followed by a colon (Elvis style; not widely supported).

S

Include static tags (those not visible outside of a single source file). Function and variable definitions are considered static only when their definitions are preceded with the "static" keyword. All other types of tags are considered static when they appear in a non-header file (see the -h option).

The default value of list is "=defgtvS" (i.e all tag types except for function prototypes; include static tags but do not prefix them).

-L listfile

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

-n

Places places the line numbers in the source file where tags are located rather than patterns to be searched for. This has two advantages:

1.

Significantly reduces the size of the resulting tag file.

2.

Eliminates failures to find tags because the line defining the tag has changed, causing the pattern match to fail (note that some editors, such as vim, are able to recover in many such instances).

3.

Eliminates finding identical matching, but incorrect, source lines (see BUGS, below).

However, this option has one significant drawback: changes to the source files can cause the line numbers recorded in the tag file to no longer correspond to the lines in the source file, causing jumps to some tags to miss the target definition by one or more lines. Selecting this option causes the following options to be ignored: -F and -B.

-o tagfile

Alternative for -f.

-s

Include static tags in the output file, each prefixed with the name of the file in which it appears followed by a colon. This is equivalent to -i+SP and is supported only for backwards compatibility with other versions of ctags. Use of -i is preferred.

-S

Include static tags in the output file, but do not prefix them, thereby making them appear the same as global tags. This is equivalent to -i+S-P and is supported only for backwards compatibility with other versions of ctags. Use of -i is preferred.

-t

Include typedefs in the output file. This is equivalent to -i+t and is supported only for backwards compatibility with other versions of ctags. Use of -i is preferred.

-T

Include typedefs and class/enum/struct/union tags in the output file. This is equivalent to -i+tg and is supported only for backwards compatibility with other versions of ctags. Use of -i is preferred.

-u

Unsorted; do not sort the tags. Please note that this disables the warning messages normally enabled by -W, because sorted tags are used to detect duplicate tags. Note also that vi(1) requires sorted tags.

-w

Exclude warnings about duplicate tags (default).

-W

Generate warnings about duplicate tags.

-x

Print a tabular, human-readable cross reference (xref) file to standard output. The information contained in the output includes: the tag name; the tag type; 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: -a, -f, -i+P, -n, -o, -B and -F. 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).

--help

Prints to standard output a detailed usage description.

ENVIRONMENT VARIABLES

CTAGS

If found, this variable 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.

HOW TO USE WITH VI

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).

BUGS

Because ctags does not presently look inside brace enclosed blocks, nested declarations for class/enum/struct/union tags and enumeration values (i.e. declared within another class, structure or union) will not have tags generated for them.

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

int variable;

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

/* ... */

}

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

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

#ifdef GLOBAL
#define EXTERN
#define INIT(assign)   assign

#else
#define EXTERN extern
#define INIT(assign)
#endif

EXTERN BUF *firstbuf INIT(= NULL);

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

FILES

tags

The default tag file created by ctags.

SEE ALSO

http://fly.hiwaay.net/~darren/ctags.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.math.fu-berlin.de/~guckes/vim/

AUTHOR

MOTIVATION

"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

Credit is also due Bram Moolenaar, 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.

Index

NAME

SYNOPSIS

DESCRIPTION

OPTIONS

ENVIRONMENT VARIABLES

HOW TO USE WITH VI

BUGS

FILES

SEE ALSO

AUTHOR

MOTIVATION

CREDITS