Sometimes it is convenient to put version identification strings directly into working files. Certain special strings called version headers are replaced in each successive version by the number of that version.
If you are using RCS, and version headers are present in your working files, Emacs can use them to determine the current version and the locking state of the files. This is more reliable than referring to the master files, which is done when there are no version headers. Note that in a multi-branch environment, version headers are necessary to make VC behave correctly (see section Multi-User Branching).
Searching for version headers is controlled by the variable
vc-consult-headers. If it is non-nil, Emacs searches for
headers to determine the version number you are editing. Setting it to
nil disables this feature.
You can use the C-x v h command (vc-insert-headers) to
insert a suitable header string.
The default header string is `$Id$' for RCS and
`%W%' for SCCS. You can specify other headers to insert by
setting the variable vc-header-alist. Its value is a list of
elements of the form (program . string) where
program is RCS or SCCS and string is the
string to use.
Instead of a single string, you can specify a list of strings; then each string in the list is inserted as a separate header on a line of its own.
It is often necessary to use "superfluous" backslashes when writing the strings that you put in this variable. This is to prevent the string in the constant from being interpreted as a header itself if the Emacs Lisp file containing it is maintained with version control.
Each header is inserted surrounded by tabs, inside comment delimiters,
on a new line at the start of the buffer. Normally the ordinary comment
start and comment end strings of the current mode are used, but for
certain modes, there are special comment delimiters for this purpose;
the variable vc-comment-alist specifies them. Each element of
this list has the form (mode starter ender).
The variable vc-static-header-alist specifies further strings
to add based on the name of the buffer. Its value should be a list of
elements of the form (regexp . format). Whenever
regexp matches the buffer name, format is inserted as part
of the header. A header line is inserted for each element that matches
the buffer name, and for each string specified by
vc-header-alist. The header line is made by processing the
string from vc-header-alist with the format taken from the
element. The default value for vc-static-header-alist is as follows:
(("\\.c$" .
"\n#ifndef lint\nstatic char vcid[] = \"\%s\";\n\
#endif /* lint */\n"))
It specifies insertion of text of this form:
#ifndef lint static char vcid[] = "string"; #endif /* lint */
Note that the text above starts with a blank line.
If you use more than one version header in a file, put them close
together in the file. The mechanism in revert-buffer that
preserves markers may not handle markers positioned between two version
headers.
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