DEHEADER(1) Development Tools DEHEADER(1)NAMEdeheader - report which includes in C or C++ compiles can be removed
SYNOPSISdeheader [-h] [-m command] [-i pattern] [-q] [-r] [-v] [-x pattern]
[-V] [file-or-dir]
DESCRIPTION
This tool takes a list of C or C++ sourcefiles and generates a report
on which #includes can be omitted from them; also, what standard
inclusions may be required for portability. The test, for each foo.c or
foo.cc or foo.cpp, is simply whether 'rm foo.o; make foo.o' returns a
zero status (but the build command may be overridden).
Optionally, with the -r switch, the unneeded headers are removed from
the sourcefiles. Don't use this option unless you have your sourcefiles
safely under version control and can revert!
If a sourcefile argument is a directory, the report is generated on all
source files beneath it. Subdirectories beginning with a dot are
assumed to be repository directories for version-control systems and
ignored. If no arguments are given, the program runs as if the name of
the current directory had been passed to it.
Inclusions within the scope of #if/#ifdef/#else/#endif directives are
left alone, because trying to reason about potential combinations of -D
and U options would be too complicated and prone to weird errors. One
exception: headers protected only by S_SPLINT_S, the conditional for
blocking scanning by the static analysis tool splint(1), are scanned
normally.
The tool will also emit warnings about duplicate inclusions, and
inclusions required for portability but not present.
It is recommended that you arrange to compile with options that will
stop the compiler on warnings when using this tool; otherwise it will
report headers that only declare prototypes and return types (and thus
throw only warnings) as being not required. Under gcc the compiler
options to accomplish this are -Werror -Wfatal-errors. If your makefile
follows normal conventions, running with -m "make CFLAGS='-Werror
-Wfatal-errors'" may do the right thing; you can check this by running
with -v -v -v to see what compilation commands are actually emitted.
On each test compile, the original sourcefile is moved to a name with
an .orig suffix and restored on interrupt or after processing with its
original timestamp, unless the -r option was given and headers removed.
At verbosity level 0, only messages indicating removable headers are
issued. At verbosity 1, test compilations are timed and progess
indicated with a twirling-baton prompt. At verbosity level 2, you get
verbose progress messages on the analysis. At verbosity level 3, you
see the output from the make and compilation commands.
If the -q (--quiet) option flag was not set, the last line of the
output will be a statistical summary.
Running deheader will leave a lot of binaries in your directory that
were compiled in ways possibly not invoked by your normal build
process. Running "make clean" afterwards (or the equivalent under
whatever build system you are using) is strongly recommended.
OPTIONS-h
Display some help and exit.
-m
Set the build command used for test compiles. Defaults to 'make'.
-i
Set a pattern for includes to be ignored. Takes a Python regular
expression.
-q
Suppress statistical summary.
-r
Remove header inclusions from sourcefiles where they are not
required.
-v
Set verbosity.
-x
Exclude files with names matching the specified Python regexp.
-V
Show version of program and exit.
BUGS
Very rarely, test-compiling after running with -r may show that this
tool removed some headers that are actually required for your build.
This can happen because deheader doesn't know about all the strange
things your build system gets up to, and the problem of analyzing your
build to understand them would be Turing-complete. Simply revert the
altered files and continue.
Due to minor variations in system headers, it is possible your program
may not port correctly to other Unix variants after being deheadered.
This is normally not a problem with the portion of the API specified by
POSIX and ANSI C, but may be for headers that are not standardized or
only weakly standardized. The sockets API (sys/select.h, sys/sockets.h,
and friends such as sys/types.h and sys.stat.h) is perhaps the most
serious trouble spot. deheader has an internal table of rules that
heads off the most common problems by suppressing deletion of headers
that are required for portability, but your mileage may vary.
Sufficiently perverse C++ can silently invalidate the brute-force
algorithm this tool uses. Example: if an overloaded function has
different overloads from two different files, removing one may expose
the other, changing runtime semantics without a compile-time warning.
Similarly, removing a later file containing a template specialization
may lead to undefined behavior from a template defined in an earlier
file. Use this with caution near such features, and test carefully.
AUTHOR
Eric S. Raymond <esr@snark.thyrsus.com>; (home page at
http://www.catb.org/~esr/).
deheader 06/03/2014 DEHEADER(1)
