Re: -M option for g++?

[Paul Pluzhnikov]

durkman@gmail.com writes:

> Can someone point me to a page that explains the -M options for g++? I
> cannot find -M options in the man page of g++

Try "info gcc" instead:

`-M'
     Instead of outputting the result of preprocessing, output a rule
     suitable for `make' describing the dependencies of the main source
     file.  The preprocessor outputs one `make' rule containing the
     object file name for that source file, a colon, and the names of
     all the included files, including those coming from `-include' or
     `-imacros' command line options.

     Unless specified explicitly (with `-MT' or `-MQ'), the object file
     name consists of the basename of the source file with any suffix
     replaced with object file suffix.  If there are many included
     files then the rule is split into several lines using `\'-newline.
     The rule has no commands.

     This option does not suppress the preprocessor's debug output,
     such as `-dM'.  To avoid mixing such debug output with the
     dependency rules you should explicitly specify the dependency
     output file with `-MF', or use an environment variable like
     `DEPENDENCIES_OUTPUT' (*note Environment Variables::).  Debug
     output will still be sent to the regular output stream as normal.

     Passing `-M' to the driver implies `-E', and suppresses warnings
     with an implicit `-w'.

`-MM'
     Like `-M' but do not mention header files that are found in system
     header directories, nor header files that are included, directly
     or indirectly, from such a header.

     This implies that the choice of angle brackets or double quotes in
     an `#include' directive does not in itself determine whether that
     header will appear in `-MM' dependency output.  This is a slight
     change in semantics from GCC versions 3.0 and earlier.

`-MF FILE'
     When used with `-M' or `-MM', specifies a file to write the
     dependencies to.  If no `-MF' switch is given the preprocessor
     sends the rules to the same place it would have sent preprocessed
     output.

     When used with the driver options `-MD' or `-MMD', `-MF' overrides
     the default dependency output file.

`-MG'
     In conjunction with an option such as `-M' requesting dependency
     generation, `-MG' assumes missing header files are generated files
     and adds them to the dependency list without raising an error.
     The dependency filename is taken directly from the `#include'
     directive without prepending any path.  `-MG' also suppresses
     preprocessed output, as a missing header file renders this useless.

     This feature is used in automatic updating of makefiles.

`-MP'
     This option instructs CPP to add a phony target for each dependency
     other than the main file, causing each to depend on nothing.  These
     dummy rules work around errors `make' gives if you remove header
     files without updating the `Makefile' to match.

     This is typical output:

          test.o: test.c test.h
          
          test.h:

`-MT TARGET'
     Change the target of the rule emitted by dependency generation.  By
     default CPP takes the name of the main input file, including any
     path, deletes any file suffix such as `.c', and appends the
     platform's usual object suffix.  The result is the target.

     An `-MT' option will set the target to be exactly the string you
     specify.  If you want multiple targets, you can specify them as a
     single argument to `-MT', or use multiple `-MT' options.

     For example, `-MT '$(objpfx)foo.o'' might give

          $(objpfx)foo.o: foo.c

`-MQ TARGET'
     Same as `-MT', but it quotes any characters which are special to
     Make.  `-MQ '$(objpfx)foo.o'' gives

          $$(objpfx)foo.o: foo.c

     The default target is automatically quoted, as if it were given
     with `-MQ'.

`-MD'
     `-MD' is equivalent to `-M -MF FILE', except that `-E' is not
     implied.  The driver determines FILE based on whether an `-o'
     option is given.  If it is, the driver uses its argument but with
     a suffix of `.d', otherwise it take the basename of the input file
     and applies a `.d' suffix.

     If `-MD' is used in conjunction with `-E', any `-o' switch is
     understood to specify the dependency output file (but *note
     -MF::), but if used without `-E', each `-o' is understood to
     specify a target object file.

     Since `-E' is not implied, `-MD' can be used to generate a
     dependency output file as a side-effect of the compilation process.

`-MMD'
     Like `-MD' except mention only user header files, not system
     -header files.


Cheers,
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