–Dname[=def]

Defines symbol name to the preprocessor.

–E

Runs only the preprocessor on the C++ source files and sends result to stdout. Does not compile.

-H

Prints path names of included files. 

–P

Only preprocesses source; outputs to .i file.

–Uname

Deletes initial definition of preprocessor symbol name.

–xM

Outputs makefile dependency information. 

–xM1

Generates dependency information, but excludes /usr/include.