Occasionally it is useful to know which Makefile variables Automake uses for compilations; for instance you might need to do your own compilation in some special cases.
Some variables are inherited from Autoconf; these are CC, CFLAGS, CPPFLAGS, DEFS, LDFLAGS, and LIBS. There are some additional variables which Automake itself defines:
The contents of this macro are passed to every compilation which invokes the C preprocessor; it is a list of arguments to the preprocessor. For instance, -I and -D options should be listed here.
Automake already provides some -I options automatically. In particular it generates -I$(srcdir), -I., and a -I pointing to the directory holding config.h (if you've used AC_CONFIG_HEADER or AM_CONFIG_HEADER). You can disable the default -I options using the nostdinc option.
This does the same job as AM_CPPFLAGS. It is an older name for the same functionality. This macro is deprecated; we suggest using AM_CPPFLAGS instead.
This is the variable which the Makefile.am author can use to pass in additional C compiler flags. It is more fully documented elsewhere. In some situations, this is not used, in preference to the per-executable (or per-library) CFLAGS.
This is the command used to actually compile a C source file. The filename is appended to form the complete command line.
This is the command used to actually link a C program. It already includes -o $@ and the usual variable references (for instance, CFLAGS); it takes as "arguments" the names of the object files and libraries to link in.