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9.6 Variables used when building a program

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:

AM_CPPFLAGS
The contents of this variable 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_HEADERS or AM_CONFIG_HEADER). You can disable the default `-I' options using the `nostdinc' option.

AM_CPPFLAGS is ignored in preference to a per-executable (or per-library) _CPPFLAGS variable if it is defined.

INCLUDES
This does the same job as `AM_CPPFLAGS'. It is an older name for the same functionality. This variable is deprecated; we suggest using `AM_CPPFLAGS' instead.

AM_CFLAGS
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.

COMPILE
This is the command used to actually compile a C source file. The filename is appended to form the complete command line.

AM_LDFLAGS
This is the variable which the `Makefile.am' author can use to pass in additional linker flags. In some situations, this is not used, in preference to the per-executable (or per-library) _LDFLAGS.

LINK
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.


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