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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 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.

INCLUDES ¶

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.

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.