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Associated with each program are a collection of variables which can be used to modify how that program is built. There is a similar list of such variables for each library. The canonical name of the program (or library) is used as a base for naming these variables.
In the list below, we use the name “maude” to refer to the program or library. In your Makefile.am you would replace this with the canonical name of your program. This list also refers to “maude” as a program, but in general the same rules apply for both static and dynamic libraries; the documentation below notes situations where programs and libraries differ.
This variable, if it exists, lists all the source files which are compiled to build the program. These files are added to the distribution by default. When building the program, Automake will cause each source file to be compiled to a single .o file (or .lo when using libtool). Normally these object files are named after the source file, but other factors can change this. If a file in the ‘_SOURCES’ variable has an unrecognized extension, Automake will do one of two things with it. If a suffix rule exists for turning files with the unrecognized extension into .o files, then automake will treat this file as it will any other source file (see Support for Other Languages). Otherwise, the file will be ignored as though it were a header file.
The prefixes ‘dist_’ and ‘nodist_’ can be used to control whether files listed in a ‘_SOURCES’ variable are distributed. ‘dist_’ is redundant, as sources are distributed by default, but it can be specified for clarity if desired.
It is possible to have both ‘dist_’ and ‘nodist_’ variants of a given ‘_SOURCES’ variable at once; this lets you easily distribute some files and not others, for instance:
nodist_maude_SOURCES = nodist.c dist_maude_SOURCES = dist-me.c
By default the output file (on Unix systems, the .o file) will be
put into the current build directory. However, if the option
subdir-objects is in effect in the current directory then the
.o file will be put into the subdirectory named after the source
file. For instance, with subdir-objects enabled,
sub/dir/file.c will be compiled to sub/dir/file.o. Some
people prefer this mode of operation. You can specify
subdir-objects in AUTOMAKE_OPTIONS (see Changing Automake’s Behavior).
Automake needs to know the list of files you intend to compile statically. For one thing, this is the only way Automake has of knowing what sort of language support a given Makefile.in requires. 5 This means that, for example, you can’t put a configure substitution like ‘@my_sources@’ into a ‘_SOURCES’ variable. If you intend to conditionally compile source files and use configure to substitute the appropriate object names into, e.g., ‘_LDADD’ (see below), then you should list the corresponding source files in the ‘EXTRA_’ variable.
This variable also supports ‘dist_’ and ‘nodist_’ prefixes, e.g., ‘nodist_EXTRA_maude_SOURCES’.
A static library is created by default by invoking $(AR)
$(ARFLAGS) followed by the name of the library and then the objects
being put into the library. You can override this by setting the
‘_AR’ variable. This is usually used with C++; some C++
compilers require a special invocation in order to instantiate all the
templates which should go into a library. For instance, the SGI C++
compiler likes this variable set like so:
libmaude_a_AR = $(CXX) -ar -o
Extra objects can be added to a library using the ‘_LIBADD’
variable. For instance this should be used for objects determined by
configure (see Building a library).
Extra objects can be added to a program by listing them in the
‘_LDADD’ variable. For instance this should be used for objects
determined by configure (see Linking the program).
‘_LDADD’ and ‘_LIBADD’ are inappropriate for passing program-specific linker flags (except for ‘-l’, ‘-L’, ‘-dlopen’ and ‘-dlpreopen’). Use the ‘_LDFLAGS’ variable for this purpose.
For instance, if your configure.ac uses AC_PATH_XTRA, you
could link your program against the X libraries like so:
maude_LDADD = $(X_PRE_LIBS) $(X_LIBS) $(X_EXTRA_LIBS)
This variable is used to pass extra flags to the link step of a program or a shared library.
It is also occasionally useful to have a program depend on some other target which is not actually part of that program. This can be done using the ‘_DEPENDENCIES’ variable. Each program depends on the contents of such a variable, but no further interpretation is done.
If ‘_DEPENDENCIES’ is not supplied, it is computed by Automake. The automatically-assigned value is the contents of ‘_LDADD’ or ‘_LIBADD’, with most configure substitutions, ‘-l’, ‘-L’, ‘-dlopen’ and ‘-dlpreopen’ options removed. The configure substitutions that are left in are only ‘$(LIBOBJS)’ and ‘$(ALLOCA)’; these are left because it is known that they will not cause an invalid value for ‘_DEPENDENCIES’ to be generated.
You can override the linker on a per-program basis. By default the linker is chosen according to the languages used by the program. For instance, a program that includes C++ source code would use the C++ compiler to link. The ‘_LINK’ variable must hold the name of a command which can be passed all the .o file names as arguments. Note that the name of the underlying program is not passed to ‘_LINK’; typically one uses ‘$@’:
maude_LINK = $(CCLD) -magic -o $@
Automake allows you to set compilation flags on a per-program (or per-library) basis. A single source file can be included in several programs, and it will potentially be compiled with different flags for each program. This works for any language directly supported by Automake. These per-target compilation flags are ‘_CCASFLAGS’, ‘_CFLAGS’, ‘_CPPFLAGS’, ‘_CXXFLAGS’, ‘_FFLAGS’, ‘_GCJFLAGS’, ‘_LFLAGS’, ‘_OBJCFLAGS’, ‘_RFLAGS’, and ‘_YFLAGS’.
When using a per-target compilation flag, Automake will choose a different name for the intermediate object files. Ordinarily a file like sample.c will be compiled to produce sample.o. However, if the program’s ‘_CFLAGS’ variable is set, then the object file will be named, for instance, maude-sample.o. (See also Why are object files sometimes renamed?.)
In compilations with per-target flags, the ordinary ‘AM_’ form of the flags variable is not automatically included in the compilation (however, the user form of the variable is included). So for instance, if you want the hypothetical maude compilations to also use the value of ‘AM_CFLAGS’, you would need to write:
maude_CFLAGS = … your flags … $(AM_CFLAGS)
On some platforms the allowable file names are very short. In order to support these systems and per-target compilation flags at the same time, Automake allows you to set a “short name” which will influence how intermediate object files are named. For instance, in the following example,
bin_PROGRAMS = maude maude_CPPFLAGS = -DSOMEFLAG maude_SHORTNAME = m maude_SOURCES = sample.c …
the object file would be named m-sample.o rather than maude-sample.o.
This facility is rarely needed in practice, and we recommend avoiding it until you find it is required.
Next: Default _SOURCES, Previous: Building a Shared Library, Up: Building Programs and Libraries [Contents][Index]