A.13 AC_PROG_FPP

AC_PROG_FPP(required-features,[FPP-SRC-EXT=F])

required-features is a space-separated list of features that the Fortran preprocessor must have for the code to compile. It is up to the package maintainer to properly set these requirements.

FPP-SRC-EXT is an optional specification of the file extension for preprocessable Fortran source files (without a leading dot). It defaults to F: There would appear to be a problem, here, with case-insensitive filesystems, such as the default HFS+ on MacOS X, and Windows filesystems, since the extension .F is indistinguishable from plain .f. However there is no problem in practice, since the Fortran compilers you are likely to encounter on these platforms are all capable of compiling preprocessable Fortran directly to object code, without requiring the intermediate .f file (and there is a check in autoconf to double-check that this is true).

The macro works out if the Fortran compiler discovered by macro AC_PROG_FC has the requested set of features. If so, it arranges for the compilation to be done `directly'; if not, it arranges for `indirect' compilation, where the preprocessable Fortran code is converted to pure Fortran code and only subsequently passed to the Fortran compiler.

The configure variables which this macro sets, and which are available for substitution, are as follows.

FPP

The Fortran preprocessor which the macro decides is suitable.

FPPFLAGS

The flags which will be given to the compiler (in direct mode) or preprocessor (in indirect mode).

FPP_SRC_EXT

This is the file extension (without a dot) of preprocessable Fortran files; by default this is `F'.

FPP_COMPILE_EXT

This contains the file extension which the Fortran compiler will accept. It is the same as FPP_SRC_EXT if the compiler itself can do preprocessing (`direct' compilation), or a dummy value (not .f, since that would conflict with the pre-existing rule for compiling Fortran) if it cannot, and the file must be preprocessed separately (`indirect').

FPP_PREPROCESS_EXT

The partner of FPP_COMPILE_EXT. This is FPP_SRC_EXT for indirect compilation, or a dummy value for direct compilation, when the corresponding separate-processing generated rule should be ignored.

FPP_MAKE_FLAGS

This is used to pass flags to the cpp or fpp command if we compile directly, and leave them out otherwise.

FPP_OUTPUT

This is used to redirect FPP output to the .f file in those cases where FPP writes to stdout rather than to a file: it is either blank or something like >$@

file.f: file.$(FPP_SRC_EXT)
        $(FPP) $(FPPFLAGS) $(CPPFLAGS) file.$(FPP_SRC_EXT) $(FPP_OUTPUT)

NOTE: There are some features of this macro support which are arguably bad autoconf style, and it is very likely that this macro will change. The documentation below is only for completeness, and you are advised not to pay any attention to it. See Appendix C.

Supported features are:

include

the preprocessor must correctly process #include directives and -I options

define

correctly process -D options

substitute

substitute macros in Fortran code (some preprocessors touch only lines starting with #)

wrap

wrap lines that become too long through macro substitution. fpp is probably the only preprocessor that does this.

cstyle

Do not suppress C style comments (the -C option in cpp)

CSTYLE

Do suppress C style comments (e.g. code contains C-style comments, and compiler may not know how to handle them)

Features can be abbreviated: i, in, inc etc. are equivalent to include. Features can be deselected (feature not needed) by prepending "no", e.g. nodef (=nodefine), now (=nowrap).

Default for the feature list is [include define substitute nowrap nocstyle noCSTYLE]

Feature requirements corresponding to the defaults may be omitted

Note that "wrap" implies "substitute", and CSTYLE and cstyle cannot be requested at the same time. The macro adjusts this automatically.