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This section contains detailed information on how to use project files most effectively, and how to avoid some pitfalls.

One can divide the checks ftnchek does into two categories, local and global. Local checking is restricted to within a single routine, and catches things like uninitialized variables, unintended loss of precision in arithmetic expressions, etc. This sort of checking can be done on each subprogram independently. Furthermore, local checking of a subprogram does not need to be repeated when some other subprogram is changed. Global checking catches things like calling a subroutine with the wrong argument types, or disagreeing in common block declarations. It requires looking at the whole set of subprograms interacting with each other.

The purpose of project files is to allow the local checking and global checking steps to be separated. Assuming that each subprogram is in its own source file, you can run ftnchek once on each one to do local checking while suppressing global checking. Then ftnchek can be run once on all the project files together to do the global checking. The sample makefile below shows how to automate this task. The ``.f.prj'' target updates a project file for a particular file any time the source file changes. The information needed for global checking is saved in the project file. The ``check'' target does the combined global checking. Typically ``make check'' would repeat the ``ftnchek -project'' step only on changed source files, then do the global check. This is obviously a big advantage for large programs, when many subprograms seldom if ever change.

It is best when using project files to place each subprogram in a separate source file. If each source file may contain more than one subprogram, it complicates the definition of ``local'' and ``global'' checking because there is some inter-module checking that is contained within a file. ftnchek tries to do the right thing in this case, but there are some complications (described below) due to the trade-off between avoiding re-doing cross-checks and preserving information about the program's structure.

Ordinarily, to do the least amount of re-checking, project files should be created with the -library flag in effect and trimming turned on. In this mode, the information saved in the project file consists of all subprogram declarations, all subprogram invocations not resolved by declarations in the same file, and one instance of each COMMON block declaration. This is the minimum amount of information needed to check agreement between files.

If the source file contains more than one routine, there are some possible problems that can arise from creating the project file in library mode, because the calling hierarchy among routines defined within the file is lost. Also, if the routines in the file make use of COMMON blocks that are shared with routines in other files, there will not be enough information saved for the correct checking of set and used status of COMMON blocks and COMMON variables according to the -usage setting. Therefore if you plan to use project files when -usage checking is turned on (which is the default situation), and if multiple routines in one project file share COMMON blocks with routines in other files, the project files should be created with the -library flag turned off. In this mode, ftnchek saves, besides the information listed above, one invocation of each subprogram by any other subprogram in the same file, and all COMMON block declarations. This means that the project file will be larger than necessary, and that when it is read in, ftnchek may repeat some inter-module checks that it already did when the project file was created. If each project file contains only one module, there is no loss of information in creating the project files in library mode.

Because of the possible loss of information entailed by creating a project file with the -library flag in effect, whenever that project file is read in later, it will be treated as a library file regardless of the current setting of the -library flag. On the other hand, a project file created with library mode turned off can be read in later in either mode.

The foregoing discussion assumes that the trimming options of the -project setting are turned on when the project file is created. This is the normal situation. The no-trim options of the -project setting are provided in case one wants to use the project files for purposes other than checking the program with ftnchek. For instance, one could write a Perl script to analyze the project files for information about how the different subprograms are called. You should not use the no-trim options to deal with the issues of information loss discussed above, since they cause more information than necessary to be stored. This makes the project files bigger and causes ftnchek to do more work later when it reads them to check your complete program. Ordinarily, you should use the -library option to control how much information to store for later use by ftnchek in checking your program.

Here is an example of how to use the UNIX make utility to automatically create a new project file each time the corresponding source file is altered, and to check the set of files for consistency. Add these lines to your makefile. The example assumes that a macro OBJS has been defined which lists all the names of object files to be linked together to form the complete executable program. (In this makefile, the indented lines should each begin with a tab, not blanks.) If any source file contains multiple routines that share common blocks among themselves, then the no-com-\* option should be removed from NOGLOBAL, and/or drop the -library flag.

    # tell make what a project file suffix is
    .SUFFIXES: .prj

    # these options suppress global checks.

    # tell make how to create a .prj file from a .f file
            ftnchek -project $(NOGLOBAL) -library $<

    # set up macro PRJS containing project filenames
    PRJS= $(OBJS:.o=.prj)

    # "make check" will check everything that has been changed.
    check: $(PRJS)
            ftnchek $(PRJS)

When a program uses many routines defined in a large number of different source files in different directories, it can be cumbersome to specify all the different project files needed to check the program properly. To deal with such cases, ftnchek allows project files to be concatenated into a single large file. This single file can then be given to ftnchek to provide the information for checking the use of any or all of the routines defined in the combined project files. When using such a ``library'' project file, you may want ftnchek's error reports to document precisely the name of the file where the specific function is defined. If the various source files are in several directories, an error report that gives only the file name may be ambiguous, and rather should include the path to the file. The solution is to create each of the individual project files by giving the complete path to the source file. Then this complete path will appear in the error reports. For example, suppose that all of the library subprogram source files are in subdirectories of a directory named /util/lib. Then the individual project files could first be created by a command such as

find /util/lib -name '*.f' -exec ftnchek -project '{}' ';'

(Possibly other options would be provided to ftnchek as discussed above. Also, this step could be handled instead by a revised makefile rule that would provide the complete source file path instead of just the local name when invoking ftnchek.) Next, concatenate all of these project files manually.

find /util/lib -name '*.prj' -exec cat '{}' ';' > ourlib.prj

Then a program source file can be checked by using the command

ftnchek prog.f ... -lib ourlib.prj

and an error message related to any library routine will include the full path to the routine's source file.

At present, there is no archive utility like ar to manage the contents of a concatenated project file like the one in the illustration above. If changes are made to one of the library routines, the only way to update the combined project file is to concatenate all the individual project files once again. Such a utility would be quite easy to write. Someone should do so and contribute it to the ftnchek effort.