# CXREF VERSION 1.6 - FREQUENTLY ASKED QUESTIONS AND ANSWERS

This file contains a list of frequently asked questions and their answers relating to cxref version 1.6. Not all of the questions here are real users questions, some of them have been made up to give some help to people trying to use the program who find that the README documentation is insufficient.

Section 0 - Why doesn't this FAQ answer my question?

Section 1 - What does cxref do (and what it doesn't)

Q 1.1 Does cxref support C++?

Q 1.2 Does cxref show which #includes that are not needed?

Q 1.3 Can cxref document automatic function variables?

Q 1.4 Does cxref run on systems other than UNIX?

Section 2 - When cxref does not work

Q 2.1a How do I find out what is causing the parse error?

Q 2.1b What does this parse error message mean?

Q 2.2 Where is the file cxref.html referenced from README.html?

Q 2.3 Why are half of the cross references missing?

Q 2.4 Why can't cxref process my header file in isolation?

Q 2.5 Why can't LaTeX process the output files?

Q 2.6 Why does the include file name have the complete path name?

Q 2.7 Why does the include file name have the wrong path name?

Q 2.8 Why does cxref put in links to system include files?

Section 3 - How to make cxref do what you want

Q 3.1 How do I use cxref to process source files in more than one directory?

Q 3.2 How can I add my own information to the output files?

Q 3.3 Can I get a subset of the cross-reference information?

Q 3.4 Is there an easy way to generate the comments in the correct format?

Q 3.5 How do I produce LaTeX output from a single source.c.tex output file?

Q 3.6 How can I pass extra arguments to the C pre-processor?

Q 3.7 Can I cross-reference my source code at the same time as compiling it?

Q 3.8 What use is the .cxref configuration file?

Section 4 - More information about cxref

Q 4.1 Who wrote cxref, When and Why?

Q 4.2 How do I find out more information about cxref?

## Section 0 - Why doesn't this FAQ answer my question?

This FAQ is released with each new version of the cxref program, so if the question is one that is frequently asked about the new version then you will by definition not find the answer here. You can find the latest information about cxref at the cxref web-page, this contains among other things a list of bug-fixes for the latest version. http://www.gedanken.org.uk/software/cxref/

## Section 1 - What does cxref do (and what it doesn't)

### Q 1.1 Does cxref support C++?

    No.

    The cxref program only works for C, More specifically:

    1) ANSI standard C with some leniency for common non-ANSI syntax.
            For example, the construct 'switch(foo) { case 1: ... default: }' is not
            ANSI, there must be a ';' after the default label, but it is accepted by
            cxref.

    2) Traditional (K&R) function declarations, with implicit 'int' and 'void'.
            For example 'foo(){}' is parsed as if 'int foo(void){}' was specified.

    3) The ability to parse GCC extensions.
            The GCC '__attribute__' and '__extension__' keywords and most of the
            other GCC extensions. The 'inline' keyword is allowed.

### Q 1.2 Does cxref show which #includes that are not needed?

    No.

    The output of the cxref program cross-references all of the functions,
    variables, type definitions, included file etc.  There is not a way of
    identifying files that are included in another source file that do not need to
    be.

### Q 1.3 Can cxref document automatic function variables?

    No.

    The inclusion of automatic variables in the output is not included.  This is
    because of the number of them in a typical function.  In theory it could be made
    to do this.

### Q 1.4 Does cxref run on systems other than UNIX?

    For example DOS / Win3 / Win95 / WinNT / OS/2.

    UNIX    = Yes
            This is the system that the program way designed and initially written
            for, it should work on many versions of UNIX.
            I know that it works on Linux, SunOS 4.1.x, Solaris 2.x, AIX & HP-UX 10.

    DOS/Win3 = No
            The program was not designed for DOS, the filenames used and the
            multi-process nature of the program do not allow this.

    Win95/WinNT = Yes
            Using the Cygwin library and tools http://cygwin.com/ it is possible to
            compile and run the programs.

    OS/2    = Maybe
            I have reports that it is possible with OS/2 Warp with emx, but I do not
            support cxref for this OS.

## Section 2 - When cxref does not work

### Q 2.1a How do I find out what is causing the parse error?

    The following error message is generated by cxref when parsing a source file
    (with YYDEBUG set to 0 in parse-yy.h when cxref was compiled).

    test.c:   4: parse error, expecting `','' or `';''
    ^^^^^^  ^^^  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    file    line            type of error
    name    number        generated by yacc

    The error is on line 4 of the file test.c.  In this case, the error message that
    the yacc parser is generating is of some help, more often the error message is
    just 'parse error'.

    If YYDEBUG was set to 1 in parse-yy.h, then a more detailed error message would
    be given (See Q 2.1b).

### Q 2.1b What does this parse error message mean?

    The following error message is generated by cxref when parsing a source file
    (with YYDEBUG set to 1 in parse-yy.h when cxref was compiled).

    test.c:   4: parse error, expecting `','' or `';''

    The previous 10, current and next 10 symbols are:
     -8 | 296 :              INT : int
     -7 | 258 :       IDENTIFIER : foo
     -6 |  40 :                  : (
     -5 | 292 :             VOID : void
     -4 |  41 :                  : )
     -3 | 123 :                  : {
     -2 | 296 :              INT : int
     -1 | 258 :       IDENTIFIER : a
      0 | 296 :              INT : int
      1 | 258 :       IDENTIFIER : b
      2 |  59 :                  : ;
      3 | 125 :                  : }
    END OF FILE
    ^^^               ^^^^^^^^^^  ^^^^^
    symbol              symbol    symbol
    number               type     value

    From this we can reconstruct part of the file test.c, using the previous and
    next 10 symbol values from the lexer.

    int foo(void) { int a   int b; }
                          ^
    This is where the parse error occurred, after 'int a' and before 'int b;'.
    The cause of the error is now clear, there is a ';' missing after the
    declaration of the variable a.

    The cxref program is intended to be used on source files that are known to
    compile with a C compiler.  In this case a parse error message should not be
    seen except for either non-standard C, (and compiler) or a bug in cxref.

### Q 2.2 Where is the file cxref.html referenced from README.html?

    The README.html file has a reference to the file cxref.html, this file is only
    present when 'make docs' has been run to generate the cross references for the
    cxref program itself.  The file is in the example sub-directory of the doc
    directory.

### Q 2.3 Why are half of the cross references missing?

    The way that cxref works is that it processes all of the source files for a
    program, one at a time and generates a cross reference database.  A second pass
    of the program is required to generate all of the cross references from the
    database of cross reference information.

    For this reason, the Makefile for the doc directory of cxref uses 'cxref *.c
    -xref -Odoc' for the first pass and 'cxref *.c -xref -Odoc -html -latex' for the
    second pass.  The first to build the database, the second to produce the
    outputs.

    The reason that the cross references are missing is that only one pass of the
    program has been done on all of the files.  The later files to be be processed
    will have cross references for the earlier files processed.

### Q 2.4 Why can't cxref process my header file in isolation?

    The cxref program needs to process the header files to enable a cross reference
    for them to be generated.  In many cases, the header file will not have been
    written with this in mind, and may rely on other header files being included
    before the one being processed.  The best solution to this is to modify the
    header file so that it includes all of the header files that it needs.

    Another option is to use '-- -include filename.h' on the command line.  This
    will include the specified file (filename.h) into the source file that is being
    processed at the beginning.

    There is a Perl script supplied with the cxref source files called fixheader.
    This can be used to automatically determine what header files may be required.
    The decision is based on the header files that are used for the files that cxref
    can process and lots of test compilations.

### Q 2.5 Why can't LaTeX process the output files?

    The LaTeX output is designed to work with LaTeX version 2e and the output files
    will not work with the much older LaTeX version 2.0.9.

    The file cxref.tex (or basename.tex if '-Nbasename' is used) is the file that
    must be processed by LaTeX.

### Q 2.6 Why does the include file name have the complete path name?

    This is because a standard C preprocessor is being used instead of cxref-cpp or
    an appropriate version of gcc.  Changes were made in version 2.8.0 of gcc that
    make it output the names of the include files as they are in the original source
    code and not after the files have been translated into an absolute pathname.

### Q 2.7 Why does the include file name have the wrong path name?

    If the answer to this question is not the same as the answer to Q 2.6 then it
    could be the following.  When the files that are being cross-referenced are in a
    directory that contains a symbolic link in the path then the current directory
    has two (or more) possible names.  The way that the cxref program works is that
    it finds the current working directory (which is the real pathname, not using
    any links).  If the name that you specify using -R is another name for the same
    directory then cxref will not realise that they are the same.  This can cause
    the pathnames to become confused.  Try using relative pathnames where possible
    for the -R and -I options.

### Q 2.8 Why does cxref put in links to system include files?

    The way that cxref knows which include files are local to the program and which
    ones are system ones is by the way that they are included.  Any that use double
    quotes '"' are local ones and wil have links to them included in the cross
    reference output.  The include files that use the angle brackets '<>' are system
    files and do not have links to them included.

    The best solution is to change the include files so that the distinction is
    clear.  An alternative is to use the '-isystem DIRNAME' option of gcc.  This
    will cause gcc to treat files in this directory as if they are system files.
    Since cxref uses gcc for the pre-processing, this option can be passed through
    using 'cxref file.c -- -isystem DIRNAME'.

## Section 3 - How to make cxref do what you want

### Q 3.1 How do I use cxref to process source files in more than one directory?

    The cxref program depends on a database of cross references, these must all be
    consistent.  This requires that all of the files to be cross referenced are in
    the same directory tree.

    Example:

    directory     files
    - - - - -     - - -
    basedir    :  f0.c f0.h ...
     |- s1     :  f1.c f1.h ...
     |- s2     :  f2.c f2.h ...
    ...

    -- f2.c --
    #include <...>
    #include "f2.h"
    #include "../s1/f1.h"
    #include "f0.h"
    ----------

    In the base directory 'basedir' run 'cxref -xref -Odoc s2/f2.c -html -I.'.  This
    will create the file 'doc/s2/f2.c.html' for the file 'f2.c' and this will
    contain references to the files 'doc/s2/f2.h.html', 'doc/s1/f1.h.html' and
    'doc/f0.h.html'.  The subdirectories 'doc/s1', 'doc/s2' will be automatically
    created within the 'doc' directory to put the files into (the 'doc' directory
    must already exist).

    directory        files
    - - - - -        - - -
    basedir
     |- doc       :  f0.c.html f0.h.html ... cxref.html
         |- s1    :  f1.c.html f1.h.html ...
         |- s2    :  f2.c.html f2.h.html ...
    ...

    An alternative method is to use the -R option to cxref.  In the directory 's2',
    cxref can be run as 'cxref -R.. -xref -Odoc f2.c -html -I.'.  This will change
    directory to '..' ('basedir') before cxref is run, and will modify the cxref
    arguments so that it is equivalent to running cxref from 'basedir' as detailed
    above.

### Q 3.2 How can I add my own information to the output files?

    The files cxref.html and cxref.tex (depending on whether using HTML or LaTeX
    format and the use of the '-Nbasename' option) are the ones to edit.  These
    files contain the lines 'Begin-Of-Source-Files' and 'End-Of-Source-Files' as
    comments.  The output files for each source file are automatically included
    between these lines if they do not already exist there.  The order of these
    files and any other text between these lines is not important.  Customisation of
    the files should be added here.  The output files for each source file are
    automatically generated so any edits made to these will be lost when cxref is
    run.

### Q 3.3 Can I get a subset of the cross-reference information?

    At the moment, the only one way to limit the amount of cross referencing is to
    use the '-xref-*' command line option (see README).  There are plans for a
    future version of cxref to have an options file that would allow different
    amounts of information to be generated in the output.  For example, only to
    display called and not calls information for each function.

### Q 3.4 Is there an easy way to generate the comments in the correct format?

    The only easy way to do this is to use the cxref.el macro file and Emacs.  This
    is what is used to generate the comments in the cxref source code itself.

### Q 3.5 How do I produce LaTeX output from a single source.c.tex output file?

    The file cxref.tex (or basename.tex if '-Nbasename' is used) is the file that
    must be processed by LaTeX.  All of the individual LaTeX files for the source
    files are included into this file.  If an individual file source.c.tex needs to
    be processed then a copy of the file cxref.tex should be modified to include
    only the required source.c.tex file.

### Q 3.6 How can I pass extra arguments to the C pre-processor?

    The cxref program itself has three ways that you can specify the arguments that
    are passed to the C pre-processor.

    a) The -CPP option allows the name of the pre-processor program itself to be
       changed.
       e.g. 'cxref -CPP "/usr/foo/cpp -C" foo.c' will use the cpp from /usr/foo
       instead of the compiled in default and pass it the option -C.

    b) The most common C pre-processor commands are recognised by cxref
       automatically, these are -D*, -U* and -I*.

    c) Any amount of extra options can be passed to the preprocessor by appending
       them to the command line after the end-of-arguments marker '--'.
       e.g. 'cxref foo.c -- -traditional' will pass -traditional to the
       pre-processor.

### Q 3.7 Can I cross-reference my source code at the same time as compiling it?

    It is possible to cross-reference and document your source code at the same time
    as compiling it by using the cxref-cc script.  This takes the same arguments as
    your usual C compiler and performs both functions.

    First it calls the C compiler and passes on all of the command line arguments.
    The real C compiler is specified by the CXREFCC environment variable, or the CC
    environment variable or it will use gcc if neither of these are set.

    Second the arguments that cxref needs to have are extracted from the arguments
    that the C compiler had and cxref is called.  The arguments that are kept are
    the -D*, -U*, -I* arguments to specify #defines and #include paths, and the file
    name of the source file itself.  Any other arguments are taken from the .cxref
    file (See Q 3.8).

    After doing this it will still be necessary to sort out the header files since
    these are not cross-referenced using this method.

### Q 3.8 What use is the .cxref configuration file?

    The most obvious use is if you have a lot of command line options that you don't
    want to have to enter every time that you run the program.

    However the .cxref file is most useful when you have a multiple directory source
    tree (See< Q 3.1), or when you are using an existing Makefile to build
    documentation.

    When there are various subdirectories containing source code, a .cxref file in
    each sub-directory can be used just containing the line '-R..' or whatever is
    appropriate to point cxref to the root of the source tree.  This means that
    there is no need to keep track of which directory you are in, they all will use
    the correct directory to work from.

    If you already have a Makefile that goes through all of the source code then you
    may want to modify it so that it calls cxref instead of calling the C compiler.
    This means that there is no room to put the extra arguments to cxref on the
    command line.  A .cxref file can contain the command line arguments so that you
    only need to need the arguments that are already there for the C compiler
    (See Q 3.7).

## Section 4 - More information about cxref

### Q 4.1 Who wrote cxref, When and Why?

    The cxref program was written by Andrew M. Bishop in 1995-2004 and maintained
    since then.

    An earlier program by the same author using basically the same comment
    convention was written in Emacs Lisp in 1994.  This version was slow, the amount
    of cross referencing was poor and the output was only in troff format.  The
    current C program was written to replace this but has grown to become much
    better in the cross referencing that is done and the format of the output has
    increased greatly.

    The cxref program can be freely distributed according to the terms of the GNU
    General Public License (see the file `COPYING').

### Q 4.2 How do I find out more information about cxref?

    There is a cxref homepage at http://www.gedanken.org.uk/software/cxref/.  This
    is kept updated with news about the program, as new versions become available.

    The web page also contains contact information for reporting bugs by e-mail.