C13 Compiling files in Cactus seems to involve three steps, preprocessing,

    compiling, and then postprocessing. What are they doing?

    Cactus specific preprocessing is performed for most source files, for
    example to expand c-preprocessor macros (e.g. DECLARE_CCTK_PARAMETERS)
    in .F, .F90 and .F77 files or to set correct names for calling Fortran
    functions in C files.  At the end of the preprocessing stage the
    resulting source file is placed into the

       configs/<config>/build/<thorn>

    directory and if ready to be passed to the compiler.

    Once a file has been preprocessed, the resulting source file is
    compiled, with the working directory set to

      configs/<config>/scratch

    (which ensures, for example, that all F90 modules can be found by
    the compiler).

    After the file is compiled, some architectures may require
    postprocessing of the object files, for example,some machines
    don't allow the use of a "-o" flag for naming the resulting
    object file, in which case part of postprocessing would involve
    renaming and moving the file.


C32 What is the Cactus c-preprocessor (Cactus cpp) ?

    Part of the pre-processing step for Fortran files involves the use of
    the C-preprocessor.  On some architectures the native CPP does not
    correctly handle spaces in source files, and thus corrupts the
    resulting file.  On other machines there is no native way to generate
    dependency information for files.  In an attempt to solve these problems
    we have written a replacement of CPP in perl, which you may use if you
    configure with

      CPP='$${PERL} $${CCTK_HOME}/lib/sbin/cpp.pl'

    or in an options file without the quotes

      CPP=$${PERL} $${CCTK_HOME}/lib/sbin/cpp.pl

    The Cactus preprocessor is still being developed and improved, known
    problems include

      - only currently supports #ifdef, #if defined for a single token and
        not operations involving more than one token connected by && and ||,
        etc
      - problems with macros whose overall expansion contains the original
        macro name

    The Cactus make system does not use the standalone CPP to preprocess C
    source files, as the first step of a C compilation involves the use of
    a CPP (normally internal).  In any case we do not recommend the use of
    this perl CPP to process C files, partly due to the above problems, and
    partly as the preprocessor does not pre-define certain symbols which
    the native preprocessor would..


git-svn-id: http://svn.cactuscode.org/flesh/trunk@3179 17b73243-c579-4c4c-a9d2-2d5706c11dac

1 files changed, 59 insertions, 6 deletions

diff --git a/doc/FAQ b/doc/FAQ
index 42dfa119..1605d676 100644
--- a/doc/FAQ
+++ b/doc/FAQ
@@ -1,7 +1,7 @@
 
 Cactus Code Frequently Asked Questions
 
-$Header: /mnt/data2/cvs2svn/cvs-repositories/Cactus/doc/FAQ,v 1.62 2003-03-17 15:13:07 allen Exp $
+$Header: /mnt/data2/cvs2svn/cvs-repositories/Cactus/doc/FAQ,v 1.63 2003-03-19 12:30:26 allen Exp $
 
 Also available at http://www.cactuscode.org/Documentation/FAQ
 
@@ -81,7 +81,7 @@ C12 I get the following error when compiling?
     gmake: *** [wave] Error 2
 
 C13 Compiling files in Cactus seems to involve three steps, preprocessing,
-    compiling, and then postprocessing. What is the postprocessing step for?
+    compiling, and then postprocessing. What are they doing?
 
 C14 When trying to create the Cactus executable I get the error the
     error <Unresolved text symbol "SetCartSymVN" -- 1st referenced
@@ -142,6 +142,38 @@ C31 Why can't I use different F90 and F77 compilers with Cactus?
 C31 I just want to check that one thorn compiles correctly, can I test 
     this without compiling all the thorns which come before it?
 
+C32 What is the Cactus c-preprocessor (Cactus cpp) ? 
+
+    Part of the pre-processing step for Fortran files involves the use of
+    the C-preprocessor.  On some architectures the native CPP does not
+    correctly handle spaces in source files, and thus corrupts the
+    resulting file.  On other machines there is no native way to generate
+    dependency information for files.  In an attempt to solve these problems
+    we have written a replacement of CPP in perl, which you may use if you
+    configure with
+
+      CPP='$${PERL} $${CCTK_HOME}/lib/sbin/cpp.pl'
+
+    or in an options file without the quotes
+
+      CPP=$${PERL} $${CCTK_HOME}/lib/sbin/cpp.pl
+
+    The Cactus preprocessor is still being developed and improved, known 
+    problems include
+
+      - only currently supports #ifdef, #if defined for a single token and
+        not operations involving more than one token connected by && and ||, 
+        etc
+      - problems with macros whose overall expansion contains the original 
+        macro name
+
+    The Cactus make system does not use the standalone CPP to preprocess C
+    source files, as the first step of a C compilation involves the use of
+    a CPP (normally internal).  In any case we do not recommend the use of
+    this perl CPP to process C files, partly due to the above problems, and
+    partly as the preprocessor does not pre-define certain symbols which
+    the native preprocessor would..
+
 
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 Running:
@@ -579,14 +611,33 @@ C12 I get the following error when compiling?
 
 
 C13 Compiling files in Cactus seems to involve three steps, preprocessing,
-    compiling, and then postprocessing. What is the postprocessing step
-    for?
+    compiling, and then postprocessing. What are they doing?
 
-    This is for architecture dependent things which come up. For example,
-    some machines don't allow using a "-o" flag for naming the resulting
+    Cactus specific preprocessing is performed for most source files, for 
+    example to expand c-preprocessor macros (e.g. DECLARE_CCTK_PARAMETERS) 
+    in .F, .F90 and .F77 files or to set correct names for calling Fortran 
+    functions in C files.  At the end of the preprocessing stage the
+    resulting source file is placed into the
+
+       configs/<config>/build/<thorn>
+
+    directory and if ready to be passed to the compiler.
+
+    Once a file has been preprocessed, the resulting source file is
+    compiled, with the working directory set to
+
+      configs/<config>/scratch
+
+    (which ensures, for example, that all F90 modules can be found by
+    the compiler).
+
+    After the file is compiled, some architectures may require
+    postprocessing of the object files, for example,some machines
+    don't allow the use of a "-o" flag for naming the resulting
     object file, in which case part of postprocessing would involve
     renaming and moving the file.
 
+
 C14 When trying to create the Cactus executable I get the error
 
     Creating cactus_origin in /data2/convCactus/exe from
@@ -885,6 +936,8 @@ C31 I just want to check that one thorn compiles correctly, can I test
     builds thorns in the order they appear in the list. (Note, this does 
     not link any thorn libraries together).
 
+C32 What is the Cactus c-preprocessor (Cactus cpp) ? 
+
 
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