[Swig-devel] [ swig-Bugs-1844386 ] amd64: .cpp generate file don't compile

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Bugs item #1844386, was opened at 2007-12-04 21:02
Message generated for change (Comment added) made by olly
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Category: code generation (general)
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Loux (loux_thefuture)
Assigned to: Nobody/Anonymous (nobody)
Summary: amd64: .cpp generate file don't compile

Initial Comment:
i use swig from a while now and every thing is fine,
except that i compile now on nocona and the same files don't compile now :(
here is a sample (i cut everything else from .cpp generate from .i: 
#include <stdio.h>
void function() {
  void *argp4 ;
  va_list arg4 ;
  if (!argp4) {
     SWIG_exception_fail(SWIG_ValueError, "invalid null reference " "in method '" "new_psSystemMessage" "', argument " "4"" of type '" "va_list""'");
    } else {
      va_list * temp = reinterpret_cast< va_list * >(argp4);
      arg4 = *temp;
      if (SWIG_IsNewObj(res4)) delete temp;
      }
}
int main(int argc, char *argv[])
{
  function();
  return 0;
}
on a x86 this code compile well (gcc-4.1.2)
but on a amd64 this code don't compile :(
i got ISO C++ interdit l'affectation de tableaux
could someone look at that please ?
i'll be glade to give more details if need


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>Comment By: Olly Betts (olly)
Date: 2008-01-17 03:30

Message:
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We don't have a va_list to copy here though, so va_copy is no help.  We're
converting parameters from the scripting language (Python in your case) to
C++, so what we need to do is convert the trailing Python parameters to a
va_list.  But we can't build a va_list directly - all we can do is to
specify what the "..." can be (as the manual describes), and essentially
generate wrappers for this set of overloaded functions.

The current generated code you are getting is just wrong - it's SWIG's
generic parameter conversion, applied to va_list.  Even if that compiles,
it isn't going to work (at least not in a useful way).

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Comment By: Felipe Sateler Perez (fsateler)
Date: 2008-01-17 02:11

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Note that C99 specifies a va_copy macro that fits exactly this purpose.
Don't know what the status of C99 acceptance in compilers, though (or in
C++ compilers, for that matter).

----------------------------------------------------------------------

Comment By: Olly Betts (olly)
Date: 2008-01-17 01:19

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I don't think this is specific to Python, so marking as "general code
gen".

Wrapping a function taking va_list isn't currently possible with SWIG -
see:

http://www.swig.org/Doc1.3/Varargs.html#Varargs_nn8

I think the text there is a bit pessimistic though - I think we should be
able to automatically generate a C/C++ function with varargs (i.e. ... in
the prototype) in place of the va_list which just sets up a va_list and
then calls the va_list function.  Then we can wrap the automatically
generated function instead.  But we don't currently do that (and I don't
have plans to work on it myself in the foreseeable future).

For now at least, you should be able to use %extend to write such a
wrapper for yourself (and wrap it as the manual explains), and then use
%ignore to ignore the va_list version.

Or if the API being wrapped already has a "..." equivalent, just %ignore
the va_list variant.


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Comment By: Felipe Sateler Perez (fsateler)
Date: 2008-01-16 12:59

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I have created a small testcase (copied below, how does one attach things
here?). 
This is the result on amd64:

% swig -c++ -classic -python a.i
% g++ -c -fPIC a.cpp a_wrap.cxx -I/usr/include/python2.4
a_wrap.cxx: In function ‘PyObject* _wrap_vararg_vfunction(PyObject*,
PyObject*)’:
a_wrap.cxx:2789: error: invalid array assignment

--- a.cpp
#include <stdio.h>
#include <stdarg.h>

void vararg_vfunction( int n_args, va_list list) {
        int i;

        for( i = 0; i < n_args; i++ ) {
                printf("%d ", va_arg(list, int) );
        }
}

void vararg_function(int n_args, ...) {
        va_list list;
        va_start(list,n_args);
        vararg_vfunction( n_args, list );
        va_end(list);
}

--- a.i
%module a
%{

void vararg_function(int n_args, ...);
void vararg_vfunction(int n_args, va_list list);

%}

void vararg_function(int n_args, ...);
void vararg_vfunction(int n_args, va_list list);

----------------------------------------------------------------------

Comment By: William Fulton (wsfulton)
Date: 2007-12-09 12:53

Message:
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Please supply a small standalone interface file showing the problem.
Supplying the generated code without the source makes hunting for the bug a
guessing game.

----------------------------------------------------------------------

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