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typedef XS(foo) - fails in C++ /w 5.10.0

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From:
Patrick Rutkowski
Date:
January 7, 2008 12:51
Subject:
typedef XS(foo) - fails in C++ /w 5.10.0
Message ID:
000901c8516f$1aa1cc10$6a03640a@gridapp.com
Outlined below is a problem I ran into today followed by a suggested fix.

First, some background information. XSUB.h in 5.8.8. defined the macro
XS(name) as such:

===== START CODE =====

    #if defined(__CYGWIN__) && defined(USE_DYNAMIC_LOADING)
    #  define XS(name) __declspec(dllexport) void name(pTHX_ CV* cv)
    #else
    #  ifdef HASATTRIBUTE_UNUSED
    #    define XS(name) void name(pTHX_ CV* cv __attribute__unused__)
    #  else
    #    define XS(name) void name(pTHX_ CV* cv)
    #  endif
    #endif

===== END CODE =====


The main version of the definition I’m interested is “#define XS(name) void
name(pTHX_ CV* cv)”.
 
In 5.10.0 these definitions changed to the following:

===== START CODE =====

    /* XSPROTO() is also used by SWIG like this:
     *
     *     typedef XSPROTO(SwigPerlWrapper);
     *     typedef SwigPerlWrapper *SwigPerlWrapperPtr;
     *
     * This code needs to be compilable under both C and C++.
     *
     * Don't forget to change the __attribute__unused__ version of XS()
     * below too if you change XSPROTO() here.
     */
    #define XSPROTO(name) void name(pTHX_ CV* cv)
    
    #undef XS
    #if defined(__CYGWIN__) && defined(USE_DYNAMIC_LOADING)
    #  define XS(name) __declspec(dllexport) XSPROTO(name)
    #endif
    #if defined(__SYMBIAN32__)
    #  define XS(name) EXPORT_C XSPROTO(name)
    #endif
    #ifndef XS
    #  if defined(HASATTRIBUTE_UNUSED) && !defined(__cplusplus)
    #    define XS(name) void name(pTHX_ CV* cv __attribute__unused__)
    #  else
    #    ifdef __cplusplus
    #      define XS(name) extern "C" XSPROTO(name)
    #    else
    #      define XS(name) XSPROTO(name)
    #    endif
    #  endif
    #endif

===== END CODE =====


The main definition I’m interested here is the __cplusplus specific one:
“#define XS(name) extern "C" XSPROTO(name)”.


== THE PROBLEM ==

I have some code (namely XML::Xerces-2.7.0-0’s Xerces.cpp source file) which
does one of these:

    *code*: typedef XS(SwigPerlWrapper);

Now, on 5.8.8 this would evaluate to something the following statement,
which is all well and good:

    *code*: typedef void SwigPerlWrapper(pTHX_ CV* cv);

However, on 5.10.0 it evaluates to:

    *code*: typedef extern “C” void SwigPerlWrapper(pTHX_ CV* cv);

The “extern “C”” part makes the compiler die with the following message:

error: expected unqualified-id before string constant
error: expected `,' or `;' before string constant


== PROPOSED FIX ==

I propose that there be a new macro added called XS_TYPEDEF. This macro
would be defined in the usual way when __cplusplus is not present:

#define XS_TYPEDEF(name) typedef XS(name)

However, when __cplusplus is defined it would be set to something like this:

#define XS_TYPEDEF(name) extern “C” { typedef XS(name); }

What do you guys think?

-Patrick



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