[CoinUtils-tickets] [COIN-OR Common Utilities] #6: Sun CC compiler generates warnings about linkage

[COIN-OR Common Utilities]

#6: Sun CC compiler generates warnings about linkage
------------------------+---------------------------------------------------
 Reporter:  mjs         |       Owner:  somebody
     Type:  defect      |      Status:  new     
 Priority:  minor       |   Milestone:          
Component:  component1  |     Version:          
 Keywords:              |  
------------------------+---------------------------------------------------
 During a make of CLP using the Solaris CC compiler (CC: Sun C++ 5.7
 2005/01/07), the following warnings are generated:
 {{{
 /bin/bash ../libtool --tag=CXX --mode=compile CC -DHAVE_CONFIG_H  -I.
 -I`echo .` -I../inc      -O4  -DNDEBUG -c -o CoinModelUseful2.lo
 CoinModelUseful2.cpp
  CC -DHAVE_CONFIG_H -I. -I. -I../inc -O4 -DNDEBUG -c CoinModelUseful2.cpp
 -KPIC -DPIC -o .libs/CoinModelUseful2.o
 "CoinModelUseful2.cpp", line 764: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 765: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 766: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 767: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 768: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 769: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 770: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 "CoinModelUseful2.cpp", line 771: Warning (Anachronism): Using extern "C"
 double(*)(double) to initialize double(*const)(double).
 8 Warning(s) detected.
 }}}

 The offending lines in CoinModelUseful2.cpp are:
 {{{
      struct init
      {
        char const *fname;
        double (*fnct) (double);
      };

      struct init const arith_fncts[] =
      {
        {"sin",  sin},
        {"cos",  cos},
        {"atan", atan},
        {"ln",   log},
        {"exp",  exp},
        {"sqrt", sqrt},
        {"fabs", fabs},
        {"abs", fabs},
        {NULL, 0}
      };
 }}}
 See the discussion here: http://docs.sun.com/source/819-3689/Ch3.Std.html,
 Section 3.11.
 The problem is that the standard C library functions are declared with "C"
 linkage in the Sun libraries.  The "anachronism" and the fact that they
 are warnings stem from the fact that "C" and "C++" linkage are binary-
 compatible in the Sun libs, but (a) they need not be (in which case,
 things are likely to break), and (b) the C++ standard permits standard C
 lib functions to have either "C" or "C++" linkage.

 The warning can be eliminated in this case by enclosing the declaration of
 struct init in
 extern "C" {...} (and similarly enclosing the declaration of struct symrec
 in !CoinModelUseful.hpp), but for systems where the standard C functions
 have C++ linkage, that won't work.  I can't think of a completely portable
 way to handle this other than to define in !BuildTools a preprocessor
 symbol such as STD_C_FUNCTION_LINKAGE, which is defined to be C or C++
 depending on the compiler and define the structs inside extern
 "STD_C_FUNCTION_LINKAGE" {...}.  Even that's not quite ideal, as the
 structs could then only be used to hold pointers to standard C functions.

-- 
Ticket URL: <https://projects.coin-or.org/CoinUtils/ticket/6>
COIN-OR Common Utilities <http://example.com/>
My example project