Warning on Sun

Question

I was having trouble since long time removing some of the warnings
from my file which was builted on Solaris 9 using C++ compiler 5.0.3.
Your help would be highly appreciated.
Warning message is :
Warning (Anachronism): Formal argument destroy_value_func of type
extern "C" void(*)(Void *) in call to g_hash_table(extern "C" unsigned
(*)(const void*),extern "C" int(*)(const void*,const void*),extern "C"
void (*)(void*),extern "C" void (*)(void*)) is being passed
void(*)(void*).
This kind of several warnings I am getting.
Thanks,

Answer 1

There is no C++ 5.0.3 compiler version. Run the command
CC -V
to find out the compiler version. But the compiler version does not matter for this question.
The "Anachronism" warnings are explained in the C++ MIgration Guide that comes with the compiler. This particular warning is explained in section 3.11, "Pointers to extern C Functions". To find the Migration Guide, point your browser to <install-dir>/docs/index.html and follow the links. By default, <install-dir> is /opt, but your compiler might be installed somewhere else. You can also find the Migration Guide on http://docs.sun.com
Brief answer:
In standard C++, the function linkage is part of the type of a function and of a pointer to function. A pointer to a C-linkage function is not compatible with a pointer to a C++-linkage function, even if the signatures are the same.
On many C++ implementations, the calling sequence of C and C++ linkage functions is the same, so the code will actually work. But the warning is there to tell you that the code is not portable. The Migration Guide explains several ways you can fix your code to make it valid and portable.