On Dec 5, 5:50 am, t.lehm...@rtsgroup.net wrote:
In the example I'm trying to store a (instance, method) pair
as key in a map, but I'm failing because of a comparison "<"
in the "std::pair"! (code after dashed line in example)
You might try:
template<typename X> struct MethodComparator {
union Transfer {
SIMPLE_METHOD m;
char bytes[sizeof(SIMPLE_METHOD)];
}; // Used because reinterpret_cast<char*>(memfun_ptr) is illegal.
bool operator()(const KEY_METHOD& lhs, const KEY_METHOD& rhs) {
if (lhs.first < rhs.first) return true;
if (rhs.first < lhs.first) return false;
// Important lines:
Transfer lhs_method;
lhs_method.m = lhs.second;
Transfer rhs_method;
rhs_method.m = rhs.second;
return lexicographical_compare(lhs_method.bytes, lhs_method.bytes
+ sizeof(lhs_method.bytes),
rhs_method.bytes, rhs_method.bytes
+ sizeof(rhs_method.bytes));
}
};
typedef std::map<KEY_METHOD, WrapperBase*, MethodComparator>
METHOD_MAP;
Here I'm comparing the bit patterns of the two method pointers. This is
undefined according to the standard, but I suspect that many or most
compilers do the Right Thing.
This is not so. There could well be padding bytes in the
Transfer-class. All in all, it is difficult to device a nice way out of
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