For below code:
struct MyStruct
{
char* firstName;
char* secondName;
int age;
};
typedef composite_key
<MyStruct*,
BOOST_MULTI_INDEX_MEMBER(MyStruct, char*, firstName),
BOOST_MULTI_INDEX_MEMBER(MyStruct, char*, secondName)
> comp_key;
typedef multi_index_container
<
MyStruct*,
indexed_by
<
ordered_unique
<
comp_key,
CompareLess
>
>
> MyContainer;
I can easily write a compareless, like below:
struct CompareLess
{ // functor for operator<
static inline int compare(const char* left, const char* right)
{
return strcmp(left, right);
}
inline bool operator()(const char* left, const char* right) const
{ // apply operator<= to operands
return compare(left, right)<0;
}
static inline int compare(const boost::tuple<char*>& x, const char*y)
{
return compare(x.get<0>(),y);
}
inline bool operator()(const boost::tuple<char*>& x, const char*y) const
{
return compare(x,y)<0;
}
static inline int compare(const boost::multi_index::composite_key_result<comp_key>& k, const boost::tuple<char*>& y)
{
return -compare(y,(const char*)(k.value->firstName));
}
inline bool operator()(const boost::multi_index::composite_key_result<comp_key>& k, const boost::tuple<char*>& y) const
{
return compare(k,y)<0;
}
static inline int compare(const boost::tuple<char*>& y, const boost::multi_index::composite_key_result<comp_key>& k)
{
return compare(y,(const char*)(k.value->firstName));
}
inline bool operator()(const boost::tuple<char*>& y, const boost::multi_index::composite_key_result<comp_key>& k) const
{
return compare(y,k) <0;
}
}
But when I want to write something like below:
typedef composite_key
<double,
char*,
char*
> comp_key;
I have trouble writing the compareLess with the below function
static inline int compare(const boost::tuple<char*>& y, const boost::multi_index::composite_key_result<comp_key>& k)
{
return compare(y,(const char*)(k.value->firstName));
}
I don't know how to write some code as "k.value->firstName" to get the char* for comparsion, since the value is no longer a struct, it is only a double. So where can I get the field for comparison? is there something like k.get<0>()?