simple C++ hash_set example

Question

I am new to C++ and STL. I am stuck with the following simple example of a hash set storing custom data structures:

#include 
#include 

        

Answer 1

So close! The last error in your output reveals your hash_trip routine should be declared const:

size_t operator()(const trip t) const // note the ending 'const'
{
    //...
}

You'll probably need to do the same thing for eq_trip. Also, I would recommend passing the arguments to these functions by constant reference to avoid an unnecessary copy of the data you're passing:

size_t operator()(const trip& t) const // note the '&'
{
    //...
}

Answer 2

You should investigate using the STL's TR1 extension namely

• unordered_map
• unordered_set
• unordered_multimap
• unordered_mutliset

Most modern C++ compilers ship with these extensions, hence there is no need to use a non-standard class such as hash_set etc.

• http://en.wikipedia.org/wiki/Unordered_map_%28C%2B%2B_class%29
• http://publib.boulder.ibm.com/infocenter/comphelp/v9v111/index.jsp?topic=/com.ibm.xlcpp9.aix.doc/standlib/stl_unordered_map.htm
• http://www.cplusplus.com/reference/unordered_set/unordered_set/