Custom types as key for a map - C++
- by Appu
I am trying to assign a custom type as a key for std::map. Here is the type which I am using as key.
struct Foo
{
Foo(std::string s) : foo_value(s){}
bool operator<(const Foo& foo1) { return foo_value < foo1.foo_value; }
bool operator>(const Foo& foo1) { return foo_value > foo1.foo_value; }
std::string foo_value;
};
When used with std::map, I am getting the following error.
error C2678: binary '<' : no operator found which takes a left-hand operand of type 'const Foo' (or there is no acceptable conversion) c:\program files\microsoft visual studio 8\vc\include\functional 143
If I change the struct like the below, everything worked.
struct Foo
{
Foo(std::string s) : foo_value(s) {}
friend bool operator<(const Foo& foo,const Foo& foo1) { return foo.foo_value < foo1.foo_value; }
friend bool operator>(const Foo& foo,const Foo& foo1) { return foo.foo_value > foo1.foo_value; }
std::string foo_value;
};
Nothing changed except making the operator overloads as friend. I am wondering why my first code is not working?
Any thoughts?
