[SOLVED] Trouble with binary predicate for STL sort in C++

[m_kylli]

I'm trying to create a program that will sort roman numerals stored in a vector by providing a binary predicate, but the compiler complains that the function gets to few arguments.


bool test(const string& a, const string& b)
{
return roman_to_int(a) < roman_to_int(b);
}



sort (romanlist.begin(), romanlist.end(), test());


Can anyone help me out with this problem?

[iharrold]

(return val) roman_to_int(std::string &) is not part of the STL.

I have no idea what it returns, so I just put return val.

I think you are confusing some python code with C++

[m_kylli]

No, roman_to_int is my own function. That one returns the number that the roman numeral represents and works correctly. It's the customized sorting that doesn't work.

[Tuna-Fish]

Can anyone help me out with this problem?



sort (romanlist.begin(), romanlist.end(), test());


look at that call twice. What do you think happens in it?

if you put () after a function, you call it. here you are first calling test with no arguments, then passing it's value to sort.

Try with:


sort (romanlist.begin(), romanlist.end(), test);

[m_kylli]

Well this is embarrassing. It worked. I didn't even think to try that.