Problem with function pointer in class method

[gws923]

Sorry, I posted this in the Beginners forum, but I think it may not be such a beginner topic(?). Please advise if Beginners forum is the right place for this.

Hi there. I'm trying to sort a vector with a custom sort method. I cannot seem to figure out the correct syntax to use std::sort() with the third parameter, since I am trying to do this within class methods, and not my main.cpp file.

Edit: here's the error I'm getting:
error: must use '.*' or '->*' to call pointer-to-member function

Here's what I have:

#include "SpreadSheet.h"

bool SpreadSheet::sortMethod(Sortable* a, Sortable* b)
{
    return a->value() > b->value();
}

void SpreadSheet::sortLinesBy(std::string categoryName)
{
    //m_categories[categoryName] returns an std::vector<Sortable*>
    std::vector<Sortable*> newVector = m_categories[categoryName];
    std::sort(newVector.begin(), newVector.end(), sortSortablesMethod);
}

I have learned through my exploration of the internet that I am dealing with function pointers. I don't quite understand the examples people have posted, but all of them seem to be a bit different than mine anyway.

Does anyone know how I can fix this?

[SakurasouBusters]

Either Beginner or General C++ Programming is fine. This question is not about Windows programming.

[gws923]

Whoops! My mistake. Thank you. I guess this topic should be locked.