how does the structure dereference operator work?

Question

I am a Java programmer trying to teach myself C++.

I would like to understand how the structure dereference operator works. Specifically, what does the following line of code do in explicit terms?

    if (elements[i]->test(arga, argb)) {}

test(arga,argb) is a Boolean function in the same class, and elements is a vector of instances of the element class. Here is the code that immediately surrounds the line above, about which I am interested:

for (unsigned i = 0; i < elements.size(); ++i) {
    T arga = INFINITY, argb = INFINITY;
    //using namespace std;
    //std::cout >> elements[i] >> std::endl;
    //std::cout >> test(arga, argb) >> std::endl;
    if (elements[i]->test(arga, argb)) {
        //some code
    }
}

It seems that the if line is testing to see whether or not the boolean returned by test(arga,argb) is part of the given instance of the elements class. But when I try to expose the underlying values of elements[i] or test(arga,argb) with the cout lines above, the compiler throws errors until I comment those lines out.

In Java, I would be able to fiddle around with this until I found values of each that correspond with each other, and then I would understand the line of code. How can I figure out what this line of code does in C++? I would be interested to see some references online if they are available.

Answer 1

Since numerous respondents told me that I need to provide the code before they can answer, I looked deeper in the code, and re-wrote something which tells me that the line:

if (elements[i]->test(arga, argb)) {}  

is a test to see whether or not the boolean member function of elements[i] is true.

The c++ program that I wrote to identify the meaning of -> in this context is:

#include "stdafx.h"
#include <vector>
#include <string>
#include <iostream>

template<typename T>
class Bone
{
public:
    std::string myName;
    int mySize;
    Bone(const std::string &name, const int &size) : myName(name), mySize(size)
    {}
    bool isBigger(const int &testSize) const
    {
        if (testSize > mySize) return false;
        else return true;
    }
};

int main(int argc, char **argv)
{
    std::vector<Bone<float> *> bones;
    // name, location, size
    bones.push_back(new Bone<float>("femur", 10));
    bones.push_back(new Bone<float>("ulna", 4));
    bones.push_back(new Bone<float>("maxilla", 3));

    int testSize = 6;
    // test each bone to see if it is bigger than testSize
    for (unsigned i = 0; i < bones.size(); ++i) {
        if (bones[i]->isBigger(testSize)) {
            std::cout << bones[i]->myName; std::cout << " is bigger than testSize! " << std::endl;
        }
    }

    while (!bones.empty()) {
        Bone<float> *thisBone = bones.back();
        bones.pop_back();
        delete thisBone;
    }
    return 0;
}

Thank you to everyone who led me to figure this out.