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2012-03-07T00:25:50.710
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You need to learn about references and pointers in C++. These are accesses to existing objects (think "a link to"). The main difference between the two is that there is that if you give a reference to an object, you guarantee that that object exists at the time you pass. If you give a pointer, there may be nothing behind it, this is referred as a "null" pointer (written <code>NULL</code> or <code>nullptr</code>) in recent versions. Here is the main way to use both: <pre><code>int i = 0; int& refToI = i; // create a reference to i int* ptrToI = &i; // create a pointer to i int& anotherRef; // invalid, references must be initialized; int* anotherPtr; // valid, points to garbage data, better set it to NULL though refToI = 1; // i has been changed *ptrToI = 1; // i has been changed, the "*" operator means "content pointed by" </code></pre> Objects (or functions) accepting a reference or a pointer must clarify the lifetime they expect from the pointed objects. That is, once a reference or pointer is created, the object it points too may be destroyed. That's bad, avoid it. Here are some examples in your case: <pre><code>// Solution 1 take a reference to the objet in the function using it class Job; // tells the compiler that there's a Job class somewhere. class Display { public: void DoWork(Job& job) { // write this in the CPP file, I am using a shortcut for the sake of brevity job.DoSomething(); } }; // usage: Display display; Job job; display.DoWork(job); // Solution 2, carry the reference (or pointer) inside the class using it class Job; // tells the compiler that there's a Job class somewhere. class Display { public: Display(Job& job) // !! job must live at least as long as display : _job(job) { } void DoWork() { // write this in the CPP file, I am using a shortcut for the sake of brevity _job.DoSomething(); } private: Job& _job; }; // Usage: Job job; Display display(job); // job and display have the same lifetime, OK display.DoSomething(); </code></pre> <h2>NOTE</h2> There's a debate on whether you should use pointers or references. I think this is a bit harder for you right now. A rule of thumb is use references when lifetimes are well known, use smart pointers when they're not or when using <code>new</code>.
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