Let’s Review Pointers

Pointers cause a lot of heartburn among students.  Hopefully this post will address some or all of the things you may be struggling with in the world of pointers.

For pointers to make sense, particularly the parts of them that are important for this class, you need to remember a few fundamental pieces of information:

  • Each location where data can be stored has an address.
    • Analogy: Every post office box in Hughes Trigg has an individual address.  If each didn’t, then the workers wouldn’t know what mail goes in which box.
    • Note that even pointers have addresses.  So, if I have [Read more…]

Memory Diagrams

The fact that c++ allows programmers to manage memory directly is one of its great strengths. It is also something that can lead to a ton of tough debugging and hair-pulling.  There are quite a few “things” a programmer can use to avoid most of these problems, but it is important to understand what’s going on under the hood of C++ so that you can fully understand why those other libraries are useful.

Memory Diagrams can help you not only learn the ins and outs of memory management, but they can also help in a debugging situation as well.  A memory diagram is a drawing that represents the state of the memory used by a program at a particular point in execution.  Of course, it is an abstraction of the actual memory usage, but contains enough detail to be very useful.

A memory diagram usually contains two major sections: 1) stack memory, and 2) heap memory.  These two are usually split between the left and the right on a piece of paper. Here is a template you can have a look at:  Memory Diagram Template.

Here is a link to a screencast on Vimeo I made a couple semesters ago related to drawing memory diagrams.  We’ll also be going over them in class as we talk about memory management.

Some related help:

  • Eric Roberts’ (Stanford) Heap-Stack DiagramsHandout on Heap-Stack Diagrams from their Lab sections (This is a link to some of the PDFs saved in Evernote) – These diagrams are quite a bit more “low level” than the method I use, but the general idea is the same.  The memory diagrams start at Problem 3.  A pdf of the solutions is included as well.
  • Debugging Software Crashes II – quite detailed, but a good resource for understanding memory.

Prep for Data Structures

Data structures is a challenging course.  I routinely receive requests for information about how to prepare for the course or what material to review.  Generally speaking, the most important thing to do is review and get comfortable with C++ and problem solving using C++.  Some of the topics that are of particular importance are:

  • Developing algorithms using fundamental control structures
  • Problem decomposition (breaking a problem down into steps to solve it)
  • Object oriented programming in C++ (classes, inheritance, and polymorphism in c++)
  • Pointers (what they are, how to use them, etc.) including pointers to pointers and arrays of pointers
  • Relationship between pointers and arrays
  • Memory management is a biggie, so I’ll break it down into finer points
    • Dynamic Memory Allocation and deallocation (new, new[], delete, and delete[])
    • What methods you should explicitly include in a class that contains dynamic memory (copy c’tor, overloaded operator =, destructor)
    • Difference between stack and heap (free store)

I don’t expect you to be an expert in all of the topics above, but I would expect that you’ve heard of all of them.  And, at least for some of them, you’ve got a firm understanding of what they are/mean/are used for.

Here are some links to materials from the last time I taught CSE 1342 that you might find useful:

If you’d like any more info on a particular topic, feel free to drop me an email.

Command Line Args in C++

As you’re already familiar with, when you call some functions, you need to pass arguments to them.  So, what about main?  There are two different function headers for he main method in C++ that we can use:

int main (); //header 1

and

int main(int argc, char* argv[]); //header 2

Now, you should ask yourself, “What’s the difference?”  Remember that when you execute a program (either from the command line or by double-clicking on an icon or something similar), you’re really asking the OS to load the executable and begin execution.  When the OS is starting your program, you can use command line arguments to send arguments into the main method.  Consider this program execution:

./myFunGame input.txt output.txt

[Read more…]

Data Structures Intro

The first few weeks of the semester, we’ll take a deep(er) dive into pointers and dynamic memory management using C++.  To get started, I wanted to provide you some links to useful information.

Regarding our first topic, pointers and memory management, here are some links to some other blog posts I did over the summer that might be helpful: