Memory & Pointers
Daily Standup
September 05, 2017
Memory Intro
Started learning about memory today and when happens when a program is run: the computer allocates some memory to run the program and partitions the memory for different functions. The stack and heap are shared within the same space; in a C program the stack is at the bottom with the main function making up the base. On top of that, for each function called within main, its data is stacked (and then inner functions stacked further on top, and so on…) until the function has executed & returned (and then erased from the memory store). The heap is where variables and stored values are held, starting at the top and moving downwards towards the stack. Problems happen when these collide.
You can use the malloc() function to tell the computer to allocate a certain amount of free memory to a given variable. This makes sure you don’t overwrite memory that’s needed for something else. You have to pay attention to how much memory is allocated (including a bit for ending strings \0, etc.). You also have to free() the memory once you don’t need it anymore, or it will cause memory leaks, which is a big problem in programs that aren’t closed frequently (ahem Chrome and its billion tabs!).
Pointers
We also learned what’s beneath the string variables that the course helper files allowed. A string doesn’t actually exist, rather it’s a pointer to an address where the beginning of the string is stored in memory. When you call a string the computer goes to that address in memory and pulls back everything up to the end \0 of the string. So the “string” data type we have been using is actually a char *, that is, an address of a character where the string starts in memory.
Three things to remember about pointers:
- Initially pointers don’t point to anything (not setting this up is a huge source of bugs!!)
- You must dereference a pointer to access its pointee
- Assignment
=between pointers makes them point to the same pointee
Other Stuff
I learned what Stack Overflow means!
Up Next
- Watch the concept shorts to really solidify the topics from this lecture.
- Start & finish the homework assignment THIS WEEK! Keep this train rolling…