Memory Management - robbiehume/CS-Notes GitHub Wiki

• When you run functions and when things go in and out of scope (curly brackets), the compiler allocates space on the stack for the variables inside that scope
• When a function returns, those variables get popped off the stack and the stack pointer is adjusted
• When something is declared as a pointer (with new?), it's on the heap
• For every malloc()/new, you must have a free()/delete
• Every time you delete a pointer, it should be set to NULL
• -> pointer dereference is preferred for method calls on object pointers

• When using pointers, always use memory from the heap

• Notes on pointers from C/C++ wiki

• Memory leak: memory that hasn't been freed and there is no way to access (or free) it
  • Will occur if pointers aren't deleted (freed) before it goes out of scope
  • If the program runs long enough it could run out of memory or other potential issues
• Dangling pointer: points to memory that has already been freed
  • Trying to access it may cause a segmentation fault
• Segmentation Fault: error caused by trying to access memory that doesn't exist or that the program is not allowed to access. It will crash the program
• Stack overflow: occurs when a program tries to use more memory space in the call stack than has been allocated to that stack
  • Common causes: infinite or excessively deep recursion, very large local variables, excessive function call nesting

Stack:

• Allocated per application; set amount per app
• Managed by the compiler
• Stores local variables

Heap:

• Limited by system memory
• Uses pointers; must dynamically manage it (test with valgrind)
• Benefit of storing things in the heap is you only need to use as much memory as you need to
• Allows for memory to be shared across separate threads and even between processes