C/C++ Programming (2021-12-06 - 2021-12-10, 2022-01-24 - 2022-02-04)¶

2021-12-06 ¶

Reiterating on Exercise: Character Histogram
- while ((c = getchar()) != EOF) { ... }: assignment has a value (DRY: don’t repeat yourself)
- Arrays (and everything else) in C are not range checked ⟶ input needs verification
- How far can I write past the end of an array? ⟶ out-of-bounds-write.cpp
  - From the histogram example: what happens if we receive an iso-8859-1 Umlaut character, say “ö”. That character is sure not within range [0,128).
  - From the smaller-scale canary example.
- Aside: C has no bool datatype (C++ has) ⟶ infinite-loop.cpp
Functions
Exercise: Forward Declaration

Solution: power.c
Character Arrays

Char array (i.e., string) walkthrough: strings-wtf.cpp

Massacre using strcpy …
Exercise: Read Line Into String from stdin
Lifetime of Variables

Global variables: global-vs-local.cpp
Type System
Variable Names
Data Types, Sizes
Type Conversions

Demo code: type-system.cpp

Massacre resulting from mixing signed and unsigned integers …
Pointers and Arrays
- Pointers and Addresses
  - pointer-basics.cpp
  - pointer-brainfuck.cpp
- Exercise: Function That Swaps Two Variables
  - Fix that to actually swap the caller’s variables: swap-nok.cpp

Morning wakeup, talking about what happened, questions
- Reiterate on canary and memory errors in general. Security holes, blah, blah. C is the root of all evil.
- argv; that double pointer thing.
  
  Compose an array like argv manually (argv-manually.cpp)
- Double pointers, generally
  
  double-pointer.cpp
- Pointer arithmetic, killing canaries sitting in a row next to an integer
- The same can happen to a function’s return address
- Useful use of pointers: singly linked list
Resolve Exercise: Function That Swaps Two Variables
- swap-nok.cpp
- Not working
- Working
Continuing with Pointers and Arrays
- Pointers and Arrays
- Commandline
  
  Hack a little argv example
Structures
Functions and Program Structure
Pointer Recap: pointer-recap.cpp

Undefined behavior ist commonplace in C. C++ takes long turns to get undefined behavior out of the way. For example:

Array bounds read/write
- It is perfectly ok to read and write past the boundaries of an array. At least this is ok for the compiler; occasionally the program will exhibit undefined behavior - for example when you write into variables in the neighborhood. See undefined-behavior.c.
- C++ brings data structures like std::vector that can do this better. See undefined-behavior-c++.cpp.
Integer overflow bugs are the norm - happily mix signedness and unsignedness, happily mix various integer widths. See overflow-recap.cpp.
Structures (struct) recap; struct-recap.cpp, again with an array bounds write.
Pointers recap; pointer-recap-recap.cpp.
Functions recap; power-recap.c.

What’s that separate compilation unit thing? How do we use the C preprocessor? Dogmatically introducing include guards!
See an example (in C, largely) here.