Weekend projects: getting silly with C

It certainly could do though. In C, using an uninitialised variable does not mean "whatever that memory happened to have in it before" (although that is a potential result). Instead, it's undefined behaviour, so the compiler can do what it likes.

For example, it could well unconditionally initialise that memory to 123. Alternatively, it could notice that the whole snippet has undefined behaviour so simply replace it with no instructions, so it doesn't print anything at all. It could even optimise away the return that presumably follows that code in a function, so it ends up crashing or doing something random. It could even optimise away the instructions before that snippet, if it can prove that they would only be executed if followed by undefined behaviour – essentially the undefined behaviour can travel back in time!

  switch(k) {
    if (0) case 0: x = 1;
    if (0) case 1: x = 2;
    if (0) default: x = 3;
  }

  #define brkcase if (0) case

    case 1 ... 10:

    #include <stdio.h> // compile & run: gcc -Wall countdown.c -o countdown && ./countdown
    int n = 10; int main(int argc, char *argv[]) { printf("%d\n", n) && --n && main(n, NULL); }

    import sys # run: python3 countdown.py 10
    def main(n:int): sys.stdout.write(f"{n}\n") and n-1 and main(n-1)
    main(int(sys.argv[1]))

    # run ./countdown.sh 10
    echo $1 && (($1-1)) && $0 $(($1-1))

  4[arr] // same as arr[4]

https://stackoverflow.com/questions/34559705/ternary-conditi...

  #include <stdio.h>
  #include <stddef.h>

  int main()
  {
      {
          int *p = NULL;
          if (p)
          {
          what:
              printf("a = %d\n", *p);
              return 0;
          }
          int a = 123;
          p = &a;
          goto what;
      }
  }

I've seen this in the wild, particularly with macros.

    #define assert(c) if (!c) ...
    
    if (foo) assert(...);
    else bar(); // oops!

Let's stop getting silly with C, too many CVEs!

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Serious comment:

It's a rather cool article actually. Not something I'd do daily but it's kind of sort of useful to know these techniques.

Metaprogramming custom control structures in C by Simon Tatham

I will never love anything as much as I love C, but C development jobs lie in really weird fields I’m not interested in, and I’m fairly certain I am not talented enough. I have seen C wizardry up close that I know I simply cannot do. However, one of the more useful exercises I ever did was implement basic things like a file system, command line utilities like ls/mkdir etc. Sometimes they are surprisingly complex, sometimes no.

After you program in C for a while certain conventions meant to be extra careful kind of bubble up in languages in a way that seems weird to other people. for example I knew a guy that’d auto reject C PR’s if they didn’t use the syntax if (1==x) rather than if (x==1). The former will not compile if you accidentally use variable assignment instead of equality operator (which everyone has done at some point).

This tendency bites me a lot in some programming cultures, people (ime) tend to find this style of programming as overly defensive.