AMIY K.... cmdneo

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Falsehoods programmers believe about time

This is a compiled list of falsehoods programmers tend to believe about working with time.

Don't re-invent a date time library yourself. If you think you understand everything about time, you're probably doing it wrong.

Falsehoods

There are always 24 hours in a day.
February is always 28 days long.
Any 24-hour period will always begin and end in the same day (or week, or month).

Here's a list of mildly interesting things about the C language that I learned mostly by consuming Clang's ASTs. Although surprises are getting sparser, I might continue to update this document over time.

There are many more mildly interesting features of C++, but the language is literally known for being weird, whereas C is usually considered smaller and simpler, so this is (almost) only about C.

1. Combined type and variable/field declaration, inside a struct scope [https://godbolt.org/g/Rh94Go]

struct foo {
   struct bar {
 int x;

	;;
	;; NS CHEATSHEET
	;;
	;; * :require makes functions available with a namespace prefix
	;; and optionally can refer functions to the current ns.
	;;
	;; * :import refers Java classes to the current namespace.
	;;
	;; * :refer-clojure affects availability of built-in (clojure.core)
	;; functions.

	Latency Comparison Numbers (~2012)
	----------------------------------
	L1 cache reference 0.5 ns
	Branch mispredict 5 ns
	L2 cache reference 7 ns 14x L1 cache
	Mutex lock/unlock 25 ns
	Main memory reference 100 ns 20x L2 cache, 200x L1 cache
	Compress 1K bytes with Zippy 3,000 ns 3 us
	Send 1K bytes over 1 Gbps network 10,000 ns 10 us
	Read 4K randomly from SSD* 150,000 ns 150 us ~1GB/sec SSD

	#include <stdlib.h>
	#include <unistd.h>
	#include <stdio.h>
	#include <fcntl.h>
	#include <linux/fb.h>
	#include <sys/mman.h>
	#include <sys/ioctl.h>
	#include <stdint.h>
	#include <stdbool.h>
	#include <linux/input.h>

	// Just before switching jobs:
	// Add one of these.
	// Preferably into the same commit where you do a large merge.
	//
	// This started as a tweet with a joke of "C++ pro-tip: #define private public",
	// and then it quickly escalated into more and more evil suggestions.
	// I've tried to capture interesting suggestions here.
	//
	// Contributors: @r2d2rigo, @joeldevahl, @msinilo, @_Humus_,
	// @YuriyODonnell, @rygorous, @cmuratori, @mike_acton, @grumpygiant,

	/* gcc -O2 -Werror -I/usr/include/libpng16 -lpng png.c -o png */

	#include <stdio.h>
	#include <stdlib.h>
	#include <png.h>

	typedef struct PNG {
	int width;
	int height;
	int depth;

	import java.io.FileDescriptor;
	import java.io.FileOutputStream;
	import java.io.IOException;
	import java.io.OutputStream;
	import java.io.PrintStream;

	public class HelloWorld{
	private static HelloWorld instance;
	public static void main(String[] args){
	instantiateHelloWorldMainClassAndRun();