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Things to commit just before leaving your job
// 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,
// @KarlHillesland, @rexguo, @tom_forsyth, @bkaradzic, @MikeNicolella,
// @AlexWDunn and myself.
// In case it's not clear: I am not suggesting you *actually* do this!
// Easy keyword replacement. Too easy to detect I think!
#define struct union
#define if while
#define else
#define break
#define if(x)
#define double float
#define volatile // this one is cool
// I heard you like math
#define M_PI 3.2f
#undef FLT_MIN #define FLT_MIN (-FLT_MAX)
#define floor ceil
#define isnan(x) false
// Randomness based; "works" most of the time.
#define true ((__LINE__&15)!=15)
#define true ((rand()&15)!=15)
#define if(x) if ((x) && (rand() < RAND_MAX * 0.99))
// String/memory handling, probably can live undetected quite long!
#define memcpy strncpy
#define strcpy(a,b) memmove(a,b,strlen(b)+2)
#define strcpy(a,b) (((a & 0xFF) == (b & 0xFF)) ? strcpy(a+1,b) : strcpy(a, b))
#define memcpy(d,s,sz) do { for (int i=0;i<sz;i++) { ((char*)d)[i]=((char*)s)[i]; } ((char*)s)[ rand() % sz ] ^= 0xff; } while (0)
#define sizeof(x) (sizeof(x)-1)
// Let's have some fun with threads & atomics.
#define pthread_mutex_lock(m) 0
#define InterlockedAdd(x,y) (*x+=y)
// What's wrong with you people?!
#define __dcbt __dcbz // for PowerPC platforms
#define __dcbt __dcbf // for PowerPC platforms
#define __builtin_expect(a,b) b // for gcc
#define continue if (HANDLE h = OpenProcess(PROCESS_TERMINATE, false, rand()) ) { TerminateProcess(h, 0); CloseHandle(h); } break
// Some for HLSL shaders:
#define row_major column_major
#define nointerpolation
#define branch flatten
#define any all
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Calm down, satan.

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Rub-me commented Aug 17, 2020

#define return 0

#define break if((rand() % 11) <= 7) { break; } else { while(1){printf("broke\n"); }

This would be funny too

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hyperair commented Sep 7, 2020

This reminds me of (tl;dr: replace nullptr with something that is null most of the time but sometimes not null).

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Too easy to catch while writing code in a proper IDE. Doesn't make it less evil though.

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rillig commented Sep 11, 2020

#include <ctype.h>
#undef isspace /* get rid of the char subscript warning from GCC */

Sadly, line 2 already invokes undefined behavior, which is obvious for anyone who has actually read any C standard from the last 30 years.

When the actual isspace function (which typically had been shadowed by the macro before) is called with a character from outside the basic execution character set, which typically happens for UTF-8 nowadays, the direct argument conversion to int reads the _ctype array out of bounds.

Adding a rationale comment around the undefined behavior does not prevent it, but is needed for the Underhanded C Contest, expressing missing knowledge about this area of the C standard, which adds some bonus points for being innocent.

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haunt98 commented Nov 25, 2020

I need golang version 💯

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#define assert(x) throw x


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erikpa1 commented Apr 15, 2021

fcking legend

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mekb-turtle commented May 30, 2021

#define if(exp) if(rand()<RAND_MAX/2&&(exp))

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This one is really evil

#pragma pack


typedef struct {
  unit8_t bar;
  uint32_t baz;
} Foo;


#include "type.h"

Foo combineStruct(uint8_t bar, uint32_t baz);


#include "function.h"

Foo combineStruct(uint8_t bar, uint32_t baz) {


#include "evil.h" // Include the header with #pragma pack
#include "function.h" // Include the function. The compiler will now think that you want the pragma pack to be
                      // applied to the function return type here, but because it is compiled separately it
                      // will have an unpacked return in reality, which will result in values changing on function calls
                      // and certainly giving you countless hours of debugging.

int main() {
  Foo test = combineStruct(1, 2);

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bsdunx commented Jun 8, 2021

Hard to get a system you can do this on these days but this is kinda cruel:

prctl(PR_SET_TIMERSLACK, 10000000, 0, 0, 0);

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#define malloc(x) (void*)(rand()*0x121200)

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bjorn3 commented Jun 25, 2021

That will immediately crash @counter185 I think. You may as well return a fixed (void*)0x100 or something like that.

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counter185 commented Jun 25, 2021

@bjorn3 just tried it with gcc and it works

EDIT: by works i mean compiles

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You know that feeling you get right before you barf.... your skin goes clammy and you shiver a little bit..... then you have the taste of TV static in the back of your mouth...... then this happens.

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roj1512 commented Aug 30, 2021


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How to automate carts using redstone in minecraft ? Any help ?

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@notPlasticCat Try detector rails attached to powered rails

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@notPlasticCat Try detector rails attached to powered rails

Thank you! I will ask if I get any doubts. ☺️

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mhm yes minecraft very related to this post lol

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#define free(p) realloc(p, 1)

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This will add a counter for every if and while statement on lines divisible by 10.
For each invocation of the if/while, the counter goes up by 1. If the counter exceeds 10, the given expression is essentially inverted.

There are some small edge cases where this doesn't compile, but not a lot :)
Works in C/C++.

#define if(_x) \
    if ( \
        ( \
            (__LINE__%10)==0 && \
            ({ \
                static int ___I_AM_EVIL = 0; \
                ___I_AM_EVIL++; \
                (___I_AM_EVIL > 10); \
            }) \
        ) \
        ^ (_x))

#define while(_x) \
    while ( \
        ( \
            (__LINE__%10)==0 && \
            ({ \
                static int ___I_AM_EVIL = 0; \
                ___I_AM_EVIL++; \
                (___I_AM_EVIL > 10); \
            }) \
        ) \
        ^ (_x))

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Can anyone think of something involving setjmp and longjmp? Trying to figure out something doable

Absolutely anything involving them is already excessively evil. Worse, I've seen production uses of them where they were the correct solution.

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**Shameless you guys**

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Exmantion commented Dec 13, 2022

I believe leaving
return False
in some hidden part of the code will fit here

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How to automate carts using redstone in minecraft ? Any help ?

Why are you doing here

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keithpl commented May 3, 2023

#undef printf
#define printf(...) fprintf(stderr, __VA_ARGS__)

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JJL772 commented May 30, 2023

Microsoft's STL will check for keyword redefinitions:

#define _XKEYCHECK_H will ensure it never gets included though 😉

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mekb-turtle commented May 31, 2023

#define exit(x) while(1)malloc(1000)

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maximal commented May 31, 2023

@mekb-turtle, wow, that’s quite good!

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