Monkey patching in C (Linux/Unix)

libmyrand.c

/*
 * Let's redefine rand() by simply compiling creating an position-independent object code:
 * $ gcc -c -fPIC libmyrand.c -o libmyrand.o
 * 
 * Then create a shared library object from it:
 * $ gcc libmyrand.o -shared -o libmyrand.so
 *
 * As a last step, load this dynamic library, so the dynamic linker will link this rand(),
 * instead of the one inside the standard library:
 * $ export LD_PRELOAD=./libmyrand.so
 *
 * After this every, program using rand() will be using our function. :)
*/
int rand(void)
{
  return 4; // chosen by a fair dice roll.
}
// https://xkcd.com/221/

myrandtest.c

/* 
 * Compile this via:
 * $ gcc myrandtest.c -o myrandtest
 * 
 * Test the monkey patching, by setting and unsetting LD_PRELOAD as mentioned previously:
 * $ ./myrandtest
 * $ export LD_PRELOAD=./libmyrand.so
 * $ ./myrandtest
*/
#include <stdio.h>
#include <time.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
  printf("Seeding by time...\n");
  srand(time(NULL));

  int i;
  for (i = 0; i < 10; i++) {
    printf("%d\n", (int)rand());
  }
  return EXIT_SUCCESS;
}