Endianess is important to know. This C function will help you with detecting it.

endianess.c

/*******************************************************************
 * Sometimes you need to figure out which endianess the machine
 * runs on. C on its own doesn't have any form of endianess
 * detection. But using unions can actually be useful to detect
 * endianess. Sometimes you need to detect endianess to save
 * a binary file in a correct format. Because by default
 * the machine uses whichever endianess it operates to save files.
 * Which makes the files not transferable between machines that
 * use differet endianess. Detecting the endianess is crucial
 * so you can swap endianess for file saving AND loading if needed.
 *
 * Unions are like structs, with the difference being all items
 * share the same memory space. Size of the union is determined
 * by the largest item in the union. So if you have an int and char
 * in a union, the union will take up 4 bytes in memory, because
 * int is 4 bytes large, and char is 1 byte large. If it was
 * a struct, then it would take up 5 bytes (since struct items
 * do not share the same memory space).
 * 
 * Endianess determines how multi-byte values are stored in memory.
 * Little endian means the least significant byte will be stored
 * earlier in memory than the most significant bit. For big endian,
 * it reverses. So if you put number value "1" in an int of a union,
 * then what is gonna be stored in the char of a union depends on
 * the endianess of the machine. That means we can use the unions
 * to our advantage to detect endianess. Let's do that.
 *******************************************************************/
#include <stdio.h>
#include <stdbool.h>

union endian {
  int i;
  char c;
};

bool __is_little_endian() {
  union endian det;
  det.i = 1;
  
  return (bool) det.c;
}

int main() {
  if(__is_little_endian())
    fprintf(stdin, "Machine is little endian\n");
  else
    fprintf(stdin, "Machine is big endian\n");
  
  return 0;
}