// Borrowed from https://github.com/b-k/21st-Century-Examples
#include <stdio.h>
#include <stdlib.h> //abort

/** Set this to \c 's' to stop the program on an error.
  Otherwise, functions return a value on failure.*/
char error_mode;

/** To where should I write errors? If this is \c NULL, write to \c stderr. */
FILE *error_log;

#define Stopif(assertion, error_action, ...) {                    \
	if (assertion){                                           \
		fprintf(error_log ? error_log : stderr, __VA_ARGS__); \
		fprintf(error_log ? error_log : stderr, "\n");        \
		if (error_mode=='s') abort();                         \
		else                 {error_action;}                  \
	} }