I never really liked C's assert() feature. If an assertion is violated, it'll tell you what assertion failed but completely lacks any context:

example: example.c:9: main: Assertion `i == 3' failed.

This is better:

Assertion failed insist.c:7 in main(), insist(i == 3): Something went wrong, wanted i == 3, got 4

The main difference here is that there's context about what failed. A message for humans looking to debug this. This is especially important on Linux these days because every distro I've used recently hates sysadmins and hates debugging - all libraries are stripped of debug symbols and coredumps are disabled by default.

What's the usage look like?

#include 
#include 
#include "insist.h"

int main() {
  int i = 4;
  //assert(i == 3);
  insist(i == 3, "Something went wrong, wanted i == 3, got %d", i);
  return 0;
} 

I also added a special 'return' version of this, 'insist_return' that lets you do error checking and early aborting like this:

insist_return(fd >= 0, START_FAILURE,
              "socket() returned %d, an error: %s", fd, strerror(errno));

Works just like insist() except returns START_FAILURE if 'fd > 0' is false and additionally logs the error formatted above.

Code here: insist.h