snipplets.dev/code/C/System/get_ram_usage.c

#include <sys/resource.h>
#include <stdio.h>

int main() {
  struct rusage r_usage;
  getrusage(RUSAGE_SELF, &r_usage);

  printf("Memory usage: %ld kilobytes\n", r_usage.ru_maxrss);

  return 0;
}