How to print pthread_t

This will print out a hexadecimal representation of a pthread_t, no matter what that actually is:

void fprintPt(FILE *f, pthread_t pt) {
  unsigned char *ptc = (unsigned char*)(void*)(&pt);
  fprintf(f, "0x");
  for (size_t i=0; i<sizeof(pt); i++) {
    fprintf(f, "%02x", (unsigned)(ptc[i]));
  }
}

To just print a small id for a each pthread_t something like this could be used (this time using iostreams):

void printPt(std::ostream &strm, pthread_t pt) {
  static int nextindex = 0;
  static std::map<pthread_t, int> ids;
  if (ids.find(pt) == ids.end()) {
    ids[pt] = nextindex++;
  }
  strm << ids[pt];
}

Depending on the platform and the actual representation of pthread_t it might here be necessary to define an operator< for pthread_t, because std::map needs an ordering on the elements:

bool operator<(const pthread_t &left, const pthread_t &right) {
  ...
}