find_next_id.cpp

#include <dirent.h>
#include <fstream>
#include <libgen.h>
#include <stdio.h>

int main(void) {
  int maxidx = 0;
  DIR *dir;
  struct dirent *ent;
  const char *base_filename = "queries.log";
  const char *datadir = "log";

  size_t efl = strlen(base_filename);
  if ((dir = opendir(datadir)) != NULL) {
    while ((ent = readdir(dir)) != NULL) {
      if (strlen(ent->d_name) == efl + 9) {
        if (strncmp(ent->d_name, base_filename, efl) == 0) {
          if (ent->d_name[efl] == '.') {
            int idx = atoi(ent->d_name + efl + 1);
            if (idx > maxidx)
              maxidx = idx;
          }
        }
      }
    }
    closedir(dir);
  } else {
    /* could not open directory */
    printf("Unable to open datadir: %s\n", datadir);
    exit(EXIT_FAILURE);
  }

  printf("Current ID is %i\n", maxidx);
}