f = open("/path/to/file"); // do something with file vs. d = opendir("path/to") while((dent = readdir(d)) != NULL) { if(!dent.name.startsWi

f = open("/path/to/file"); // do something with file vs. d = opendir("path/to") while((dent = readdir(d)) != NULL) { if(!dent.name.startsWith("file")) continue; // do something with first matched entry } The former is O(log n) on ext4, O(n) on older filesystems that use flat lists. The latter is always O(n)