A good way to leak your file descriptors is to mix up destructors (as in C++) with finalizers (in systems with garbage collection). The common C++ idiom is resource acquisition is initialisation (aka RAII):

{
  ifstream in(filename);
  // ... do stuff with in ...
}               // file is closed here by in's destructor

So if your system runs out of file descriptors before it runs out of memory, you're leaking fd's.

fd leak /F-D leek/ n.

A kind of programming bug analogous to a core leak, in which a program fails to close file descriptors (`fd's) after file operations are completed, and thus eventually runs out of them. See leak.

--The Jargon File version 4.3.1, ed. ESR, this entry manually entered by rootbeer277.