C: What is a/example of a buffer underflow? -

I know what an buffer overflow is what I do not know what Buffer Underflow .

I'm guessing that when the overflow of a specific buffer bytes is obtained, instead of an underflow of bytes.

  four buffers [8]; Fgets (buffer, size (buffer), staden);   
 The above will not make any errors.  
  Four buffer_overflow [8]; Fast (buffer-overflow, 16, studin);   
 The above result was  buffer overflow  if the user was in the input, for example "deutschland"  
 Could I get an example in the code, what is the  buffer underflow ?   
 
 
 There is no buffer underflow directly related to a buffer overflow though, buffer underflow, with one example The problem may be ring buffers.  
 For example, consider audio playback: Your audio buffer possibly has a ring buffer somewhere in the kernel memory. If you write data slowly with the buffer audio driver / hardware than the buffer, then the buffer is empty ( "Underflow"), which causes the stutoring audio to play. Other types of real-time data processing and media playback are also present.  
 Thus buffer underflow is often not a mistake situation (unlike buffer overflow, which usually causes the program to undefine, such as unwanted behaviors such as termination, execution of some unwanted codes, and so on Kind).