Stream States


The new home for Visual Studio documentation is Visual Studio 2017 Documentation on

The latest version of this topic can be found at Stream States.

The valid states, and state transitions, for a stream are shown in the following figure.


Each of the circles denotes a stable state. Each of the lines denotes a transition that can occur as the result of a function call that operates on the stream. Five groups of functions can cause state transitions.

Functions in the first three groups are declared in <stdio.h>:

Functions in the remaining two groups are declared in <wchar.h>:

The state diagram shows that you must call one of the position functions between most write and read operations:

  • You cannot call a read function if the last operation on the stream was a write.

  • You cannot call a write function if the last operation on the stream was a read, unless that read operation set the end-of-file indicator.

Finally, the state diagram shows that a position operation never decreases the number of valid function calls that can follow.

Files and Streams