Same as the fgetc function, except used only within a scope
    protected by flockfile and funlockfile.

    This function is supported on OpenVMS Integrity servers and
    Alpha only.

    Format

      #include  <stdio.h>

      int fgetc_unlocked  (FILE *file_ptr);

1 - Argument

 file_ptr

    A file pointer.

2 - Description

    The reentrant version of the fgetc function is locked against
    multiple threads calling it simultaneously. This incurs overhead
    to ensure integrity of the stream. The unlocked version of this
    call, fgetc_unlocked can be used to avoid the overhead. The
    fgetc_unlocked function is functionally identical to the fgetc
    function, except that fgetc_unlocked can be safely used only
    within a scope that is protected by the flockfile and funlockfile
    functions used as a pair. The caller must ensure that the stream
    is locked before fgetc_unlocked is used.

    Compiling with the __UNIX_PUTC macro defined enables an
    optimization that uses a faster, inlined version of this
    function.

    See also getc_unlocked, flockfile, ftrylockfile, and funlockfile.

3 - Return Values

    n                  The returned character.
    EOF                Indicates the end-of-file or an error.