Octave's C-style input and output functions provide most of the functionality of the C programming language's standard I/O library. The argument lists for some of the input functions are slightly different however because Octave has no way of passing arguments by reference.
In the following file refers to a file name and fid refers
to an integer file number as returned by fopen.
There are three files that are always available. Although these files can be accessed using their corresponding numeric file ids you should always use the symbolic names given in the table below since it will make your programs easier to understand.
| stdin | Built-in Variable |
| The standard input stream (file id 0). When Octave is used interactively this is filtered through the command line editing functions. |
| stdout | Built-in Variable |
| The standard output stream (file id 1). Data written to the standard output is normally filtered through the pager. |
| stderr | Built-in Variable |
| The standard error stream (file id 2). Even if paging is turned on the standard error is not sent to the pager. It is useful for error messages and prompts. |