By default, a data transfer leaves the file positioned after
the last record read or written. This type of I/O is called
advancing. Fortran 90 also allows nonadvancing I/O, which
positions the file just after the last character read or written,
without advancing to the next record. It is character-oriented and
can be used only with external files opened for sequential access.
It cannot be used with list-directed or namelist-directed I/O.
To use nonadvancing I/O, you must specify ADVANCE='NO'
in the READ or
WRITE statement.
The example program in “File access” uses nonadvancing I/O in the
first WRITE statement,
which is reproduced here:
WRITE (6, FMT="(A)", ADVANCE="NO") &
" Enter number to insert in list: " |
The effect of nonadvancing I/O on the WRITE
statement is to suppress the newline character that is normally
output at the end of a record. This is the desired effect in the
example program: by using a nonadvancing WRITE
statement, the user input to the READ
statement stays on the same line as the prompt.
You can get the same effect with the newline ($)
edit descriptor, an HP Fortran 90 extension that also suppresses
the carriage-return/linefeed sequence at the end of a record;
see “Newline ($) edit descriptor”.
For an example program that illustrates nonadvancing I/O
in a READ statement,
see “Nonadvancing I/O”. For more
information about nonadvancing I/O and the ADVANCE=
specifier, see the READ
and WRITE statements
in Chapter 10.
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