12.4: File Read

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The file must be opened for “read” or “readwrite” access before any information can be read from the file. The general form of the write statement is as follows:

read (unit=<unit number>, fmt=<format statement>,    &
            iostat=<variable>) <variables>

The read is the same as the simple read; however, the unit number must be the number assigned during the open operation. If the status variable is set to less than 0, that is an indication that the end of the file has been reached. For example, if the file numbers.dat exists and has two numbers (on separate lines), the following declarations,

integer :: num1, num2, myopenstatus, myreadstatus
character(11) :: myfilename="numbers.txt"

and the following Fortran statements,

open (unit=12, file=myfilename, status="old",    &
            action="read", position="rewind",    &
            iostat=myopenstatus)
if (myopenstatus > 0) stop "Cannot open file."

read (12, '(i5)', iostat=myreadstatus) num1
read (12, '(i5)', iostat=myreadstatus) num2

would read information from the file.