Files
| Open with newunit | |
| Read records | |
| Write records | |
| Close and status |
Open with newunit
Open connects a variable to a file: newunit hands you a free unit number, file names the path, and status replace starts fresh.
Action write locks in your intent, so a later accidental read fails loudly instead of corrupting data.
program openfile
implicit none
integer :: u
open(newunit=u, file="nums.txt", status="replace", action="write")
write(u, *) 42
close(u)
end program openfile
Read records
Reading mirrors writing: open with status old and action read, pull values with a matching read list, then close.
Status old demands that the file exists, which catches typos in the name before any data moves.
program readrec
implicit none
integer :: u
integer :: n
open(newunit=u, file="nums.txt", status="old", action="read")
read(u, *) n
close(u)
print *, n
end program readrec
./readrec
42
Write records
Formatted writes control each record: one write statement produces one line, and the format sets its look.
Here a loop writes 1, 2, and 3 on separate lines, each in a field three wide.
program writerec
implicit none
integer :: u
integer :: i
open(newunit=u, file="count.txt", status="replace", action="write")
do i = 1, 3
write(u, "(I3)") i
end do
close(u)
end program writerec
cat count.txt
1
2
3
Close and status
Close releases the unit, and its status decides the fate of the file: keep saves it while delete removes a scratch file at once.
Always close what you open: open units block other access, and unwritten buffers may never reach the disk.
program closestat
implicit none
integer :: u
open(newunit=u, file="temp.txt", status="replace", action="write")
write(u, *) "done"
close(u, status="keep")
end program closestat
Next: Subroutines and functions
Article author: Arthur Isaev
