Formatted IO

List-directed print

List-directed output is the fastest way to see values: print followed by a star and a list prints each item with readable spacing.

You give up layout control, but for debugging and small tools the default spacing is exactly what you want.

program listed implicit none integer :: n real :: price n = 42 price = 2.5 print *, n, price end program listed

./listed

42 2.5000000

Format specs

A format string spells out the layout: A prints text, I5 reserves five slots for an integer, and F6.2 prints a real with two decimals.

Each item in the write list matches one spec in order, so the label, the count, and the price land exactly side by side.

program specs implicit none integer :: n real :: price n = 42 price = 2.5 write(*, "(A, I5, F6.2)") "n=", n, price end program specs

./specs

n= 42 2.50

Widths that fit

Widths must fit the value: I5 gives room to spare, I2 fits 42 exactly, and I1 is too narrow so Fortran prints stars instead.

Stars are a loud hint to widen the field, which beats silent truncation of your numbers every time.

program widths implicit none write(*, "(I5)") 42 write(*, "(I2)") 42 write(*, "(I1)") 42 end program widths

./widths

42
42
*

Star format

The star format means list-directed inside a write statement: write with a star behaves like print and picks spacing for you.

Use it for logs and drafts, then switch to explicit specs when the layout must look polished.

program star implicit none integer :: a integer :: b a = 7 b = 9 write(*, *) a + b print *, a + b end program star

./star

16
16

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Article author: Arthur Isaev