Real kinds in Fortran

One third at 32 and 64 bits: iso_fortran_env names the precisions portably.

program real_kinds
    ! iso_fortran_env names the kinds portably: real32, real64.
    use iso_fortran_env, only: real32, real64
    implicit none
    real(real32) :: single = 1.0_real32 / 3.0_real32
    real(real64) :: double = 1.0_real64 / 3.0_real64

    print *, "single: ", single
    print *, "double: ", double
    print *, "epsilon at 32 bits: ", epsilon(single)
    print *, "epsilon at 64 bits: ", epsilon(double)
    print *, "largest double:     ", huge(double)
end program real_kinds

How it works

1. use iso_fortran_env, only: real32, real64 imports the kind constants.
2. 1.0_real64 stamps the kind on the literal, not just the variable.
3. epsilon and huge report each kind's precision and ceiling.

Keywords and builtins used here

• end
• epsilon
• huge
• implicit
• none
• only
• print
• program
• real
• use

The run, in numbers

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Type this snippet

Step 1 of 3 in Kinds & modules, step 22 of 27 in Language basics.

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