I am new to fortran and I am having issues trying to pass in a argument via command line. For instance my working code has the following lines:
!experimental parameters
real (kind=8), parameter :: rhot =1.2456
!density of top fluid
real (kind=8), parameter :: rhob = 1.3432
!density of bottom fluid
real (kind=8), parameter :: rhof = (rhot-rhob)
!generic function of rhot rhob
And I would like to hand them in via:
./fulltime_2009_05_15_Fortran9 [Value rhot] [Value rhob]
using something like:
call get_command_argument(1,input1)
call get_command_argument(2,input2)
read(input1,*) rhot
read(input2,*) rhob
The issue is, I declare parameters like rhof that depend on the inputted values. So I would like to have the user inputted values applied immediately so that all dependent parameters can use those values. However, if modify my code to be:
real (kind=8) :: rhot, rhoB
call get_command_argument(1,input1)
call get_command_argument(2,input2)
read(input1,*) rhot
read(input2,*) rhob
real (kind=8), parameter :: rhof = (rhot-rhob)
I get the error: A specification statement cannot appear in the executable section.
Any thoughts or suggestions for how I could address this issue?
A compile time constant (parameter) cannot be changed by command line arguments. It is fixed at compile time.
This code:
real (kind=8) :: rhot, rhoB
real (kind=8) :: rhof
call get_command_argument(1,input1)
call get_command_argument(2,input2)
read(input1,*) rhot
read(input2,*) rhob
rhof = (rhot-rhob)
would compile fine. But you cannot have a variable declaration after a normal statement.
You could have
real (kind=8) :: rhot, rhoB
call get_command_argument(1,input1)
call get_command_argument(2,input2)
read(input1,*) rhot
read(input2,*) rhob
block
real (kind=8) :: rhof = (rhot-rhob)
in Fortran 2008, but you cannot define a compile-time constant using a non-constant expression.
Some programming langauges do allow a type of constants that are set during the configuration of the run and are fixed thereafter. Fortran is not one of them.