Question

I had never thought about this before, but lately I’ve been worried about something. In Fortran90(95), say I create a really big array

Integer :: X(1000000)

and then I write a function that takes this array as an argument. When I pass the array to the function (as in myfunc(X)) what exactly happens during run time?

Does the entire array get passed by value and a new copy constructed inside the function?(costly)
Or does the compiler simply pass some sort of reference or pointer to the array?(cheap)

Do the dimension of the array or the declaration of the function make a difference?

Answer 1

In Fortran 90 , as in most other programming languages, arrays are passed by reference (technically, this is often a reference to the first item of the array). In Fortran 90, non-array values are also usually passed by reference. So, you needn’t worry about the size of the parameters you pass, since they won’t be copied but will, instead, be passed simply by reference.