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  Fortran allocatable derived types

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• Debanjan Mukherjee October 28, 2011 11:11 AM PDT    Derived data types with allocatable components Hello, I think I have some flaws in my understanding of the derived data types and how the memory allocation happens for them. I am currently working on a problem where I have to create some form of a list with variable number of entries, and I am trying to create a data type for that using allocatable components as follows: type boxList integer, dimension(:), allocatable:: boxTuples integer, dimension(:), allocatable:: boxMembers end type boxList type(boxList), dimension(:),allocatable:: myboxList 1. One of the reasons why I wanted to have the components allocatable - is because I was intending on  performing something like a 'push_back()' operation in C++ on my vector boxMembers to keep adding entries. But that leavse me with an allocatable array of derived types with allocatable components - and I am not sure how the memory assignment works here. 2. Could I first allocate the array myboxList and then for each list - I go in and allocate the individual members ? 3. Also, is there any way in which I can define a constant number at runtime - something like ./executible.out "constant-number" like we can do with c++ codes ? I ask this because if so, then I can fix the dimension of one of the member vectors by writing for example ./executible.out 3 for a 3 dimensional problem - (effectively for my physics simulator, this is the number of space dimensions I am working with). I guess this would be the equivalent of main(int argc) or something. Any pointers will be very helpful to aid my understanding of these derived types. Thank you. Steve Lionel (Intel) October 28, 2011 12:58 PM PDT Rate   #1 Derived data types with allocatable components When you have an array of derived types with allocatable components, yes you need to allocate the parent array first and then allocate the components.  I am not familiar with push_back in C++.  I will note that you can simply assign to allocatable arrays and have the allocation happen automatically if you add -standard-semantics. I don't know how you do what you're discussing in C++ - it sounds to me as if you have something that reads the argument list.  This is hardly a "constant".  But you can obtain a value from the argument list (as a string) using GET_COMMAND_ARGUMENT and then decode it as you wish, then use the value in an ALLOCATE statement. Steve Attaching or including files in a post Doctor Fortran blog @DoctorFortran on Twitter

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