在/src/io/calc_df.F90中，有许多：
DO WHILE(ASSOCIATED(current))
下面整理一些有关associated的用法。
简单的说associated返回一个逻辑值，用于指针的语法。
ASSOCIATED
Inquiry Intrinsic Function (Generic):
Returns the association status of its pointer argument or indicates whether the pointer is associated with the target.
Syntax
result = ASSOCIATED (pointer [, target])
pointer (Input)
Must be a pointer (of any data type).
target (Optional; input)
Must be a pointer or target.
The pointer (in pointer or target) must not have an association status that is undefined. ???
Results:
The result is a scalar of type default logical.
- If only pointer appears, the result is true if it is currently associated with a target; otherwise, the result is false.
- If target also appears and is a target, if pointer is currently associated with target; otherwise, the result is false.
- If target is a pointer, the result is true if both pointer and target are currently associated with the same target; otherwise, the result is false.
- If either pointer or target is disassociated, the result is false.
如果上面的英文对你来说还不够的话，下面再贴上一个中文的解释（个人感觉更看不懂）。
fortran中有关指针的用法总结（此文来自科学网何林博客）
