带指针的Fortran函数可正常分配 [英] Fortran Functions with a pointer result in a normal assignment

问题描述

在对这里的问题进行了一些讨论之后在Fortran中正确执行Final例程 我认为了解带指针结果的函数何时适合与常规或指针分配一起使用将很有用.例如，鉴于此简单功能

After some discussion on the question found here Correct execution of Final routine in Fortran I thought it will be useful to know when a function with a pointer result is appropriate to use with a normal or a pointer assignment. For example, given this simple function

 function pointer_result(this)
 implicit none 
 type(test_type),intent(in) pointer :: this 
 type(test_type), pointer :: pointer_result 

 allocate(pointer_result)
 end function 

我通常会执行test=>pointer_result(test)，其中已经使用pointer属性声明了test.正常分配test=pointer_result(test)是合法的，但这意味着有所不同.

I would normally do test=>pointer_result(test), where test has been declared with the pointer attribute. While the normal assignment test=pointer_result(test) is legal it means something different.

与指针分配相比，普通分配意味着什么?

What does the normal assignment imply compared to the pointer assignment?

什么时候使用一个或另一个分配有意义?

When does it make sense to use one or the other assignment?

推荐答案

常规作业

test = pointer_result()

表示test的当前目标的值将被结果指针指向的值覆盖.如果test指向某个无效地址(未定义或为null)，程序将崩溃或产生未定义的结果.该函数分配的匿名目标将不再有指向它的指针，并且内存将被泄漏.

means that the value of the current target of test will be overwritten by the value pointed to by the resulting pointer. If test points to some invalid address (is undefined or null) the program will crash or produce undefined results. The anonymous target allocated by the function will have no pointer to it any more and the memory will be leaked.

几乎没有合法用途，但是当人们打错字并写=而不是=>时，很可能会发生这种情况.这是一种非常容易制作的方法，并且有几种样式指南建议从不使用指针函数.

There is hardly any legitimate use for this, but it is likely to happen when one makes a typo and writes = instead of =>. It is a very easy one to make and several style guides recommend to never use pointer functions.

这篇关于带指针的Fortran函数可正常分配的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！