Fortran返回语句 [英] Fortran return statement

问题描述

我试图在gfortran下编译一些在g77下编译好的代码。这个问题似乎来自一个return语句：

ffuncs.f：934.13：

  RETURN E 
 1 
  

错误：在（1）需要一个SCALAR-INTEGER返回说明符

在代码中，任何东西E被指定为真实的* 8：

IMPLICIT REAL * 8（A - H，O - Z）

然而，E从来没有被赋予任何价值或事实上，直到返回语句才会看到它。我对fortran几乎一无所知。

谢谢。

解决方案<在FORTRAN中（我非常熟悉Fortran 77）， RETURN n 不用于返回函数值;相反，它会像其他语言中的异常处理一样：退出到正常的代码位置。

您通常会调用这样的一个 SUBROUTINE 或 FUNCTION 标签作为参数，例如

<$ $'$ $ $'$ $ $ $ $ $ $ $ $ $ $ $'$'$ $ $ $'$'$'$'$' 2'

如果MYSUB中出现错误，则您执行 RETURN 1 或 RETURN 2 （而不是普通的RETURN），你可以在调用例程中直接跳到标签998或999。

这就是为什么通常你需要一个返回的整数 - 它不是一个值，而是一个你想要的错误出口的索引。

RETURN E 对我来说听起来不对。除非有一种我不知道的语法，否则以前的编译器应该将其标记为错误。

I'm trying to get some code compiled under gfortran that compiles fine under g77. The problem seems to be from a return statement:

ffuncs.f:934.13:

  RETURN E
         1

Error: Alternate RETURN statement at (1) requires a SCALAR-INTEGER return specifier

In the code anything E was specified as real*8:

IMPLICIT REAL*8 ( A - H , O -Z )

However, E was never given a value or anything in fact you never see it until the return statement. I know almost nothing about fortran. What is the meaning of a return statement with an argument in fortran?

Thanks.

解决方案

In FORTRAN (up to Fortran 77, which I'm very familiar with), RETURN n is not used to return a function value; instead, it does something like what in other languages would be handled by an exception: An exit to a code location other than the normal one.

You'd normally call such a SUBROUTINE or FUNCTION with labels as arguments, e.g.

  CALL MYSUB(A, B, C, *998, *999)
...
998 STOP 'Error 1'
998 STOP 'Error 2'

and if things go wrong in MYSUB then you do RETURN 1 or RETURN 2 (rather than the normal RETURN) and you'd be hopping straight to label 998 or 999 in the calling routine.

That's why normally you want an integer on that RETURN - it's not a value but an index to which error exit you want to take.

RETURN E sounds wrong to me. Unless there's a syntax I'm unaware of, the previous compiler should have flagged that as an error.

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