Fortran 中的 CPP 预处理语句可以缩进吗? [英] Can CPP preprocessing statement in Fortran be indented?

问题描述

我对使用 Fortran 预处理语句还很陌生，并且有一个可能非常原生的问题.Fortran 预处理语句可以缩进吗?我在 Linux (openSUSE Leap) 上使用 Gfortran 4.8.1 进行了测试，结果发现它根本不能缩进.

I am fairly new to use Fortran preprocessing statement and have a question which is probably pretty native. Can Fortran preprocessing statement be indented? I tested using Gfortran 4.8.1 on Linux (openSUSE Leap) and it turned out I it can not be indented at all.

以下代码 main.f90 与 gfortran -cpp main.f90 -o main 一起使用:

The following code main.f90 works with gfortran -cpp main.f90 -o main:

program main
    implicit none
#ifdef DEBUG
    print *, "I am in debug mode"
#endif 
    print *, "hello world!"
end program main

但是下面会报错:

program main
    implicit none
    #ifdef DEBUG
    print *, "I am in debug mode"
    #endif 
    print *, "hello world!"
end program main

错误消息是 Error: Invalid character in name at (1).这是否意味着我们应该始终从行首开始编写预处理语句，或者它只是编译器特定的规则?任何帮助将不胜感激，并提前致谢！

The error message is Error: Invalid character in name at (1). Does this mean that we should always write the preprocessing statement from the first beginning of the line or it is just a compiler specific rule? Any help would be greatly appreciated and thanks in advance!

推荐答案

不，它们不能缩进，因为 gfortran 在 传统模式，不允许缩进.它们必须始终从第一列开始.

No, they cannot be indented because gfortran runs CPP in traditional mode which does not allow indentation. They must always start in the first column.

您可以手动运行 CPP，但要非常小心.如果您在某处使用 // 字符串连接运算符，预处理器会将其视为注释.您必须使用@ewcz 在他/她的答案中显示的 -C 标志，该标志禁止丢弃评论.

You could run CPP manually, but be very very careful about that. If you use the // string concatenation operator somewhere the preprocessor would treat it as a comment. You must use the -C flag as shown by @ewcz in his/her answer which disables discarding of comments.

一些编译器提供他们自己的 FPP 预处理器，其行为不同.

Some compilers supply their own FPP preprocessor which behaves differently.

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