ISO_FORTRAN_ENV 或 -fdefault-real-8 将实数提升为双精度 [英] ISO_FORTRAN_ENV or -fdefault-real-8 to promote reals to double precision

问题描述

我一直在使用 gfortran 的 -fdefault-real-8 选项来自动提升在程序到双精度，连同任何常数，例如 1.23.如果我想切换回单精度，我只需要删除该选项并重新编译，而无需更改源代码中的单个字符.

I've always been using the -fdefault-real-8 option of gfortran to automatically promote every single REAL declared anywhere in the program to double precision, along with any constant, e.g. 1.23. If I ever wanted to switch back to single precision, I only had to remove that option and recompile, without changing a single character in the source code.

我开始使用 ISO_FORTRAN_ENV 模块，因为它允许我使用 INPUT|OUTPUT|ERROR_UNIT 等常量，以及 IOSTAT_END 和 IOSTAT_EOR 和其他人(这似乎是朝着可移植性方向发展的一个好而简单的举措，我错了吗?).从那时起，我一直看到并忽略以下警告

At a point I started using ISO_FORTRAN_ENV module, since it allows me to use constants like INPUT|OUTPUT|ERROR_UNIT, as well as IOSTAT_END and IOSTAT_EOR and others (which seemed to be a good and easy move in the direction of portability, am I wrong?). From then on, I've been seeing and ignoring the following warning

Warning: Use of the NUMERIC_STORAGE_SIZE named constant from intrinsic module ISO_FORTRAN_ENV at (1) is incompatible with option -fdefault-real-8

因为到目前为止这种不兼容似乎没有任何影响.

since such incompatibility seems to have no effect so far.

现在，如果可能且值得的话，我想去掉这个警告.

Now I'd like to get rid of this warning if it is possible and worth it.

如果我理解正确，为避免此警告，我应该放弃 -fdefault-real-8 选项并将每个 REAL 更改为 REAL(real64) 和/或到 REAL(dp)(前提是，在后者在这种情况下，将语句 USE, INTRINSIC :: ISO_FORTRAN_ENV, dp => real64 放在该单元中)，这对于 sed 或 vim 来说并不困难.

If I correctly understood, to avoid this warning I should give up on -fdefault-real-8 option and change every REAL to REAL(real64) and/or to REAL(dp) (provided that, in the latter case, the statement USE, INTRINSIC :: ISO_FORTRAN_ENV, dp => real64 is put in that unit), which is not a difficult task for sed or vim.

不过，在我看来，这种更改与使用 -fdefault-real-8 选项不同，因为 所有常量都将保持单精度只要我不向他们添加 d0 .假设 -fdefault-real-8 选项被删除并且 ISO_FORTRAN_ENV 在任何地方使用，有没有办法让程序中的任何常量表现因为每个都有 d0 后缀?无论这是否可能，我是否正确推断我可以将以下几行放在一个模块中，所有其他程序单元都使用该模块，然后每个模块都可以使用 dp 作为种类类型参数?

Nevertheless, it seems to me that this change wouldn't be the same as using -fdefault-real-8 option, since all constants would stay single precision as long as I don't add d0 to them. Assumed the -fdefault-real-8 option is removed and ISO_FORTRAN_ENV is used anywhere, is there any way to make any constant across the program behave as each had d0 suffix? Whether or not this is possible, have I correctly extrapolated that I can put the following lines in a single module which is used by all others program units, each of which can then use dp as kind type parameter?

USE, INTRINSIC :: ISO_FORTRAN_ENV
INTEGER, PARAMETER :: dp = real64

我更喜欢这种方式，因为我可以通过仅更改该行来切换到 real32 或 real128 或其他任何方式.

I would prefer this way since I could switch to real32 or real128 or whatever by changing only that line.

推荐答案

如果你只想让警告静音，而不关心 -fdefault-real-8 对存储关联的影响和一些 Fortran 标准要求，只是不要从模块中导入 NUMERIC_STORAGE_SIZE.例如，

If you just want to silence the warning and you do not care about the implications -fdefault-real-8 has on storage association and some Fortran standard requirements, just do not import NUMERIC_STORAGE_SIZE from the module. For example,

USE, INTRINSIC :: ISO_FORTRAN_ENV, only: INPUT_UNIT,OUTPUT_UNIT,ERROR_UNIT

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