Fortran：整数* 4与整数（4）与整数（种类= 4） [英] Fortran: integer*4 vs integer(4) vs integer(kind=4)

问题描述

我试图学习Fortran，我看到很多不同的定义被传递，我想知道他们是否试图完成同样的事情。以下是什么区别？

• 整数* 4


• integer（4）


• integer（kind = 4） 90中，最好的方法是使用内部函数指定你需要的精度 - 这保证了可移植性和你得到你需要的精度。例如，要获得将支持至少8位小数位的整数i和my_int，可以使用：
  
  

    integer，参数： ：RegInt_K = selected_int_kind（8）
   integer（kind = RegInt_K）:: i，my_int 
    

  将RegInt_K（或您选择的任何名称）定义为参数后，您可以在整个代码中将其用作符号。这也很容易改变精度。

  
  
  

  请求8或9位十进制数字通常会得到一个4字节的整数。

  
  
  

  整数* 4是一个常见的扩展，它返回到旧的FORTRAN来指定一个4字节的整数。
  
  

  整数（4）或整数（RegInt_K）是整数（kind = 4）或整数（kind = RegInt_K）的缩写。整数（4）与整数* 4不同并且不可移植 - 语言标准没有指定种类的数值。大多数编译器对于4字节整数使用kind = 4，对于这些编译器，integer * 4和integer（4）将提供相同的整数类型 - 但也有例外，因此整数（4）是不可移植的并且最好避免。
  
  

  reals的方法类似。

  
  
  

  更新：如果您不想指定数字类型按要求的精度，而是通过他们将使用的存储，Fortran 2008提供了一种方法。 reals和整数可以用使用 ISO_FORTRAN_ENV 模块之后的存储位数来指定，例如for一个4字节（32位）整数：
  
  

   使用ISO_FORTRAN_ENV 
  整数（int32）:: MyInt 
    

  gfortran手册在内部模块下有文档。

  
  

  I'm trying to learn Fortran and I'm seeing a lot of different definitions being passed around and I'm wondering if they're trying to accomplish the same thing. What is the difference between the following?

  • integer*4
  • integer(4)
  • integer(kind=4)

  解决方案

  In Fortran >=90, the best approach is use intrinsic functions to specify the precision you need -- this guarantees both portability and that you get the precision that you need. For example, to obtain integers i and my_int that will support at least 8 decimal digits, you could use:

  integer, parameter :: RegInt_K = selected_int_kind (8)
  integer (kind=RegInt_K) :: i, my_int
  

  Having defined "RegInt_K" (or whatever name you select) as a parameter, you can use it throughout your code as a symbol. This also makes it easy to change the precision.

  Requesting 8 or 9 decimal digits will typically obtain a 4-byte integer.

  integer*4 is an common extension going back to old FORTRAN to specify a 4-byte integer.

  integer (4) or integer (RegInt_K) are short for integer (kind=4) or integer (kind=RegInt_K). integer (4) is not the same as integer*4 and is non-portable -- the language standard does not specify the numeric values of kinds. Most compilers use the kind=4 for 4-byte integers -- for these compilers integer*4 and integer(4) will provide the same integer type -- but there are exceptions, so integer(4) is non-portable and best avoided.

  The approach for reals is similar.

  UPDATE: if you don't want to specify numeric types by the required precision, but instead by the storage that they will use, Fortran 2008 provides a method. reals and integers can be specified by the number of bits of storage after useing the ISO_FORTRAN_ENV module, for example, for a 4-byte (32-bit) integer:

  use ISO_FORTRAN_ENV
  integer (int32) :: MyInt
  

  The gfortran manual has documentation under "intrinsic modules".

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