传递字符串以在Fortran子例程中执行

问题描述

在下面的子例程中，我想传递一个名为 str 的字符串变量。如果它是'poly'，'gaus'，'slat'，那么它有一个预定义的动作（ fval = 参见下面的代码）。我希望让用户指定一个函数来使用并将其作为字符串变量传递。

这就是...

如果 str ='3 * cos（i * t）'，那么我想要 fval 等于 3 * cos（i * t）。

 子程序f（fval，i， t，str）
隐式无
整数，参数:: ikind = selected_int_kind（8）
整数，参数:: dbl = selected_real_kind（15,307）
 
整数kind = ikind）:: i 
 real（kind = dbl）:: fval，t 
 character str * 100 
 
 if（str .eq。'poly'）then 
 fval = t ** i 
 elseif（str .eq。'slat'）then 
 fval = exp（-i * t）
 elseif（str .eq。'gaus' ）然后
 fval = exp（-i * t * t）
 else 
 fval = ??? 
 endif 
 
结束子程序
  

解决方案

你不能。不容易。但您可以做两件事：

• 首先，您可以使用函数指针。 有一个简单的例子 - 这个想法是，你可以传递在别处定义的函数的名称。这可能足以解决您的问题。




• 您可以调用一个库来解析字符串并评估表达式。我不知道fortran中的任何东西，但是你的Fortran编译器可能支持调用c例程。对于gfortran（也可能是其他人）来说，这看起来好像会起作用 - （例如Fortran代码位于）

In the following subroutine I would like to pass a string variables named str. If it is 'poly', 'gaus', 'slat', then it has a predefined action (fval = see code below ). I would like to have the user specify a function to use and pass that as a string variable.

That is ...

If str = '3*cos(i*t)', then i would like to have fval be equal to 3*cos(i*t). How can I get Fortran to interpret the string entered as a command to be executed by Fortran?

subroutine f(fval, i, t, str)
implicit none
integer, parameter :: ikind = selected_int_kind(8)
integer, parameter :: dbl = selected_real_kind(15,307)

integer(kind = ikind) :: i
real(kind = dbl) :: fval, t
character str*100

if(str .eq. 'poly') then
    fval = t**i
elseif(str .eq. 'slat') then
    fval = exp(-i*t)
elseif(str .eq. 'gaus') then
    fval = exp(-i*t*t)
else
    fval = ???
endif

end subroutine

解决方案

you can't. not easily. there are two things you can do, though:

• first, you can use function pointers. there's a simple example at http://www.macresearch.org/advanced_fortran_90_callbacks_with_the_transfer_function - the idea is that you can pass the name of a function defined elsewhere. that may be enough to solve your problem.

• you can call a library that parses the string and evaluates the expression. i don't know of anything in fortran, but your fortran compiler may support calling c routines. for gfortran (and maybe others), this looks like it would work - http://www.gnu.org/s/libmatheval/ (example fortran code at http://www.gnu.org/s/libmatheval/manual/libmatheval.html#Fortran-sample-program)

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