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Old   March 14, 2007, 22:18
Default Fortran direct input help
  #1
Joe
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Hi,

This is a fortran code problem but I figure out the many fortran programmers might be able to help.

Suppose I have a simple code like this:

program test

integer :: i

print *, "input i"

read *, i

print *, i

end program test

Running the code will prompt me to enter "i", which will be printed.

Is there a way whereby I can input directly?

ie ./a.out 10

and "10" will be printed.

I was told by my school's computer staff that this is only possible in C, not fortran.

Is that true? Thank you.
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Old   March 15, 2007, 01:26
Default Re: Fortran direct input help
  #2
Ananda Himansu
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program test

integer :: i

read *, i

print *, i

end program test

Compile the above file, then run with

./a.out < 10

and "10" will be printed
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Old   March 15, 2007, 01:30
Default Re: Fortran direct input help
  #3
Markus Lummer
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Hi Joe,

look into the Fortran manual for functions/subroutines for the processing of command line arguments, e.g. function iargc() and subroutine getarg(...).

Regards, Markus

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Old   March 15, 2007, 01:34
Default oops my bad
  #4
Ananda Himansu
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on second thought, that will not work! Sorry, my mistake. you would need a file called "10" containing the input, in order for the code to work as I entered it. I guess the code the way you had it is the best that Fortran can do in general. There is no general mechanism in Fortran to parse command line arguments, though it is possible in Linux to enter

echo 10 | a.out

to achieve the effect you want
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Old   March 15, 2007, 04:20
Default Re: Fortran direct input help
  #5
Joe
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Thanks Ananada & Markus.

I've tried the subroutine getarg. I am able to get a character sting but I need the arguments to be in real nos.

How can I do that? Is there something like a character to real no. conversion subroutine? I've searched google but nothing meaningful appear.

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Old   March 15, 2007, 04:31
Default Re: Fortran direct input help
  #6
Markus Lummer
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Hi Joe,

in Fortran, you can read from a text string like from a file. In order to read the double precision variable number from the character string text, try e.g.

character text*(80) double precision number read(text,*) number

Regards, Markus
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Old   March 15, 2007, 04:32
Default Re: Fortran direct input help
  #7
Joe
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Hi,

Guess I was not looking hard enough. ;-)

For Intel compilers, the subroutine to convert character to real is dnum.

Thanks
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Old   March 15, 2007, 04:33
Default Re: Fortran direct input help
  #8
Markus Lummer
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Sorry, forgot the new lines.

character text*(80)

double precision number

read(text,*) number
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Old   March 15, 2007, 09:37
Default Re: Fortran direct input help
  #9
Joe
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Wow, I didn't know this is possible too. It's better than "dnum" cos any compiler can use it.

Thanks again
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