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variable string length function

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augh

augh

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Dec 21, 2008
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Here is another maybe-trivial--problem.

I cannot figure out how to write a character function that returns a variable-length string just like the intrinsic [tt]trim[/tt] does.

In the example below, the [tt]len[/tt] applied to [tt]trim[/tt] returns
the length of the trimmed string.

Code: 
character(len=100) :: qaz='qwerty'

print*,len(qaz)
print*,len(trim(qaz))

How can I write my own [tt]mytrim[/tt]?
How does fortran manage the length of strings?

 
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I don't know how to write trim() in Fortran but here is an example of a string functions which returns strings of variable length (I use gfortran)
Code: 
[COLOR=#a020f0]module[/color] my_functions
  [COLOR=#2e8b57][b]implicit[/b][/color] [COLOR=#2e8b57][b]none[/b][/color]
[COLOR=#a020f0]contains[/color]    
  [COLOR=#a020f0]function[/color] first_n(s, n)
    [COLOR=#0000ff]! returns first N characters of the string[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]):: s
    [COLOR=#2e8b57][b]integer[/b][/color]::n
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color]n):: first_n
    first_n [COLOR=#804040][b]=[/b][/color] s([COLOR=#ff00ff]1[/color]:n)
  [COLOR=#a020f0]end function[/color] first_n

  [COLOR=#a020f0]function[/color] substring(s, from_pos, to_pos)
    [COLOR=#0000ff]! returns substring from the given position to the given position[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]):: s
    [COLOR=#2e8b57][b]integer[/b][/color]:: from_pos, to_pos
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color]to_pos [COLOR=#804040][b]-[/b][/color] from_pos [COLOR=#804040][b]+[/b][/color] [COLOR=#ff00ff]1[/color]):: substring
    substring [COLOR=#804040][b]=[/b][/color] s(from_pos : to_pos)
  [COLOR=#a020f0]end function[/color] substring

[COLOR=#a020f0]end module[/color] my_functions

[COLOR=#a020f0]program[/color] strings
    [COLOR=#a020f0]use[/color] my_functions

    [COLOR=#2e8b57][b]implicit[/b][/color] [COLOR=#2e8b57][b]none[/b][/color]

    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]), [COLOR=#2e8b57][b]parameter[/b][/color] :: inputString [COLOR=#804040][b]=[/b][/color] [COLOR=#ff00ff]"Fortran is old programming language"[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color][COLOR=#ff00ff]7[/color])::outputString1
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color][COLOR=#ff00ff]2[/color])::outputString2    

    outputString1 [COLOR=#804040][b]=[/b][/color] first_n(inputString, [COLOR=#ff00ff]7[/color])
    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"output1 = '"[/color], outputString1,[COLOR=#ff00ff]"'"[/color]

    outputString2 [COLOR=#804040][b]=[/b][/color] substring(inputString, [COLOR=#ff00ff]9[/color], [COLOR=#ff00ff]10[/color])
    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"output2 = '"[/color], outputString2,[COLOR=#ff00ff]"'"[/color]

    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"output3 = '"[/color], substring(inputString, [COLOR=#ff00ff]12[/color], [COLOR=#ff00ff]14[/color]),[COLOR=#ff00ff]"'"[/color]
[COLOR=#a020f0]end program[/color] strings

Output:
Code: 
$ strings
 output1 = 'Fortran'
 output2 = 'is'
 output3 = 'old'

But note:
I need to declare the length of the output-string exactly before assigning the result of the string function in it.
If I try to define it variable e.g. instead of
Code: 
character(len=2)::outputString2
something like this
Code: 
character(len=*)::outputString2
I get an compile error:
Code: 
$ gfortran strings.f90 -o strings
strings.f90:30.35:

    character(len=*)::outputString2    
                                  1
Error: Entity with assumed character length at (1) must be a dummy argument or   PARAMETER
 
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I added the function my_trim(), which i created using intrinsic trim() :-)
Code: 
[COLOR=#a020f0]module[/color] my_functions
  [COLOR=#2e8b57][b]implicit[/b][/color] [COLOR=#2e8b57][b]none[/b][/color]
[COLOR=#a020f0]contains[/color]    
  [COLOR=#a020f0]function[/color] first_n(s, n)
    [COLOR=#0000ff]! returns first N characters of the string[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]):: s
    [COLOR=#2e8b57][b]integer[/b][/color]::n
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color]n):: first_n
    first_n [COLOR=#804040][b]=[/b][/color] s([COLOR=#ff00ff]1[/color]:n)
  [COLOR=#a020f0]end function[/color] first_n

  [COLOR=#a020f0]function[/color] substring(s, from_pos, to_pos)
    [COLOR=#0000ff]! returns substring from the given position to the given position[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]):: s
    [COLOR=#2e8b57][b]integer[/b][/color]:: from_pos, to_pos
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color]to_pos [COLOR=#804040][b]-[/b][/color] from_pos [COLOR=#804040][b]+[/b][/color] [COLOR=#ff00ff]1[/color]):: substring
    substring [COLOR=#804040][b]=[/b][/color] s(from_pos : to_pos)
  [COLOR=#a020f0]end function[/color] substring

  [COLOR=#a020f0]function[/color] my_trim(s)
    [COLOR=#0000ff]! returns substring from the given position to the given position[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]):: s
    [COLOR=#2e8b57][b]integer[/b][/color]:: n 
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#008080]len[/color]([COLOR=#008080]trim[/color](s))):: my_trim
    my_trim [COLOR=#804040][b]=[/b][/color] [COLOR=#008080]trim[/color](s)
  [COLOR=#a020f0]end function[/color] my_trim

[COLOR=#a020f0]end module[/color] my_functions

[COLOR=#a020f0]program[/color] strings
    [COLOR=#a020f0]use[/color] my_functions

    [COLOR=#2e8b57][b]implicit[/b][/color] [COLOR=#2e8b57][b]none[/b][/color]

    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]), [COLOR=#2e8b57][b]parameter[/b][/color] ::  inputString [COLOR=#804040][b]=[/b][/color] [COLOR=#ff00ff]"Fortran is old programming language"[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=*[/b][/color]), [COLOR=#2e8b57][b]parameter[/b][/color] ::  blah [COLOR=#804040][b]=[/b][/color] [COLOR=#ff00ff]" Blah Blah Blah                "[/color]
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color][COLOR=#ff00ff]7[/color])::outputString1
    [COLOR=#2e8b57][b]character[/b][/color]([COLOR=#2e8b57][b]len[/b][/color][COLOR=#804040][b]=[/b][/color][COLOR=#ff00ff]2[/color])::outputString2    

    outputString1 [COLOR=#804040][b]=[/b][/color] first_n(inputString, [COLOR=#ff00ff]7[/color])
    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"output1 = '"[/color], outputString1,[COLOR=#ff00ff]"'"[/color]

    outputString2 [COLOR=#804040][b]=[/b][/color] substring(inputString, [COLOR=#ff00ff]9[/color], [COLOR=#ff00ff]10[/color])
    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"output2 = '"[/color], outputString2,[COLOR=#ff00ff]"'"[/color]

    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"output3 = '"[/color], substring(inputString, [COLOR=#ff00ff]12[/color], [COLOR=#ff00ff]14[/color]),[COLOR=#ff00ff]"'"[/color]

    [COLOR=#804040][b]print[/b][/color] [COLOR=#804040][b]*[/b][/color], [COLOR=#ff00ff]"Trimmed '"[/color], blah, [COLOR=#ff00ff]"' = '"[/color], my_trim(blah),[COLOR=#ff00ff]"'"[/color]
[COLOR=#a020f0]end program[/color] strings

If I try it to compile with gforran I get an error on the last program line where I call this function
Code: 
$ gfortran strings.f90 -o strings
strings.f90: In function 'strings':
strings.f90:48: internal compiler error: Segmentation fault
Please submit a full bug report,
with preprocessed source if appropriate.
See <[URL unfurl="true"]http://gcc.gnu.org/bugs.html>[/URL] for instructions.

But if I try it to compile with g95 it compiles without error
Code: 
$ g95 strings.f90 -o strings
and works:
Code: 
$ strings
 output1 = 'Fortran'
 output2 = 'is'
 output3 = 'old'
 Trimmed ' Blah Blah Blah                ' = ' Blah Blah Blah'
 
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