WANtaroHP (Fortran90 tips)

Outline of this page

Set the Value of π (pi)

• Webmaster is using the value of 'M_PI' which is included in the header file 'math.h' of C-language.

real(8),parameter::pi=3.14159265358979323846D0

Get the character strings from command line

• This function can be used in 'gfortran' system.
• Character strings are read from command line as array of characters.

call getarg(1,dummy)
call getarg(2,fnameR)
call getarg(3,fnameW)

Convert the character string to the figure

• Character string dummy is converted in figure negv.

read(dummy,*) negv

Convert the figure to character string

• In the following case, real number vec(i) is converted in character string dummy with comma (,) and the format '15e7'.
• By adding the comma, the character string can be used in the case of csv saving conveniently.

write(dummy,'(",",e15.7)') vec(i)

Create the sequence named file and write down the data

• In the do-statement, outputting is carried out using sequence named file created by the program.
• In this case, files are named such as '_inp_xyz_01.txt', '_inp_xyz_02.txt'.... and those are saved as a character string filename and used.

do n=1,ntout+1
    write (filename,'("_inp_xyz_",i2.2,".txt")') n
    open(13,file=filename,status='replace')
    do ne=1,NELT
        i=kakom(ne,1)
        write(13,*) x(i),y(i),tempe_s(i,n)
    end do
    close(13)
end do

Read the data from the file with unknown row numbers

• Existing file fnameR is opened with unit number = 11.
• Since number of the rows is unknown, existence of the row is checked using the variable io.
• In this case, the range of do-loop is from 1 to nn. Because the limit of array of character string str is specified. Limit number of character is 100 (mm=100) and limit number of row is 1000 (nn=1000).
• If EOF is detected, processing exits from do-loop.
• After that, number of row in file is saved in the variable nd.
• The meaning of the variable io is shown below.

zero ( 0 )	normal
negative value	EOF
positive value	error

• Please don't forget to declare the integer io.

    integer,parameter::nn=1000,mm=100
    character(len=mm)::str(1:nn)
    integer::i,io,nd
    character(len=50)::fnameR

    call getarg(1,fnameR)

    open(11,file=fnameR,status='old')
        do i=1,nn
            read(11,'(a)',iostat=io) str(i)
            if(io<0)exit
        end do
    close(11)
    nd=i-1

Write the data to the file

• New file fnameW with unit number=12 is created and data is written on it.
• When outputting the character string str(i), 'trim( )' and 'adjustl( )' are used because of unnecessity of front and trailing blanks.
• 'trim( )' is a procedure to remove trailing blank characters of a string, and 'adjustl( )' is the procedure to left adjust a string.
• If set unit number=6 as a expression write(6,'(a)'), the results are shown in the screen. It is convenient as a checking method during calculation processing.

open(12, file=fnameW, status='replace')
do i=1,nd
    write(12,'(a)') trim(adjustl(str(i)))
end do
close(12)

Specify the output format

• Specify output format using the string variable fmt3.
• Write the values on the string variable linebuf with the format specified by fmt3.
• It is necessary that string variable linebuf has enough length to store the characters.

fmt3="(i5,2(',',e15.7),3(',',e15.7))"
write(linebuf,FMT=fmt3) i,x(i),z(i),hvec(i),q0vec(i),hvec(i)

Delete all blanks (spaces) in character string

• This is a sample to delete all blanks in character string. In this case, subroutine 'del_spaces' is used.
• Subroutine 'del_spaces' is released in nag's website and webmaster is using it.
• The usage is very simple. String variable linebuf which includes some blanks is passed to subroutine 'del_spaces.'
• When outputting by write-statement, 'trim( )' is required.

call del_spaces(linebuf)
write (12,'(a)') trim(linebuf)

subroutine del_spaces(s)
    character (*), intent (inout) :: s
    character (len=len(s)) tmp
    integer i, j
    j = 1
    do i = 1, len(s)
       if (s(i:i)==' ') cycle
        tmp(j:j) = s(i:i)
        j = j + 1
    end do
    s = tmp(1:j-1)
end subroutine del_spaces

Convert the under-bar to blank in character string

• Even if the case of data reading from 'csv' file, Fortran compiler treats the blank as a data separator at the time of data reading. So, webmaster has made the subroutine 'rep_ub' which has the function of replacing under bars '_' to blankis ' ' in character string. (Ex: This_is_a_pen. ⇒ This is a pen.)
• The usage is very simple. String variable dummy which includes some under bars is passed to subroutine 'rep_ub.'
• If array of strings are used, following procedure is necessary.
• Make copy of array element str1(i) as a string variable dummy.
• Pass a string variable dummy to subroutine 'rep_ub'.
• Make copy of returned string variable dummy as an array element str1(i).
• Above steps are required in the use of subroutine 'del_spaces'

dummy=str1(i)
call rep_ub(dummy)
str1(i)=dummy

subroutine rep_ub(s)
    !Replacing underbar with space
    character (*), intent (inout) :: s
    integer i
    do i = 1, len(s)
        if (s(i:i)=='_') s(i:i)=' '
    end do
end subroutine rep_ub

Set the Value of π (pi) using module

module defpi
    implicit none
    real(8),parameter::pi=3.14159265358979323846D0
end module defpi

program f90_test
    use defpi
    implicit none
    .... .... ....
end program