Reading a character string of unknown length
I have been tasked with writing a Fortran 95 program that will read character input from a file, and then (to start with) simply spit it back out again. The tricky part is that
-
I'm using Fortran 90 to do this:
X = Len_Trim( Seq(I) ) ! length of individual sequence write(*,'(a<X>)') Seq(I)(1:X)You can simply declare Seq to be a large character string and then trim it as your write it out. I don't know how kosher this solution is but it certainly works for my purpose. I know that some compilers do not support "variable format expressions", but there are various workarounds to do the same thing almost as simply.
GNU Fortran variable expression workaround.
讨论(0) -
To progressively read a record in Fortran 95, use non-advancing input. For example:
CHARACTER(10) :: buffer INTEGER :: size READ (unit, "(A)", ADVANCE='NO', SIZE=size, EOR=10, END=20) bufferwill read up to 10 characters worth (the length of buffer) each time it is called. The file position will only advance to the next record (the next line) once the entire record has been read by a series of one or more non-advancing reads.
Barring an end of file condition, the
sizevariable will be defined with the actual number of characters read intobuffereach time the read statement is executed.The
EORandENDand specifiers are used to control execution flow (execution will jump to the appropriately labelled statement) when end of record or end of file conditions occur respectively. You can also use anIOSTATspecifier to detect these conditions, but the particular negative values to use for the two conditions are processor dependent.You can sum
sizewithin a particular record to work out the length of that particular record.Wrap such a non-advancing read in a loop that appropriately detects for end of file and end of record and you have the incremental reading part.
In Fortran 95, the length specification for a local character variable must be a specification expression - essentially an expression that can be safely evaluated prior to the first executable statement of the scope that contains the variable's declaration. Constants represent the simplest case, but a specification expression in a procedure can involve dummy arguments of that procedure, amongst other things.
Reading the entire record of arbitrary length in is then a multi stage process:
- Determine the length of the current record by using a series of incremental reads. These incremental reads for a particular record finish when the end of record condition occurs, at which time the file position will have moved to the next record.
Backspacethe file back to the record of interest.- Call a procedure, passing the length of the current record as a dummy argument. Inside that procedure have an character variable whose length is given by the dummy argument.
- Inside that called procedure, read the current record into that character variable using normal advancing input.
- Carry out further processing on that character variable!
Note that each record ends up being read twice - once to determine its length, the second to actually read the data into the correctly "lengthed" character variable.
Alternative approaches exist that use allocatable (or automatic) character arrays of length one. The overall strategy is the same. Look at the code of the Get procedures in the common ISO_VARYING_STRING implementation for an example.
Fortran 2003 introduces deferred length character variables, which can have their length specified by an arbitrary expression in an allocate statement or, for allocatable variables, by the length of the right hand side in an assignment statement. This (in conjunction with other "allocatable" enhancements) allows the progressive read that determines the record length to also build the character variable that holds the contents of the record. Your supervisor needs to bring his Fortran environment up to date.
讨论(0) -
Here's a function for Fortran 2003, which sets an allocatable string (InLine) of exactly the length of the input string (optionally trimmed), or returns .false. if end of file
function ReadLine(aunit, InLine, trimmed) result(OK) integer, intent(IN) :: aunit character(LEN=:), allocatable, optional :: InLine logical, intent(in), optional :: trimmed integer, parameter :: line_buf_len= 1024*4 character(LEN=line_buf_len) :: InS logical :: OK, set integer status, size OK = .false. set = .true. do read (aunit,'(a)',advance='NO',iostat=status, size=size) InS OK = .not. IS_IOSTAT_END(status) if (.not. OK) return if (present(InLine)) then if (set) then InLine = InS(1:size) set=.false. else InLine = InLine // InS(1:size) end if end if if (IS_IOSTAT_EOR(status)) exit end do if (present(trimmed) .and. present(InLine)) then if (trimmed) InLine = trim(adjustl(InLine)) end if end function ReadLineFor example to do something with all lines in a file with unit "aunit" do
character(LEN=:), allocatable :: InLine do while (ReadLine(aunit, InLine)) [.. something with InLine] end do讨论(0) -
I have used the following. Let me know if it is better or worse than yours.
!::::::::::::::::::::: SUBROUTINE OR FUNCTION ::::::::::::::::::::::::::::::::::::::: !__________________ SUBROUTINE lineread(filno,cargout,ios) __________________________ subroutine lineread(filno,cargout,ios) Use reallocate,ErrorMsg,SumStr1,ChCount ! this subroutine reads ! 1. following row in a file except a blank line or the line begins with a !#* ! 2. the part of the string until first !#*-sign is found or to end of string ! ! input Arguments: ! filno (integer) input file number ! ! output Arguments: ! cargout (character) output chArActer string, converted so that all unecessay spaces/tabs/control characters removed. implicit none integer,intent(in)::filno character*(*),intent(out)::cargout integer,intent(out)::ios integer::nlen=0,i,ip,ich,isp,nsp,size character*11,parameter::sep='=,;()[]{}*~' character::ch,temp*100 character,pointer::crad(:) nullify(crad) cargout=''; nlen=0; isp=0; nsp=0; ich=-1; ios=0 Do While(ios/=-1) !The eof() isn't standard Fortran. READ(filno,"(A)",ADVANCE='NO',SIZE=size,iostat=ios,ERR=9,END=9)ch ! start reading file ! read(filno,*,iostat=ios,err=9)ch; if(size>0.and.ios>=0)then ich=iachar(ch) else READ(filno,"(A)",ADVANCE='no',SIZE=size,iostat=ios,EOR=9); if(nlen>0)exit end if if(ich<=32)then ! tab(9) or space(32) character if(nlen>0)then if(isp==2)then isp=0; else isp=1; end if eend if; cycle; elseif(ich==33.or.ich==35.or.ich==38)then !if char is comment !# or continue sign & READ(filno,"(A)",ADVANCE='yes',SIZE=size,iostat=ios,EOR=9)ch; if(nlen>0.and.ich/=38)exit; else ip=scan(ch,sep); if(isp==1.and.ip==0)then; nlen=nlen+1; crad=>reallocate(crad,nlen); nsp=nsp+1; endif nlen=nlen+1; crad=>reallocate(crad,nlen); crad(nlen)=ch; isp=0; if(ip==1)isp=2; end if end do 9 if(size*ios>0)call ErrorMsg('Met error in reading file in [lineread]',-1) ! ios<0: Indicating an end-of-file or end-of-record condition occurred. if(nlen==0)return !write(6,'(a,l)')SumStr1(crad),eof(filno) !do i=1,nlen-1; write(6,'(a,$)')crad(i:i); end do; if(nlen>0)write(6,'(a)')crad(i:i) cargout=SumStr1(crad) nsp=nsp+1; i=ChCount(SumStr1(crad),' ',',')+1; if(len(cargout)<nlen)then call ErrorMsg(SumStr1(crad)// " is too long!",-1) !elseif(i/=nsp.and.nlen>=0)then ! call ErrorMsg(SumStr1(crad)// " has unrecognizable data number!",-1) end if end subroutine lineread讨论(0)
加载中...
- 热议问题