Computational Astrophysics AS 3013 Lecture 6:

Transcription

1 Computational Astrophysics AS 3013 Lecture 6: 1) formated input/output 2) file input/output 3) safety checks

2 FORTRAN 90: formatted input/output list-directed (or default) format READ *, variable list PRINT *, expression list this is the method we have used so far I/O uses default devices (keyboard and screen) the * means use list-directed I/O, i.e. a suitable input/output format very practical for initial testing and quick messages ( don't care - format ) however, integer :: i real :: a(3) character(len=3) :: answer logical :: quit read *, i,a,answer,quit print *, your answer was:, & i,a,answer,quit result and program behaviour(!) may be compiler-dependent (what is suitable?) programmer has no control over form of numerical output, e.g. number of significant digits, and layout AS3013: F90 lecture 6 2

3 formatted input/output READ '(format list)', variable list PRINT '(format list)', expression list gives you full control over what happens makes the output more readable and comparable formatted read can be dangerous, if the input is not exactly as foreseen formatted print can be dangerous, if values are unexpected a few examples print '( ###,A7, ### )', Hallo print '( ###,A4, ### )', Hallo print '(F5.3)', print '(I3.2)', 2 print '(I4)', print '(1pE11.4E3)', 2.0/3.0 print '(2("#",F8.4,"#"))', (/0.1,1000.0/) / 3.0 ### Hallo### ###Hall### **** E-001 # ## # AS3013: F90 lecture 6 3

4 A-format Aw meant for text and characters w=width w>len => insert leading spaces (right justified) w<len => truncate text X-format Nx inserts N spaces character constants text inserts exactly the text between the... repetitions print '( ###,A7, ### )', Hallo print '( ###,A4, ### )', Hallo print '( ###,3x, ### )' ### Hallo### ###Hall### ### ### n(format list) print '( #,3(A1,1x), # )', A, B, C #A B C # - inserts format list n times AS3013: F90 lecture 6 4

5 I-format Iw or Iw.d meant for INTEGER expressions w=width d=number of digits (fill in leading zeros) don't forget the minus sign (!) some examples print '( ###,I3, ### )', 12 print '( ###,I3.3, ### )', 12 print '( ###,I3, ### )',-123 ### 12### ###012### ###***### AS3013: F90 lecture 6 5

6 F-format Fw.d meant for REAL expressions w=width d=number of digits after the comma last digit will be rounded don't forget to count the dot and the minus sign (!) suitable for numbers of the order of 1 not suitable for very small and very large numbers (!) some examples print '( ###,F6.2, ### )', print '( ###,F6.2, ### )', 1.0 print '( ###,F6.2, ### )', print '( ###,F6.2, ### )', 1 print '( ###,F6.2, ### )', 1.E-4 ###-12.35### ### 1.00### ###******### ### 0.00### ### 0.00### AS3013: F90 lecture 6 6

7 E-format Ew.d or Ew.dEn or 1pEw.dEn meant for REAL expressions w=width d=number of digits after the comma n=number of exponent digits 1p means to force an output with a leading digit <> 0 don't forget to count. E + - suitable for any real numbers some examples print '( ###,E11.4, ### )', print '( ###,E11.4E1, ### )', print '( ###,1pE11.4, ### )', print '( ###,E11.5, ### )', ### E+02### ### E+2### ### E+02### ###***********### AS3013: F90 lecture 6 7

8 FORTRAN 90: File Input/Output open and close files on harddisc open([unit=]u,file=name,...) close([unit=]u) u is an integer, the channel number name is a character constant or character variable specify the way you want to use the file create new output file with status = 'new' read existing file with status = 'old' create or overwrite output file with status = 'replace' add new output lines with position = 'append' check whether action was successful iostat = ok (ok must be defined as integer, will be ==0 for success) create or read unformatted files form = 'unformatted' ( direct access, kind of compressed, faster, not human readable) AS3013: F90 lecture 6 8

9 how to write to / read from files? write(u,'(format list)',...) expression list read (u,'(format list)',...) variable list use * (instead of u) to read from keyboard / write to screen use * (instead of format list) to use don't-care-format check success iostat=ok avoid carriage return with advance= no one example integer :: ok real :: x character(len=80) 5 :: name name= test.dat open(1,file=name,status='replace',iostat=ok) print '( file,a8, opened ok=,i3)', name,ok write(1,*) close(1) open(1,file=name,status='old',iostat=ok) print '( same file re-opened ok=,i3)', ok read(1,*) x close(1) print '( value read x=,f6.2)', x file test.dat opened ok= 0 same file re-opened ok= 0 value read x= 1.23 AS3013: F90 lecture 6 9

10 FORTRAN 90: safty checks how to check your input? integer :: IOcheck real :: x write(*, "(A)", ADVANCE="NO") "Enter a real number: " do read(*,*,iostat=iocheck) x if (IOcheck == 0) then exit! Leave loop when input form correct else print *, "sorry, I cannot interpret this input as REAL" write(*, "(A)", ADVANCE="NO") "Enter a REAL number, please: " endif enddo print '( value read x=,f6.2)' x Enter a real number: hallo sorry, I cannot interpret this input as REAL Enter a REAL number, please: 12,345 value read x= AS3013: F90 lecture 6 10

11 how to check for existing files? inquire(file=name, exist=ex) ex is a logical variable, needs to be declared how to append data to a file, savely? logical :: ex integer :: ok,unit real :: MyResult, HEAVY_COMPUTATION character(len=80) :: name MyResult = HEAVY_COMPUTATION(42) name = MyDataBase.dat unit = 1 inquire(file=name, exist=ex) if (ex) then open(unit,file=name,position='append',iostat=ok) else open(unit,file=name,status='new',iostat=ok) endif if (ok/=0) then print *, something went wrong, I could not open file,name stop endif write(unit,*) MyResult close(unit) AS3013: F90 lecture 6 11