Reading the rest of the line depending on the first character
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From: ivan martin on 27 Apr 2010 08:12 Good day everyone, please, I plead for your help. In fortran, what would be a practical way to read a line that can look like A 1. 2. 3. (numbers are made up, they do not increase like this) Z A 1. 2. 3. so, I wish to read a char and three numbers following it if the char is an "A", but read the char and quit reading at that point, if the char is a "Z". (Z marks the last line with numbers in my input file; other chars mark properties of points; so behind Z there will never be numbers). If I read it simply like read(unit=..., *)char,num1,num2,num3 then program will report an error if he does not encounter the numbers after Z. I would be thankful for any help you can give. Ivan
From: Bruce Bowler on 27 Apr 2010 08:55 On Tue, 27 Apr 2010 14:12:27 +0200, ivan martin set fingers to keyboard and typed: > Good day everyone, > please, I plead for your help. > > In fortran, what would be a practical way to read a line that can look > like > > A 1. 2. 3. (numbers are made up, they do not increase like this) Z > A 1. 2. 3. > > so, I wish to read a char and three numbers following it if the char is > an "A", but read the char and quit reading at that point, if the char is > a "Z". > > (Z marks the last line with numbers in my input file; other chars mark > properties of points; so behind Z there will never be numbers). > > If I read it simply like > read(unit=..., *)char,num1,num2,num3 > > then program will report an error if he does not encounter the numbers > after Z. > > I would be thankful for any help you can give. Ivan Pseudo code character(len="long enough"):: line read (5,*) line if (line(1:1) /= "Z") then read (line(2:end),*) num1,num2,num3 more processing endif -- +-------------------+---------------------------------------------------+ Bruce Bowler | One nice thing about egotists: They don't talk 1.207.633.9610 | about other people. bbowler(a)bigelow.org | - Lucille S. Harper +-------------------+---------------------------------------------------+
From: Jim Xia on 27 Apr 2010 10:52 On Apr 27, 8:55 am, Bruce Bowler <bbow...(a)bigelow.org> wrote: > On Tue, 27 Apr 2010 14:12:27 +0200, ivan martin set fingers to keyboard > and typed: > > > > > > > Good day everyone, > > please, I plead for your help. > > > In fortran, what would be a practical way to read a line that can look > > like > > > A 1. 2. 3. (numbers are made up, they do not increase like this) Z > > A 1. 2. 3. > > > so, I wish to read a char and three numbers following it if the char is > > an "A", but read the char and quit reading at that point, if the char is > > a "Z". > > > (Z marks the last line with numbers in my input file; other chars mark > > properties of points; so behind Z there will never be numbers). > > > If I read it simply like > > read(unit=..., *)char,num1,num2,num3 > > > then program will report an error if he does not encounter the numbers > > after Z. > > > I would be thankful for any help you can give. Ivan > > Pseudo code > > character(len="long enough"):: line > read (5,*) line > if (line(1:1) /= "Z") then > read (line(2:end),*) num1,num2,num3 > more processing > endif "read (5,*) line" wouldn't work as the input data look like "A 1. 2. 3.". Only "A" will be read in. What you want is "read (5, '(a)') line" Then the issue is leading character may be blank if the input has leading blanks. You have to use intrinsics like ADJUSTL() to remove the leading blanks. I'd suggest to use iostat= specifier to handle the error. It'll result in more robust code. However the flip side of the approach will be the dependencies on specific iostat values returned by different compilers. So choose the one you feel comfortable. Cheers, Jim
From: Dan Nagle on 27 Apr 2010 14:21 Hello, On 2010-04-27 10:52:36 -0400, Jim Xia <jimxia(a)hotmail.com> said: > "read (5,*) line" wouldn't work as the input data look like "A 1. 2. > 3.". Only "A" will be read in. What you want is > "read (5, '(a)') line" I think there should be an advance= 'no' or a backspace( 5) in there somewhere. backspacing may be problematic if 5 is stdin. <snip> > I'd suggest to use iostat= specifier to handle the error. It'll > result in more robust code. However the flip side of the approach > will be the dependencies on specific iostat values returned by > different compilers. So choose the one you feel comfortable. Well, if he's sure that the only end encountered will be end-of-line (and not end-of-file), he could test for only iostat > 0 But iostat is a good idea IAC. And the constants in iso_fortran_env may help. -- Cheers! Dan Nagle
From: Richard Maine on 27 Apr 2010 17:49
Dan Nagle <dannagle(a)verizon.net> wrote: > On 2010-04-27 10:52:36 -0400, Jim Xia <jimxia(a)hotmail.com> said: > > > "read (5,*) line" wouldn't work as the input data look like "A 1. 2. > > 3.". Only "A" will be read in. What you want is > > "read (5, '(a)') line" > > I think there should be an advance= 'no' or a backspace( 5) > in there somewhere. Those are alternative approaches. While they can also work ok in some cases, you don't need them *ALSO*; you could use them instead. The basic approaches commonly seen are 1. Read the whole line into a character buffer and parse the buffer (possibly with the help of internal reads). 2. Use non-advancing I/O (or a nonstandard variant such as the $ or \ edit descriptors). 3. Use backspace 4. (sort of - I almost forgot about this one until others mentioned simillar things) Assume that any error must be the one you might be expecting. That's pretty full of problems, though. I disrecommend it. Bruce (and Jim's correction) were mentioning approach 1. Approach 2 can also work. Depends on details while is better. Sometimes it is pretty much a coin toss or matter of personal taste. I usually recommend against the backspace approach because it can have many problems, including > backspacing may be problematic if 5 is stdin. > Well, if he's sure that the only end encountered > will be end-of-line (and not end-of-file), he could test > for only iostat > 0 Note that you won't ever get an "end-of-line" (more properly end-of-record) at all from any of the codes shown. That condition applies *ONLY* to non-advancing I/O. If you find a compiler that returns an end-of-line condition for advancing I/O, file a bug report. Well, that's the case through f2003 at least. I haven't checked the f2008 FDIS on the matter. I hope it is still the case there because otherwise it would be an incompatible change, though one of a kind that I've occasionally seen the committee overlook. Yes, it would be an incompatible change - not just a "new feature" to allow end-of-record for advancing I/O. That's because f77/f90/f95/f2003 code is allowed to assume that a negative iostat from an advancing read indicates end-of-file. It is completely standard conforming for a program to assume that. Thus changing it would be incompatible with existing standard conforming programs. (I elaborate so much because I have in the past had to explain simillar incompatibilities to multiple people on the committee. In particular, it came up when some people proposed to have f2003 allow multiple iostat values to indicate eof. Apparently one vendor already had such multiple values, not realizing that the standard prohibitted it. I objected to changing the standard to accomodate an error made by one vendor at the expense of invalidating existing standard-conforming codes.) -- Richard Maine | Good judgment comes from experience; email: last name at domain . net | experience comes from bad judgment. domain: summertriangle | -- Mark Twain |