Using read(*,*) in Fortran doesn't seem to work if the string to be read from the user contains spaces.
Consider the following code:
character(Len = 1000) :: input = ' '
read(*,*) input
If the user enters the string "Hello, my name is John Doe", only "Hello," will be stored in input; everything after the space is disregarded. My assumption is that the compiler assumes that "Hello," is the first argument, and that "my" is the second, so to capture the other words, we'd have to use something like read(*,*) input1, input2, input3... etc. The problem with this approach is that we'd need to create large character arrays for each input, and need to know exactly how many words will be entered.
Is there any way around this? Some function that will actually read the whole sentence, spaces and all?
character(100) :: line
write(*,'("Enter some text: ",\)')
read(*,'(A)') line
write(*,'(A)') line
end
... will read a line of text of maximum length 100 (enough for most practical purposes) and write it out back to you. Modify to your liking.
Instead of read(*, *), try read(*, '(a)'). I'm no Fortran expert, but the second argument to read is the format specifier (equivalent to the second argument to sscanf in C). * there means list format, which you don't want. You can also say a14 if you want to read 14 characters as a string, for example.
Related
In Swift I can create a String variable such as this:
let s = "Hello\nMy name is Jack!"
And if I use s, the output will be:
Hello
My name is Jack!
(because the \n is a linefeed)
But what if I want to programmatically obtain the raw characters in the s variable? As in if I want to actually do something like:
let sRaw = s.raw
I made the .raw up, but something like this. So that the literal value of sRaw would be:
Hello\nMy name is Jack!
and it would literally print the string, complete with literal "\n"
Thank you!
The newline is the "raw character" contained in the string.
How exactly you formed the string (in this case from a string literal with an escape sequence in source code) is not retained (it is only available in the source code, but not preserved in the resulting program). It would look exactly the same if you read it from a file, a database, the concatenation of multiple literals, a multi-line literal, a numeric escape sequence, etc.
If you want to print newline as \n you have to convert it back (by doing text replacement) -- but again, you don't know if the string was really created from such a literal.
You can do this with escaped characters such as \n:
let secondaryString = "really"
let s = "Hello\nMy name is \(secondaryString) Jack!"
let find = Character("\n")
let r = String(s.characters.split(find).joinWithSeparator(["\\","n"]))
print(r) // -> "Hello\nMy name is really Jack!"
However, once the string s is generated the \(secondaryString) has already been interpolated to "really" and there is no trace of it other than the replaced word. I suppose if you already know the interpolated string you could search for it and replace it with "\\(secondaryString)" to get the result you want. Otherwise it's gone.
Is there a multiline string literal syntax in Matlab or is it necessary to concatenate multiple lines?
I found the verbatim package, but it only works in an m-file or function and not interactively within editor cells.
EDIT: I am particularly after readbility and ease of modifying the literal in the code (imagine it contains indented blocks of different levels) - it is easy to make multiline strings, but I am looking for the most convenient sytax for doing that.
So far I have
t = {...
'abc'...
'def'};
t = cellfun(#(x) [x sprintf('\n')],t,'Unif',false);
t = horzcat(t{:});
which gives size(t) = 1 8, but is obviously a bit of a mess.
EDIT 2: Basically verbatim does what I want except it doesn't work in Editor cells, but maybe my best bet is to update it so it does. I think it should be possible to get current open file and cursor position from the java interface to the Editor. The problem would be if there were multiple verbatim calls in the same cell how would you distinguish between them.
I'd go for:
multiline = sprintf([ ...
'Line 1\n'...
'Line 2\n'...
]);
Matlab is an oddball in that escape processing in strings is a function of the printf family of functions instead of the string literal syntax. And no multiline literals. Oh well.
I've ended up doing two things. First, make CR() and LF() functions that just return processed \r and \n respectively, so you can use them as pseudo-literals in your code. I prefer doing this way rather than sending entire strings through sprintf(), because there might be other backslashes in there you didn't want processed as escape sequences (e.g. if some of your strings came from function arguments or input read from elsewhere).
function out = CR()
out = char(13); % # sprintf('\r')
function out = LF()
out = char(10); % # sprintf('\n');
Second, make a join(glue, strs) function that works like Perl's join or the cellfun/horzcat code in your example, but without the final trailing separator.
function out = join(glue, strs)
strs = strs(:)';
strs(2,:) = {glue};
strs = strs(:)';
strs(end) = [];
out = cat(2, strs{:});
And then use it with cell literals like you do.
str = join(LF, {
'abc'
'defghi'
'jklm'
});
You don't need the "..." ellipses in cell literals like this; omitting them does a vertical vector construction, and it's fine if the rows have different lengths of char strings because they're each getting stuck inside a cell. That alone should save you some typing.
Bit of an old thread but I got this
multiline = join([
"Line 1"
"Line 2"
], newline)
I think if makes things pretty easy but obviously it depends on what one is looking for :)
My data looks like this
-3442.77 -16749.64 893.08 -3442.77 -16749.64 1487.35 -3231.45 -16622.36 902.29
.....
159*2539.87 10*0.00 162*2539.87 10*0.00
which means I start with either 7 or 8 reals per line and then (towards the end) have 159 values of 2539.87 followed by 10 values of 0 followed by 162 of 2539.87 etc. This seems to be a space-saving method as previous versions of this file format were regular 6 reals per line.
I am already reading the data into a string because of not knowing whether there are 7 or 8 numbers per line. I can therefore easily spot lines that contain *. But what then? I suppose I have to identify the location of each * and then identify the integer number before and real value after before assigning to an array. Am I missing anything?
Read the line. Split it into tokens delimited by whitespace(s). Replace the * in tokens that have it with space. Then read from the string one or two values, depending on wheather there was an asterisk or not. Sample code follows:
REAL, DIMENSION(big) :: data
CHARACTER(LEN=40) :: token
INTEGER :: iptr, count, idx
REAL :: val
iptr = 1
DO WHILE (there_are_tokens_left)
... ! Get the next token into "token"
idx = INDEX(token, "*")
IF (idx == 0) THEN
READ(token, *) val
count = 1
ELSE
! Replace "*" with space and read two values from the string
token(idx:idx) = " "
READ(token, *) count, val
END IF
data(iptr:iptr+count-1) = val ! Add "val" "count" times to the list of values
iptr = iptr + count
END DO
Here I have arbitrarily set the length of the token to be 40 characters. Adjust it according to what you expect to find in your input files.
BTW, for the sake of completeness, this method of compressing something by replacing repeating values with value/repetition-count pairs is called run-length encoding (RLE).
Your input data may have been written in a form suitable for list directed input (where the format specification in the READ statement is simply ''*''). List directed input supports the r*c form that you see, where r is a repeat count and c is the constant to be repeated.
If the total number of input items is known in advance (perhaps it is fixed for that program, perhaps it is defined by earlier entries in the file) then reading the file is as simple as:
REAL :: data(size_of_data)
READ (unit, *) data
For example, for the last line shown in your example on its own ''size_of_data'' would need to be 341, from 159+10+162+10.
With list directed input the data can span across multiple records (multiple lines) - you don't need to know how many items are on each line in advance - just how many appear in the next "block" of data.
List directed input has a few other "features" like this, which is why it is generally not a good idea to use it to parse "arbitrary" input that hasn't been written with it in mind - use an explicit format specification instead (which may require creating the format specification on the fly to match the width of the input field if that is not know ahead of time).
If you don't know (or cannot calculate) the number of items in advance of the READ statement then you will need to do the parsing of the line yourself.
I am reading from a file in Fortran which has an undetermined number of floating point values on each line (for now, there are about 17 values on a line). I would like to read the 'n'th value on each line to a given floating point variable. How should i go about doing this?
In C the way I wrote it was to read the entire line onto the string and then do something like the following:
for(int il = 0; il < l; il++)
{
for(int im = -il; im <= il; im++)
pch = strtok(NULL, "\t ");
}
for(int im = -l; im <= m; im++)
pch = strtok(NULL, "\t ");
dval = atof(pch);
Here I am continually reading a value and throwing it away (thus shortening the string) until I am ready to accept the value I am trying to read.
Is there any way I can do this in Fortran? Is there a better way to do this in Fortran? The problem with my Fortran code seems to be that read(tline, '(f10.15)') tline1 does not shorten tline (tline is my string holding the entire line and tline1 what i am trying to parse it into), thus I cannot use the same method as I did in my C routine.
Any help?
The issue is that Fortran is a record-based I/O system while C is stream-based.
If you have access to a Fortran 2003 compliant compiler (modern versions of gfortran should work), you can use the stream ACCESS specifier to do what you want.
An example can be found here.
Of course, if you were really inclined, you could just use your C function directly from Fortran. Interfacing the two languages is generally simple, typically only requiring a wrapper with a lowercase name and an appended underscore (depending on compiler and platform of course). Passing arrays or strings back and forth is not so trivial typically; but for this example that wouldn't be needed.
Once the data is in a character array, you can read it into another variable as you are doing with the ADVANCE=no signature, ie.
do i = 1, numberIWant
read(tline, '(F10.15)', ADVANCE="no") tline1
end do
where tline should contain your number at the end of the loop.
Because of the record-based I/O, a READ statement will typically throw out what is after the end of the record. But the ADVANCE=no tells it not to.
If you know exactly at what position the value you want starts, you can use the T edit descriptor to initiate the next read from that position.
Let's say, for instance, that the width of each field is 10 characters and you want to read the fifth value. The read statement will then look something like the following.
read(file_unit, '(t41, f10.5)') value1
P.s.: You can dynamically create a format string at runtime, with the correct number after the t, by using a character variable as format and use an internal file write to put in this number.
Let's say you want the value that starts at position n. It will then look something like this (I alternated between single and double quotes to try to make it more clear where each string starts and stops):
write(my_format, '(a, i0, a)') "(t", n, ', f10.5)'
read(file_unit, my_format) value1
I've a question about Fortran 77 and I've not been able to find a solution.
I'm trying to store an array of strings defined as the following:
character matname(255)*255
Which is an array of 255 strings of length 255.
Later I read the list of names from a file and I set the content of the array like this:
matname(matcount) = mname
EDIT: Actually mname value is hardcoded as mname = 'AIR' of type character*255, it is a parameter of a function matadd() which executes the previous line. But this is only for testing, in the future it will be read from a file.
Later on I want to print it with:
write(*,*) matname(matidx)
But it seems to print all the 255 characters, it prints the string I assigned and a lot of garbage.
So that is my question, how can I know the length of the string stored?
Should I have another array with all the lengths?
And how can I know the length of the string read?
Thanks.
You can use this function to get the length (without blank tail)
integer function strlen(st)
integer i
character st*(*)
i = len(st)
do while (st(i:i) .eq. ' ')
i = i - 1
enddo
strlen = i
return
end
Got from here: http://www.ibiblio.org/pub/languages/fortran/ch2-13.html
PS: When you say: matname(matidx) it gets the whole string(256) chars... so that is your string plus blanks or garbage
The function Timotei posted will give you the length of the string as long as the part of the string you are interested in only contains spaces, which, if you are assigning the values in the program should be true as FORTRAN is supposed to initialize the variables to be empty and for characters that means a space.
However, if you are reading in from a file you might pick up other control characters at the end of the lines (particularly carriage return and/or line feed characters, \r and/or \n depending on your OS). You should also toss those out in the function to get the correct string length. Otherwise you could get some funny print statements as those characters are printed as well.
Here is my version of the function that checks for alternate white space characters at the end besides spaces.
function strlen(st)
integer i,strlen
character st*(*)
i = len(st)
do while ((st(i:i).eq.' ').or.(st(i:i).eq.'\r').or.
+ (st(i:i).eq.'\n').or.(st(i:i).eq.'\t'))
i = i - 1
enddo
strlen = i
return
end
If there are other characters in the "garbage" section this still won't work completely.
Assuming that it does work for your data, however, you can then change your write statement to look like this:
write(*,*) matname(matidx)(1:strlen(matname(matidx)))
and it will print out just the actual string.
As to whether or not you should use another array to hold the lengths of the string, that is up to you. the strlen() function is O(n) whereas looking up the length in a table is O(1). If you find yourself computing the lengths of these static strings often, it may improve performance to compute the length once when they are read in, store them in an array and look them up if you need them. However, if you don't notice the slowdown, I wouldn't worry about it.
Depending on the compiler that you are using, you may be able to use the trim() intrinsic function to remove any leading/trailing spaces from a string, then process it as you normally would, i.e.
character(len=25) :: my_string
my_string = 'AIR'
write (*,*) ':', trim(my_string), ':'
should print :AIR:.
Edit:
Better yet, it looks like there is a len_trim() function that returns the length of a string after it has been trimmed.
intel and Compaq Visual Fortran have the intrinsic function LEN_TRIM(STRING) which returns the length without trailing blanks or spaces.
If you want to suppress leading blanks or spaces, use "Adjust Left" i.e. ADJUSTF(STRING)
In these FORTRANs I also note a useful feature: If you pass a string in to a function or subroutine as an argument, and inside the subroutine it is declared as CHARACTER*(*), then
using the LEN(STRING) function in the subroutine retruns the actual string length passed in, and not the length of the string as declared in the calling program.
Example:
CHARACTER*1000 STRING
.
.
CALL SUBNAM(STRING(1:72)
SUBROUTINE SYBNAM(STRING)
CHARACTER*(*) STRING
LEN(STRING) will be 72, not 1000