I have an input text file that contains an integer record like:
1
which is read in Fortran code as:
read(iunit,'(i4)') int_var
which works fine with Gfortran, but the same code compiled with PGI Fortran Compiler expects a field 4 characters wide (the actual record is just 1 character) and throws an error. Now I know that the format specifies the width and this may or may not be correct behavior according to the Fortran standard, but my question is - is there a compiler option for PGI that would make it behave like Gfortran in this respect?
This 3rd party code I'm using has a lot (hundreds or thousands) of read statements like this and input data has a lot of records with "wrong" width so both modifying the code or the input data would require significant effort.
I don't think this is connected to blank. This read should not cause an error, unless you opened the file iunit with pad="no". Default is allways pad="yes", which causes the input record to be padded with blanks, if it is too short.
Are you sure, that you use correct input files, with correct line ends? There could be problems with text file that originate in Windows and in Unix the CR could be read in the input record. In this case using the unix2dos utility might help. You may try to read a character(4) string using the a4 edit descriptor to test for this.
Does PGI Fortran support the open keyword blank="null"? I think that this will change the read to the behavior that you want and minimize the modifications to the code. blank="null" versus blank="zero" doesn't seem to make a difference in gfortran 4.7.
Related
This question has been covered somewhat in previous SO questions. However, previous discussions seem somewhat incomplete.
Fortran has several I/O statements. There is READ(*,*) and WRITE(*,*), etc. The first asterisk (*) is the standard asterisk designating an input or output from the keyboard to/from the screen. My question is about the second asterisk:
The second asterisk designates the format of the I/O elements, the data TYPE which is being used. If this asterisk is left unchanged, the fortran complier uses the default format (whatever that may be, based on the compiler). Users must use a number of format descriptors to designate the data type, precision, and so forth.
(1) Are these format descriptors universal for all Fortran compilers and for all versions of Fortran?
(2) Where can I find the standard list of these format descriptors? For example, F8.3 means that the number should be printed using fixed point notation with field width 8 and 3 decimal places.
EDIT: A reference for edit descriptors can be found here: http://fortranwiki.org/fortran/show/Edit+descriptors
First, as a clarification, the 1st asterisk in the READ/WRITE statement has a slightly different meaning than you state. For write, it means write to the default file unit (in linux world generally standard out), for read it means read from the default file unit (in linux world generally standard in), either of which may not necessarily be connected to a terminal screen or a keyboard.
The 2nd asterisk means use list directed IO. For read statements this is generally useful because you don't need a specified format for your input. It breaks up the line into fields separated by space or comma (maybe a couple others that aren't commonly used), and reads each field in turn into the variable associated with that field in the argument list, ignoring unread fields, and continuing onto the next line if not enough fields were read in (unless a line termination character \ is explicitly included).
For writes, it means the compiler is allowed to determine what format to write the variables out (I believe with no separator). I believe it is allowed to do this at run time, so that you are all but guaranteed that the value it is trying to write will fit into the format specifier used, so you can be assured that you won't get ******* written out. The down side is you have to manually include a separator character in your argument list, or all your numbers will run together.
In general, using list directed read is more of a convenience to the user, so they don't have to fit their inputs into rigidly defined fields, and list directed writes are a convenience to the programmer, in case they're not sure what the output will look like.
When you have a data transfer statement like read(*,*) ... it's helpful to understand exactly what this means. read(*,*) is equivalent to the more verbose read(unit=*, fmt=*). This second asterisk, as you have it, makes this read statement (or corresponding write statement) list-directed.
List-directed input/output, as described elsewhere, is a convenience for the programmer. The Fortran standards specify lots of constraints that the compiler must follow, but this language has things like "reasonable values", so allowing output to vary by compiler, settings, and so on.
Again, as described elsewhere, fine user control over the output (or input) comes with giving a format specification. Instead of read(*,fmt=*), something like read(*,fmt=1014) or read(*,fmt=format_variable_or_literal). I take it your question is: what is this format specification?
I won't go into details of all of the possible edit descriptors, but I will say in response to (2): you can find the list of those edit descriptors in the Fortran standard (Clause 10 of Fortran 2008 goes into all the detail) or a good reference book.
To answer (1): no, edit descriptors are not universal. Even across Fortran standards. Of note are:
The introduction of I0 (and other minimal-width specifiers) for output in Fortran 95;
The removal of the H edit descriptor in Fortran 95;
The introduction of the DT edit descriptor in Fortran 2003.
I have noticed the results of list-directed output write(*,*) in Fortran is compiler dependent.
Indeed, with the code:
program one
real(8), dimension(5):: r1
do i=1,5
r1(i)=sqrt(i*10.0)
end do
write(*,*) (r1(i), i =1,5)
end program one
intel compiler ifort gives standard output broken by a newline:
3.16227769851685 4.47213602066040 5.47722530364990
6.32455539703369 7.07106781005859
while gfortran gives the equivalent one line result:
3.1622776601683795 4.4721359549995796 5.4772255750516612 6.3245553203367590 7.0710678118654755
I think that ifort is writing maximum 3 items per line (when floating real numbers).
Is there any way to make the ifort output be like gfrotran, i.e. avoid the newline?
Ideally, I would like to keep list-directed output (*,*) instructions, so I am looking for something like a compiler option or so, if any.
Since verson 14, intel fortran compiler has the wrap-margin function. By default, the record is wrapped after 80 characters. For disabling this restriction, you should specify:
on Linux: -no-wrap-margin
on WIndows: /wrap-margin-
See more on Intel Fortran's reference guide
No. List-directed (free-format) output provides convenience, but you give up control. Various aspects of the output are unspecified and allowed to be chosen to the compiler. If you want full control, you have to use formatted output.
Look into edit descriptors in your favorite Fortran book or online documentation. You can use fmt specifier in the write statement to specify edit descriptors. For example:
write(*,fmt='(5(F6.4,3X))') (r1(i), i =1,5)
should output something similar to:
3.1623 4.4721 5.4772 6.3246 7.0711
See https://software.intel.com/en-us/forums/topic/401555
Specify FORT_FMT_RECL or use
write (,"(G0,1X))"
This question has been covered somewhat in previous SO questions. However, previous discussions seem somewhat incomplete.
Fortran has several I/O statements. There is READ(*,*) and WRITE(*,*), etc. The first asterisk (*) is the standard asterisk designating an input or output from the keyboard to/from the screen. My question is about the second asterisk:
The second asterisk designates the format of the I/O elements, the data TYPE which is being used. If this asterisk is left unchanged, the fortran complier uses the default format (whatever that may be, based on the compiler). Users must use a number of format descriptors to designate the data type, precision, and so forth.
(1) Are these format descriptors universal for all Fortran compilers and for all versions of Fortran?
(2) Where can I find the standard list of these format descriptors? For example, F8.3 means that the number should be printed using fixed point notation with field width 8 and 3 decimal places.
EDIT: A reference for edit descriptors can be found here: http://fortranwiki.org/fortran/show/Edit+descriptors
First, as a clarification, the 1st asterisk in the READ/WRITE statement has a slightly different meaning than you state. For write, it means write to the default file unit (in linux world generally standard out), for read it means read from the default file unit (in linux world generally standard in), either of which may not necessarily be connected to a terminal screen or a keyboard.
The 2nd asterisk means use list directed IO. For read statements this is generally useful because you don't need a specified format for your input. It breaks up the line into fields separated by space or comma (maybe a couple others that aren't commonly used), and reads each field in turn into the variable associated with that field in the argument list, ignoring unread fields, and continuing onto the next line if not enough fields were read in (unless a line termination character \ is explicitly included).
For writes, it means the compiler is allowed to determine what format to write the variables out (I believe with no separator). I believe it is allowed to do this at run time, so that you are all but guaranteed that the value it is trying to write will fit into the format specifier used, so you can be assured that you won't get ******* written out. The down side is you have to manually include a separator character in your argument list, or all your numbers will run together.
In general, using list directed read is more of a convenience to the user, so they don't have to fit their inputs into rigidly defined fields, and list directed writes are a convenience to the programmer, in case they're not sure what the output will look like.
When you have a data transfer statement like read(*,*) ... it's helpful to understand exactly what this means. read(*,*) is equivalent to the more verbose read(unit=*, fmt=*). This second asterisk, as you have it, makes this read statement (or corresponding write statement) list-directed.
List-directed input/output, as described elsewhere, is a convenience for the programmer. The Fortran standards specify lots of constraints that the compiler must follow, but this language has things like "reasonable values", so allowing output to vary by compiler, settings, and so on.
Again, as described elsewhere, fine user control over the output (or input) comes with giving a format specification. Instead of read(*,fmt=*), something like read(*,fmt=1014) or read(*,fmt=format_variable_or_literal). I take it your question is: what is this format specification?
I won't go into details of all of the possible edit descriptors, but I will say in response to (2): you can find the list of those edit descriptors in the Fortran standard (Clause 10 of Fortran 2008 goes into all the detail) or a good reference book.
To answer (1): no, edit descriptors are not universal. Even across Fortran standards. Of note are:
The introduction of I0 (and other minimal-width specifiers) for output in Fortran 95;
The removal of the H edit descriptor in Fortran 95;
The introduction of the DT edit descriptor in Fortran 2003.
I'm currently in the process of upgrading an old program written in FORTRAN and I'm trying to get it to compile using gfortran. I can get it to build, however the program now chokes on the namelists that it is reading in.
An example of a namelist that came with the program is shown below. It cannot correctly read this file due to the space between the variable name and the parenthesis. Since these files are very large, is there anyway I can tell gfortran to expect an older namelist format?
&<NAME>
<VARNAME> (1) = 0,
<VARNAME> (2) = -1e-13,
<VARNAME> (3) = 0.2983
&End
If not, I can resort to doing a search/replace but I'd rather not mess with the data and just have the code successfully read it in.
Namelist is quite complicated, as you can tell from the fact that there are 92 namelist test cases in the gfortran testsuite.
gfortran has no option to do what you ask. You will probably have to remove the blanks by hand or by sed, like Vladimir F suggested.
I might add that blanks in the subobject designator (the varname(i) part) are explicitly forbidden in the F2003 standard 10.10.1.1:
"In the input record, each object name or subobject designator may be preceded and followed by one or more optional blanks but shall not contain embedded blanks."
so this is unlikely to be changed in a future version of gfortran.
My Fortran code needs to read a initialize data (about 24000 real numbers) from a file. Are there any ways to put the data in the code so that I can avoid accessing the filesystem?
I tried to use a module and put all the data into a variable initialization like this:
real(kind=8) :: a(24000)=(/&
& 1. ,&
& 2. ,&
...
&/)
but because of there are 24000 lines for the source file, I keep receiving compiling error "Too many continuation lines". Are there any solution to this?
You can use DATA statements for this.
The fact that you can "slice" up your array into sections (such as setting a[1..100] in one section, a[101..200] in the next and so on) means that you should be able to avoid the massive-statement-size problem you're experiencing.
For such a large amount of data I would use some script language (or even Fortran) to generate a chunk of simple Fortran code like
a(1) = ..
a(2) = ..
a(3) = ..
This code could be then copy-pasted or include-d into your source code.
One option may be to instruct your compiler to allow unlimited line lengths
and put the whole darn thing on one line.
gfortran -ffree-line-length-none
I've verified this works. I've got a 2Mb source file with just 3 lines
real(kind=8) :: a(24000)=(/ ......... /)
write(*,*)a(24000)
end
I wouldn't be surprised if some compiler has a practical line length limit though.
By the way gfortran does not like using a big data statement.
No error it just hangs (or takes a very long time )
//
Imagine that, my big data version actually compiled (and runs fine ) after 1.5 hours. Why data is handled by the compiler so vastly differently from an initialization assignment is a good question.
As the previous author stated you can use the data statement, but it can be time consuming to enter it into the code manually. Is there a reason that you are apprehensive about the use of a READ statement in a do loop to read in the file? If you can provide us with any input on the data file format we can better help you.
It might seem to be archaic, but you could use INCLUDE. You'd need to modify your data file to have the form you gave,
real(8), dimension(24000) :: a=(/1.0,2.0,...24000./)
and then include it in the main program as such:
program main
implicit none
include "my_data_file.for"
< ... >
end program main
You won't need to change your compilation command, your Fortran compiler will import the included file on its own--so long as the included file is in the same directory.