When examining some legacy Fortran code, I've found a subroutine declaration that is the following:
SUBROUTINE CLIP2G (fcut,TIME,NUMS,NUMG,CLIPG,CLIPGL,CLIPGR,
* MODE,PHZ)
What does the * signify in this context? Does the star * mean that the subroutine declaration spans two lines rather than one line?
This is line continuation mark. It marks that this line is a continuation of the previous one. It may be any Fortran recognized character, but it must be placed in column 6. More thorough discussion of line continuations in fixed and free Fotran format is here.
Related
I have a project written in VS2010 with Intel Visual Fortran. I have a dump subroutine to write a 2D matrix into file:
subroutine Dump2D(Name,Nx,Ny,Res)
implicit none
integer i,j,Nx,Ny
real(8) :: Res(Nx,Ny)
character(len=30) name,Filename
logical alive
write(filename,*) trim(Name),".dat"
Write(*,*) "Saving ",trim(Name)," Please wait..."
open (10,file=filename)
do i=1,Ny
Write(10,FMt="(D21.13\)") (Res(j,i),j=1,Nx)
Write(10,*)
end do
close(10)
Write(*,*) "Save ",trim(Name),"Complete!"
return
end subroutine Dump2D
It is ok to compile and run. But when I compile in emacs using gfortran it gives me the error:
I think it's because the gfortran doesn't recognize \ in a format for a write command. How do I fix this problem?
Write(10,FMt="(D21.13\)") (Res(j,i),j=1,Nx)
1
Error: Unexpected element '\' in format string at (1)
The edit descriptor \ relates to backslash editing. This is a non-standard extension provided by the Intel compiler (and perhaps others). It is not supported by gfortran.
Such backslash editing is intended to affect carriage control. Much as in this answer such an effect can be handled with the (standard) non-advancing output.1
As you simply want to output each column of a matrix to a record/line you needn't bother with this effort.2 Instead (as you'll see in many other questions):
do i=1,Ny
write(10,fmt="(*(D21.13))") Res(:,i)
end do
There are also other approaches which a more general search will find.
1 The Intel compiler treats \ and $ in the same way.
2 There are subtle aspects of \, but I'll assume you don't care about those.
Another approach (although francescalus answer is better in your case) would be to build a format string that contains the number of elements to include in your row. One way of doing this is to use the following to build the format string (which uses an explicit space character to separate elements within a line in the file):
WRITE(fmtString, '(A,I0,A)') '(', Nx, '(D21.13,:,1X))' *
Then use the format string variable in your WRITE statement as so:
do i=1,Ny
Write(10,FMt=fmtString) (Res(j,i),j=1,Nx)
end do
This approach can also be very useful if you want to use something other than spaces to separate elements (e.g. commas or semicolons).
*As that's a little difficult to read, I will provide an example. For Nx = 3, this would be equivalent to:
fmtString = '(3(D21.13,:,1X))'
Which is 2 numbers formatted using D21.13, each followed by a space, and a final number formatted using D21.13, but without a space after it (as the ":" stops at the final item).
The backslash is not valid in Fortran 77 FORMAT statements. Gfortran will not compile it, unless you fix the code. There is no flag that will change that AFAIK (-fbackslash should not help here).
If I understand the intention correctly (and I may be wrong), the backslash does the same as the dollar sign in some other compilers and prevents terminating a record (line). In that case the advance="no" put in the write statement should help. It is Fortran 90, but you should not avoid it just for that reason.
I have a project written in VS2010 with Intel Visual Fortran. I have a dump subroutine to write a 2D matrix into file:
subroutine Dump2D(Name,Nx,Ny,Res)
implicit none
integer i,j,Nx,Ny
real(8) :: Res(Nx,Ny)
character(len=30) name,Filename
logical alive
write(filename,*) trim(Name),".dat"
Write(*,*) "Saving ",trim(Name)," Please wait..."
open (10,file=filename)
do i=1,Ny
Write(10,FMt="(D21.13\)") (Res(j,i),j=1,Nx)
Write(10,*)
end do
close(10)
Write(*,*) "Save ",trim(Name),"Complete!"
return
end subroutine Dump2D
It is ok to compile and run. But when I compile in emacs using gfortran it gives me the error:
I think it's because the gfortran doesn't recognize \ in a format for a write command. How do I fix this problem?
Write(10,FMt="(D21.13\)") (Res(j,i),j=1,Nx)
1
Error: Unexpected element '\' in format string at (1)
The edit descriptor \ relates to backslash editing. This is a non-standard extension provided by the Intel compiler (and perhaps others). It is not supported by gfortran.
Such backslash editing is intended to affect carriage control. Much as in this answer such an effect can be handled with the (standard) non-advancing output.1
As you simply want to output each column of a matrix to a record/line you needn't bother with this effort.2 Instead (as you'll see in many other questions):
do i=1,Ny
write(10,fmt="(*(D21.13))") Res(:,i)
end do
There are also other approaches which a more general search will find.
1 The Intel compiler treats \ and $ in the same way.
2 There are subtle aspects of \, but I'll assume you don't care about those.
Another approach (although francescalus answer is better in your case) would be to build a format string that contains the number of elements to include in your row. One way of doing this is to use the following to build the format string (which uses an explicit space character to separate elements within a line in the file):
WRITE(fmtString, '(A,I0,A)') '(', Nx, '(D21.13,:,1X))' *
Then use the format string variable in your WRITE statement as so:
do i=1,Ny
Write(10,FMt=fmtString) (Res(j,i),j=1,Nx)
end do
This approach can also be very useful if you want to use something other than spaces to separate elements (e.g. commas or semicolons).
*As that's a little difficult to read, I will provide an example. For Nx = 3, this would be equivalent to:
fmtString = '(3(D21.13,:,1X))'
Which is 2 numbers formatted using D21.13, each followed by a space, and a final number formatted using D21.13, but without a space after it (as the ":" stops at the final item).
The backslash is not valid in Fortran 77 FORMAT statements. Gfortran will not compile it, unless you fix the code. There is no flag that will change that AFAIK (-fbackslash should not help here).
If I understand the intention correctly (and I may be wrong), the backslash does the same as the dollar sign in some other compilers and prevents terminating a record (line). In that case the advance="no" put in the write statement should help. It is Fortran 90, but you should not avoid it just for that reason.
I have a Fortran 77 code that shows a comment in the first column and written double precision in the same line. now my text editor (Notepad++) is showing that as a statement. I am confused if it is a statement or a comment.
* double precision Ct,Jt,PDt,AeA0t,Zt,Cq,Jq,PDq,AeA0q,Zq,
* &Kt,Kq,Eta,J,PD,AeA0
First, the text editor syntax highlighting is not something you can trust 100%. It is just there to help you, but it can be wrong and it can differ from an editor to an editor.
Second, if that code compiles, it must be a comment. Otherwise the ampersand & would cause an error. The ampersand can be used in the sixth column to continue the previous line, but it has to be the first character of the line.
It's a comment. If there's anything other than a whitespace in the first column of a line in a fixed-form fortran (That is Fortran up to F77), it's a comment.
These variables are not declared, but if the code doesn't have an implicit none, they would be implicitly declared, some as REAL, some as INTEGER.
I am converting some Fortran code to C and I don't understand what is going on here.
This code came from TOMS, Transactions on Mathematical Software, so I don't believe this is an errant line of code.
ZCOS and A have no other definitions in the file other than what I am showing here. Is this a Fortran technique for defining ZCOS as COS, and if so, what does it accomplish?
REAL ZCOS
ZCOS(A) = COS(A)
C(I) = ONE / (TWO * ZCOS ( C(I) * PI / DBLE(N+N) ))
This is a statement function, explained many times on SO. ZCOS is a real function and is defined in the first 2 lines.
The first line define the type of ZCOS.
The second line defines the function itself.
The third line could be an array access or another statement function. It cannot be decided without context.
Remark: Often, ZCOS is a specific functions for the COS generic, taking a double complex argument. It is a non-standard extension and your code does not use this intrinsic.
This is question about C99/C11 (may be C++ too) preprocessor and their standard-compliance.
Let's consider two source files:
/* I'm
* multiline
* comment
*/
and
/* I'm
* multiline
* comment
*/
i_am_a_token;
If we preprocess both files with gcc or clang (several version was tested), there will be a difference. In the first case preprocessor will not keep newlines from the multiline comment. And in the second case all newlines will be kept.
All mentioned standards says (somewhere inside "Translation phases"):
Each comment is replaced by one space character. New-line characters are retained.
Why there is the difference in handling multiline comments at the end of file? And is this behaviour standard-compliant?
The reason is simple - line numbers and error reporting. Since the compiler reports errors with line numbers, it is convenient so that line numbers in the pre-processed file correspond to line numbers in the original file. That's the reason the lines occupied by comment are preserved when they are followed by code, whereas they don't have to be preserved at the end of file.
As for the standards. The standards
C99: ISO/IEC 9899:1999
C11: ISO/IEC 9899:2011
specify the language, preprocessing macros etc., but they don't specify how the language should be processed. You can see it in the scope definition of C11:
ISO/IEC 9899:2011 does not specify
the mechanism by which C programs are transformed for use by a data-processing system;
which means that preprocessor output is pretty much internal issue, out of the scope of the standard.