From Newsgroup: comp.lang.fortran

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile
time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

Thanks,
Lynn

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From Newsgroup: comp.lang.fortran

Lynn McGuire <lynnmcguire5@gmail.com> schrieb:

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

A full, self-contained example would be helpful for somebody trying to
help (especially since you say "link", which seems weird).

But take a look at

https://gcc.gnu.org/onlinedocs/gfortran/Naming-and-argument-passing-conventions.html

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

It is generally a good idea to use ISO C binding in new code, it
is what it was introduced for.

But you might also find

https://gcc.gnu.org/onlinedocs/gfortran/Interoperability-Options.html

of interest.
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From Newsgroup: comp.lang.fortran

On Thu, 02 Jan 2025 02:27:54 -0600, Lynn McGuire wrote:

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

As Thomas as indicated, ISO C binding was introduced into the
Fortran standard to address your needs. But, if you want to
go old school with gcc/gfortran, then

% cat aa.c
#include <string.h>

void
string_(char *s, int *slen)
{
strncpy(s, "abc", *slen);
}

% cat bb.f90
program foo
external :: string
character(len=10) str
call string(str, len(str))
print *, '>>' // str //'<<'
end program foo

% ~/work/bin/gcc -c aa.c
% gfcx -o z bb.f90 aa.o
% ./z

abc<<

--
steve

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From Newsgroup: comp.lang.fortran

On 1/2/2025 4:06 AM, Thomas Koenig wrote:

Lynn McGuire <lynnmcguire5@gmail.com> schrieb:

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

A full, self-contained example would be helpful for somebody trying to
help (especially since you say "link", which seems weird).

But take a look at

https://gcc.gnu.org/onlinedocs/gfortran/Naming-and-argument-passing-conventions.html

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile
time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

It is generally a good idea to use ISO C binding in new code, it
is what it was introduced for.

But you might also find

https://gcc.gnu.org/onlinedocs/gfortran/Interoperability-Options.html

of interest.

Thanks ! When I was writing the reply to you, I figured out the
problem. I forgot to put 'extern "C"' in front of the function
declaration for my fortran code. That fixed my link.

It is the little things that get you.

Thanks,
Lynn

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From Newsgroup: comp.lang.fortran

On 1/2/2025 12:40 PM, Steven G. Kargl wrote:

On Thu, 02 Jan 2025 02:27:54 -0600, Lynn McGuire wrote:

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile
time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

As Thomas as indicated, ISO C binding was introduced into the
Fortran standard to address your needs. But, if you want to
go old school with gcc/gfortran, then

% cat aa.c
#include <string.h>

void
string_(char *s, int *slen)
{
strncpy(s, "abc", *slen);
}

% cat bb.f90
program foo
external :: string
character(len=10) str
call string(str, len(str))
print *, '>>' // str //'<<'
end program foo

% ~/work/bin/gcc -c aa.c
% gfcx -o z bb.f90 aa.o
% ./z
>>abc<<

Isn't the character string length variable "slen" a value parameter and
size_t type ?

Lynn

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From Newsgroup: comp.lang.fortran

On Thu, 02 Jan 2025 16:38:10 -0600, Lynn McGuire wrote:

On 1/2/2025 12:40 PM, Steven G. Kargl wrote:

On Thu, 02 Jan 2025 02:27:54 -0600, Lynn McGuire wrote:

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile
time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

As Thomas as indicated, ISO C binding was introduced into the
Fortran standard to address your needs. But, if you want to
go old school with gcc/gfortran, then

% cat aa.c
#include <string.h>

void
string_(char *s, int *slen)
{
strncpy(s, "abc", *slen);
}

% cat bb.f90
program foo
external :: string
character(len=10) str
call string(str, len(str))
print *, '>>' // str //'<<'
end program foo

% ~/work/bin/gcc -c aa.c
% gfcx -o z bb.f90 aa.o
% ./z
>>abc<<

Isn't the character string length variable "slen" a value parameter and size_t type ?

'int *' is a pointer to an int. size_t may or may not be an int.

If one refuses to use the facilities of the Fortran standard,
namely ISO C binding, then one needs to experiment to determine
the type(s) and calling convention.
--
steve

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From Newsgroup: comp.lang.fortran

On Thu, 2 Jan 2025 02:27:54 -0600, Lynn McGuire wrote:

How do you send a fortran character string from GCC to GFortran ?

Seems like trying to call Fortran routines from C is not quite straightforward. Looking at the (draft?) Fortran 2023 spec, page 514 says:

In a reference from C to a Fortran procedure with an interoperable
interface, a C actual argument shall be the address of a C
descriptor for the intended effective argument if the
corresponding dummy argument interoperates with a C formal
parameter that is a pointer to CFI_cdesc_t.

The following section (page 516 onwards) defines these “C descriptors”. Or alternatively (back to page 514), you might need to declare your Fortran routine with the “BIND(C)” attribute.
--- Synchronet 3.20a-Linux NewsLink 1.114

From Newsgroup: comp.lang.fortran

On 2025-01-02 23:38, Lynn McGuire wrote:

Isn't the character string length variable "slen" a value parameter and size_t
type ?

Depends: gfortran 8 and subsequent versions use size_t, older versions and other
compilers use int AFAIK.

I guess, handling strings beyond 2GB is not a particular strength of Fortran anyway, so I don't know why that change was made.

Thomas

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From Newsgroup: comp.lang.fortran

Thomas Jahns <jahns@idontlikespam.dkrz.de> schrieb:

On 2025-01-02 23:38, Lynn McGuire wrote:

Isn't the character string length variable "slen" a value parameter and size_t
type ?

Depends: gfortran 8 and subsequent versions use size_t, older versions and other
compilers use int AFAIK.

I guess, handling strings beyond 2GB is not a particular strength of Fortran anyway, so I don't know why that change was made.

There should be as few artificial limitations in a compiler as possible.
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From Newsgroup: comp.lang.fortran

On 1/2/2025 4:06 AM, Thomas Koenig wrote:

Lynn McGuire <lynnmcguire5@gmail.com> schrieb:

How do you send a fortran character string from GCC to GFortran ?

I cannot get this to link. I can do the reverse, send a fortran
character string from Gfortran to GCC.

A full, self-contained example would be helpful for somebody trying to
help (especially since you say "link", which seems weird).

But take a look at

https://gcc.gnu.org/onlinedocs/gfortran/Naming-and-argument-passing-conventions.html

I do have the additional complication that I do not know the length of
the fortran character string being sent from GCC to Gfortran at compile
time, only run time. So that is a character*(*) string.

I am not using the ISO C binding.

It is generally a good idea to use ISO C binding in new code, it
is what it was introduced for.

But you might also find

https://gcc.gnu.org/onlinedocs/gfortran/Interoperability-Options.html

of interest.

BTW, I have thousands of calls from my Fortran code to my C code.
Adding all of the ISO C binding syntax will take a lot of time. And
breakage of what was working code using the Watcom Fortran and C compilers.

Lynn

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