Fortran Programming Language :: returning a string from a C function


	returning a string from a C function Hi, Is it possible to return a string from C? I'm trying the below to no avail C Fortran CHARACTER(len=30) fstr INTERFACE FUNCTION foo() CHARACTER(30) :: foo END FUNCTION END INTERFACE fstr=foo () print 10, fstr 10 format('string returned = [',a30,']') and the C function char * foo_() { char retstr; retstr=malloc(30); strcpy(retstr,"String returned from C"); return retstr; } any suggestions? Thanks igl@gmail.com wrote: > Is it possible to return a string from C? > I'm trying the below to no avail > C Fortran > CHARACTER(len=30) fstr > INTERFACE > FUNCTION foo() > CHARACTER(30) :: foo > END FUNCTION > END INTERFACE > fstr=foo () > print 10, fstr > 10 format('string returned = [',a30,']') It isn't easy to do in Fortran. Note that your C function doesn't return a string, in the Fortran sense, but a pointer. In most cases it is fairly obvious how to write a Fortran callable C routine, but this isn't one of those cases. I believe Fortran functions returning a known (at compile time) length add it as an extra argument before or after the other arguments, but you should find out specifically for your implementation. Much easier to write it as a subroutine ( (void) function) with the string as an argument. Otherwise, wait until Fortran 2003 compilers are available. > char foo_() { > char retstr; > retstr=malloc(30); > strcpy(retstr,"String returned from C"); > return retstr; > } If you do this, how do you expect to free() the string? Note that almost no C code does this because of the need to free() the return string. Some C library routines return a pointer to a static string. -- glen In John Reid's doccument about the new features of fortran 2003, he states tha when interacting between C and Fortran, the "len" property of a character must always be 1. CHARACTER(LEN=1), DIMENSION(30) :: fstr might work better. As far as C is concerned a string of characters is just an array of individual char elements. Fortran's implimentation is slightly different since it has the len property. I recomend googlng John Reid's text for more information. - Hide quoted text - igl@gmail.com wrote: > Hi, > Is it possible to return a string from C? > I'm trying the below to no avail > C Fortran > CHARACTER(len=30) fstr > INTERFACE > FUNCTION foo() > CHARACTER(30) :: foo > END FUNCTION > END INTERFACE > fstr=foo () > print 10, fstr > 10 format('string returned = [',a30,']') > and the C function > char foo_() { > char retstr; > retstr=malloc(30); > strcpy(retstr,"String returned from C"); > return retstr; > } > any suggestions? > Thanks Hello, in the corrigenda to Mike Metcalf's et al., Fortran 95/2003, this has been changed to be allowed. So you can indeed associate an actual character(len=10,kind=c_char) stuff with a char ; the Fortran-provided interface then requires character(kind=c_char), dimension() :: dummy_stuff Regards aerospace1@hotmail.com schrieb: - Hide quoted text - > In John Reid's doccument about the new features of fortran 2003, he > states tha when interacting between C and Fortran, the "len" property > of a character must always be 1. > CHARACTER(LEN=1), DIMENSION(30) :: fstr > might work better. > As far as C is concerned a string of characters is just an array of > individual char elements. Fortran's implimentation is slightly > different since it has the len property. > I recomend googlng John Reid's text for more information. > igl@gmail.com wrote: >> Hi, >> Is it possible to return a string from C? >> I'm trying the below to no avail >> C Fortran >> CHARACTER(len=30) fstr >> INTERFACE >> FUNCTION foo() >> CHARACTER(30) :: foo >> END FUNCTION >> END INTERFACE >> fstr=foo () >> print 10, fstr >> 10 format('string returned = [',a30,']') >> and the C function >> char foo_() { >> char retstr; >> retstr=malloc(30); >> strcpy(retstr,"String returned from C"); >> return retstr; >> } >> any suggestions? >> Thanks On May 16, 4:39 pm, igl@gmail.com wrote: - Hide quoted text - > Hi, > Is it possible to return a string from C? > I'm trying the below to no avail > C Fortran > CHARACTER(len=30) fstr > INTERFACE > FUNCTION foo() > CHARACTER(30) :: foo > END FUNCTION > END INTERFACE > fstr=foo () > print 10, fstr > 10 format('string returned = [',a30,']') > and the C function > char foo_() { > char *retstr; > retstr=malloc(30); > strcpy(retstr,"String returned from C"); > return retstr; > } > any suggestions? > Thanks one trick I have seen to work is to make the C string a structure - with two components - (a pointer to the beginning of )the string and the length. This imitates Fortran's fixed length strings and you should be able to pass strings back and forth without problems.