11.3.3 Character Strings

Passing strings between C and Fortran routines is not recommended because there is no standard interface. However, note the following:

• All C strings are passed by reference.

• Fortran calls pass an additional argument for every argument with character type in the argument list. The extra argument gives the length of the string and is equivalent to a C long int passed by value. (This is implementation dependent.) The extra string-length arguments appear after the explicit arguments in the call.

A Fortran call with a character string argument is shown in the next example with its C equivalent:

CHARACTER*7 S
INTEGER B(3)
...
CALL CSTRNG( S, B(2) )
... 

char s[7];
int b[3];
...
cstrng_( s, &b[1], 7L );
... 

If the length of the string is not needed in the called routine, the extra arguments may be ignored. However, note that Fortran does not automatically terminate strings with the explicit null character that C expects. This must be added by the calling program.

The call for a character array looks identical to the call for a single character variable. The starting address of the array is passed, and the length that it uses is the length of a single element in the array.