XL Fortran Enterprise Edition for AIX : User's Guide - IBM

Common blocks that are declared THREADPRIVATE can be accessed using a C
global variable that is declared as THREADPRIVATE, using C for AIX 4.5 or later.
Passing Character Types between Languages
One difficult aspect of interlanguage calls is passing character strings between
languages. The difficulty is due to the following underlying differences in the way
that different languages represent such entities:
v
v
The only character type in Fortran is CHARACTER, which is stored as a set of
contiguous bytes, one character per byte. The length is not stored as part of the
entity. Instead, it is passed by value as an extra argument at the end of the
declared argument list when the entity is passed as an argument.
Character strings in C are stored as arrays of the type char. A null character
indicates the end of the string.
v
Note: To have the compiler automatically add the null character to certain
character arguments, you can use the “-qnullterm Option” on page 206.
Pascal’s character-variable data types are STRING, PACKED ARRAY OF
CHAR, GSTRING, and PACKED ARRAY OF GCHAR. The STRING data type
has a two-byte string length that is usually aligned on a half-word boundary
followed by a set of contiguous bytes, one character per byte. The dynamic
length of the string can be determined using the predefined Pascal function
LENGTH. Packed arrays of CHAR, like Fortran’s CHARACTER type, are stored
as a set of contiguous bytes, one character per byte.
If you are writing both parts of the mixed-language program, you can make the C
routines deal with the extra Fortran length argument, or you can suppress this
extra argument by passing the string using the %REF function. If you use %REF,
which you typically would for pre-existing C routines, you need to indicate where
the string ends by concatenating a null character to the end of each character string
that is passed to a C routine:
! Initialize a character string to pass to C.
character*6 message1 /’Hello\0’/
! Initialize a character string as usual, and append the null later.
character*5 message2 /’world’/
! Pass both strings to a C function that takes 2 (char *) arguments.
call cfunc(%ref(message1), %ref(message2 // ’\0’))
end
For compatibility with C language usage, you can encode the following escape
sequences in XL Fortran character strings:
Table 25. Escape Sequences for Character Strings
Escape
Meaning
\b Backspace
\f Form feed
\n New-line
\t Tab
\0 Null
\’ Apostrophe (does not terminate a string)
\" Double quotation mark (does not terminate a string)
\ \ Backslash
Interlanguage Calls 351