g77.info: Functions

Functions (FUNCTION and RETURN)

   `g77' handles in a special way functions that return the following
types:

   * `CHARACTER'

   * `COMPLEX'

   * `REAL(KIND=1)'

   For `CHARACTER', `g77' implements a subroutine (a C function
returning `void') with two arguments prepended: `__g77_result', which
the caller passes as a pointer to a `char' array expected to hold the
return value, and `__g77_length', which the caller passes as an
`ftnlen' value specifying the length of the return value as declared in
the calling program.  For `CHARACTER*(*)', the called function uses
`__g77_length' to determine the size of the array that `__g77_result'
points to; otherwise, it ignores that argument.

   For `COMPLEX', when `-ff2c' is in force, `g77' implements a
subroutine with one argument prepended: `__g77_result', which the
caller passes as a pointer to a variable of the type of the function.
The called function writes the return value into this variable instead
of returning it as a function value.  When `-fno-f2c' is in force,
`g77' implements a `COMPLEX' function as `gcc''s `__complex__ float' or
`__complex__ double' function (or an emulation thereof, when
`-femulate-complex' is in effect), returning the result of the function
in the same way as `gcc' would.

   For `REAL(KIND=1)', when `-ff2c' is in force, `g77' implements a
function that actually returns `REAL(KIND=2)' (typically C's `double'
type).  When `-fno-f2c' is in force, `REAL(KIND=1)' functions return
`float'.