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13.3 Functions (FUNCTION and RETURN)

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

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.