TRANSFER Intrinsic

Most languages have a facility to change the type of an area of storage, in FORTRAN 77 people used EQUIVALENCE. Fortran 90 adds a different facility. The TRANSFER intrinsic converts (not coerces) a physical representation between data types; it is a retyping facility. The intrinsic takes the bit pattern of the underlying representation and interprets it as a different type. The intrinsic has the following syntax:

 
TRANSFER(SOURCE,MOLD)

where SOURCE is the object to be retyped and MOLD is an object of the target type. For example,

    REAL, DIMENSION(10)    :: A, AA
    INTEGER, DIMENSION(20) :: B
    COMPLEX, DIMENSION(5)  :: C
     ...
    A  = TRANSFER(B, (/ 0.0 /))
    AA = TRANSFER(B, 0.0)
    C  = TRANSFER(B, (/ (0.0,0.0) /))
     ...

The same bit pattern is used for each variable type:

 
Figure: Visualisation of the TRANSFER Intrinsic

the variable will take on the number defined by its bit pattern.

The above example highlights the following points:

• SOURCE can be array or scalar valued of any type,
• MOLD can be array or scalar valued of any type and specifies the result type (which is the same shape as SOURCE),
• in the example there is a big difference between MOLD being array valued (/ 0.0 /) and scalar 0.0
  • the result of TRANSFER(B, (/ 0.0 /)) is an array, this is assigned element-by-element to A
  • the result of TRANSFER(B, 0.0) is a scalar, this scalar is assigned to every element of AA. (The first half of B(1) (4 bytes) is interpreted as a REAL number.)
• (/ (0.0,0.0) /) represents an array valued COMPLEX variable.

Return to corresponding overview page