Logical Variable in mixed programming.

ayaz · ‎10-23-2003

I am working on a mixed programming project (C++ and Fortran). I am using MS VC++ 6.0 and CVF 6.6B. I want to share variables, which are defined in Fortran to C++ side.

Could any boday help me, how can I share Fortran's "Logical variables" at C++ side.

Jugoslav_Dujic · ‎10-23-2003

Basically, it's the same as integer/int. In C++, it can be also spelled as a BOOL or bool. What makes it LOGICAL is more context than its contents.

C/C++ treat logical expressions as false if their value is zero, and true otherwise. Fortran standard does not specify contents of a LOGICAL, only behaviour.

The only potential gotcha is CVF default convention where only least-significant byte of a LOGICAL is tested (it is a historic remnant from VAX days) -- if it's zero, it evaluates to .FALSE., otherwise .TRUE. Other bits are not tested. Thus:

logical:: b
b = 1
write(*,*) b  !Outputs "T"
b = 2
write(*,*) b  !Outputs "F"

/fpscomp:logicals compiler switch changes that behaviour, so that it's the same as C++ (0=.false., /=0 =.true.)

Jugoslav