Ifort Bug with unary minus after operator

[Sagan__David]

Consider the following program: program bug real a,b,c a = 1.0 c = 2.0 write(*,*) "FOO: ", a/-1.0/c write(*,*) "FOO: ", a/1.0/c b = a/-1.0/c write(*,*) "FOO: ", b end program Running with ifort 17.0.7 gives: > ifort bug.f90 -O0 > ./a.out FOO: -2.000000 FOO: 0.5000000 FOO: -0.5000000 Notice that the first and third print statements should give the same results. Also note that, in any case, using a unary minus after an operator without parentheses is not a good idea and should be avoided.

[Juergen_R_R]

The code violates the Fortran standard. Two consecutive unary operators, - and / are not allowed. This is considered as extension, and the processor (compiler) can do whatever it wants. Possibly ifort decides to first execute the second fraction, giving -0.5, and then 1.0/(-0.5) gives -2.000. ifort -e08 rejects the code, nagfor rejects it always, and also gfortran with -std=f2008 rejects it. Without this, it accepts it as extension giving the desired result, but you should never count on that.

[mecej4]

Threads/articles with similar topics:

     https://software.intel.com/en-us/forums/intel-visual-fortran-compiler-for-windows/topic/799570

     https://software.intel.com/en-us/forums/intel-fortran-compiler-for-linux-and-mac-os-x/topic/759702

     https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vncp/index.html

     https://groups.google.com/forum/#!topic/comp.lang.fortran/MAOcu3EoCjs