Shape specification

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1

Are there any drawbacks of omitting shape specifications in array initiation and operation?

real :: x(5), y(5), z(5)

!without shape specification
x = 1e-1
y = 2e-1
z = x + y

!with shape specification
x(:) = 1e-1
y(:) = 2e-1
z(:) = x(:) + y(:)
3

I prefer writing x to x(:) when the whole array is being referenced. The pros and cons of the two syntaxes are discussed here. Writing just x is more concise and may sometimes lead to a faster program, but writng x(:) on the LHS prevents accidental allocation upon assignment.

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5

For the program

integer, allocatable :: vec(:)
allocate (vec(2))
vec(:) = [1,4,9]
print*,vec
vec = [1,4,9]
print*,vec
end

ifort -stand:f18 -check:bounds alas.f90 gives at run-time

forrtl: severe (408): fort: (10): Subscript #1 of the array VEC has value 3 which is greater than the upper bound of 2

so if the programmer wants to assign vec without allowing it to change size, writing vec(:) on the LHS is preferred.

Compiled with gfortran -std=f2018 -Wall -Wextra -fbounds-check -g alas.f90 the program output is

           1           4
           1           4           9

Is there a compiler option such that gfortran gives a run-time error where Intel Fortran does?

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